Review Article Emerging Photovoltaics: Organic, Copper ...

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Review Article Emerging Photovoltaics: Organic, Copper Zinc Tin Sulphide, and Perovskite-Based Solar Cells Shraavya Rao, 1 Ankita Morankar, 1 Himani Verma, 1 and Prerna Goswami 2 1 Chemical Engineering Department, Institute of Chemical Technology, Matunga, Mumbai 400019, India 2 General Engineering Department, Institute of Chemical Technology, Matunga, Mumbai 400019, India Correspondence should be addressed to Shraavya Rao; [email protected] Received 10 April 2016; Revised 27 July 2016; Accepted 9 August 2016 Academic Editor: Junsheng Yu Copyright © 2016 Shraavya Rao et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. As the photovoltaics industry continues to grow rapidly, materials other than silicon are being explored. e aim is to develop technologies that use environmentally friendly, abundant materials, low-cost manufacturing processes without compromising on efficiencies and lifetimes. is paper discusses three of the emerging technologies, organic, copper zinc tin sulphide (CZTS), and perovskite-based solar cells, their advantages, and the possible challenges in making these technologies commercially available. 1. Introduction Solar cells are traditionally classified into first-generation, second-generation, and third-generation solar cells. e first- generation cells are based mainly on silicon wafers, the commercially predominant technology. e first crystalline solar cells were fabricated at Bell Laboratory, achieving 4.5% efficiency in 1953. In 1954, an efficiency of about 6% was achieved. Over the next decade, efficiencies of around 15% were achieved. Since then, the efficiency of these cells has risen to over 20% [1]. Crystalline silicon technology accounted for about 90% of solar cell production, in 2008 [2]. Currently silicon is used extensively in solar cell devices, even though silicon has many limitations. e extensive use of silicon can be attributed to the fact that silicon technology was highly developed at the time of develop- ment of photovoltaic devices. Silicon, being widely available and relatively inexpensive, currently dominates the market. However, the manufacturing of silicon in bulk is an energy- intensive process and leads to higher costs. Also, due to the mechanical fragility of silicon, a sheet of strong glass is required to provide mechanical support, further increasing costs. However, given the abundance of silicon, its relatively high efficiencies, the well-developed material and device technology, our understanding of the physics involved, and the long term stability of silicon devices, it seems likely that crystalline silicon will dominate the market for a long time. e second-generation cells are less material-intensive and avoid use of silicon wafers. Due to lower material con- sumption, they have lower manufacturing costs. ey have lower efficiencies than first-generation cells. ey include devices based on amorphous silicon, CdTe, and Cu(In,Ga)Se 2 (CIGS). However, these cells have several shortcomings. Typically, their efficiencies are much lower than conventional silicon-based cells. CdTe panels in commercial use currently achieve about 10%. Other shortcomings include the use of relatively rarer elements, such as Te in CdTe solar cells. In comparison, CIGS cells have efficiencies similar to that of silicon cells [3]. CIGS and CdTe are the only thin film technologies that have seen commercial success. As the global photovoltaic (PV) market continues to grow, the focus is on developing technologies that use environmentally friendly, abundant materials, low-cost manufacturing processes with- out compromising on efficiencies and lifetimes. ese “third- generation” technologies still require further study and research before they can be made available commercially. ese technologies include organic solar cells, perovskite solar cells, and copper zinc tin sulphide (CZTS) solar cells. In particular, perovskite solar cells have attracted a lot of attention as their efficiencies have gone over 20% [4]. In this paper, we have presented a basic overview of some of the most promising new developments in this field. e paper will concentrate on organic, CZTS, and perovskite materials. e paper discusses these materials, the possibility Hindawi Publishing Corporation Journal of Applied Chemistry Volume 2016, Article ID 3971579, 12 pages http://dx.doi.org/10.1155/2016/3971579

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Review ArticleEmerging Photovoltaics Organic Copper Zinc Tin Sulphideand Perovskite-Based Solar Cells

Shraavya Rao1 Ankita Morankar1 Himani Verma1 and Prerna Goswami2

1Chemical Engineering Department Institute of Chemical Technology Matunga Mumbai 400019 India2General Engineering Department Institute of Chemical Technology Matunga Mumbai 400019 India

Correspondence should be addressed to Shraavya Rao shraavyargmailcom

Received 10 April 2016 Revised 27 July 2016 Accepted 9 August 2016

Academic Editor Junsheng Yu

Copyright copy 2016 Shraavya Rao et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

As the photovoltaics industry continues to grow rapidly materials other than silicon are being explored The aim is to developtechnologies that use environmentally friendly abundant materials low-cost manufacturing processes without compromising onefficiencies and lifetimes This paper discusses three of the emerging technologies organic copper zinc tin sulphide (CZTS) andperovskite-based solar cells their advantages and the possible challenges in making these technologies commercially available

1 Introduction

Solar cells are traditionally classified into first-generationsecond-generation and third-generation solar cellsThe first-generation cells are based mainly on silicon wafers thecommercially predominant technology The first crystallinesolar cells were fabricated at Bell Laboratory achieving45 efficiency in 1953 In 1954 an efficiency of about 6was achieved Over the next decade efficiencies of around15 were achieved Since then the efficiency of these cellshas risen to over 20 [1] Crystalline silicon technologyaccounted for about 90 of solar cell production in 2008[2] Currently silicon is used extensively in solar cell deviceseven though silicon has many limitations The extensiveuse of silicon can be attributed to the fact that silicontechnology was highly developed at the time of develop-ment of photovoltaic devices Silicon being widely availableand relatively inexpensive currently dominates the marketHowever the manufacturing of silicon in bulk is an energy-intensive process and leads to higher costs Also due tothe mechanical fragility of silicon a sheet of strong glass isrequired to provide mechanical support further increasingcosts However given the abundance of silicon its relativelyhigh efficiencies the well-developed material and devicetechnology our understanding of the physics involved andthe long term stability of silicon devices it seems likely thatcrystalline silicon will dominate the market for a long time

The second-generation cells are less material-intensiveand avoid use of silicon wafers Due to lower material con-sumption they have lower manufacturing costs They havelower efficiencies than first-generation cells They includedevices based on amorphous silicon CdTe andCu(InGa)Se

2

(CIGS) However these cells have several shortcomingsTypically their efficiencies are much lower than conventionalsilicon-based cells CdTe panels in commercial use currentlyachieve about 10 Other shortcomings include the use ofrelatively rarer elements such as Te in CdTe solar cellsIn comparison CIGS cells have efficiencies similar to thatof silicon cells [3] CIGS and CdTe are the only thin filmtechnologies that have seen commercial success As the globalphotovoltaic (PV) market continues to grow the focus is ondeveloping technologies that use environmentally friendlyabundant materials low-cost manufacturing processes with-out compromising on efficiencies and lifetimesThese ldquothird-generationrdquo technologies still require further study andresearch before they can be made available commerciallyThese technologies include organic solar cells perovskitesolar cells and copper zinc tin sulphide (CZTS) solar cellsIn particular perovskite solar cells have attracted a lot ofattention as their efficiencies have gone over 20 [4]

In this paper we have presented a basic overview of someof the most promising new developments in this field Thepaper will concentrate on organic CZTS and perovskitematerials The paper discusses these materials the possibility

Hindawi Publishing CorporationJournal of Applied ChemistryVolume 2016 Article ID 3971579 12 pageshttpdxdoiorg10115520163971579

2 Journal of Applied Chemistry

+

minus

Externalload

Electron-hole pair

Antireflection coating

Front contactEmitter

Base

Rear contact

Sunlight

Figure 1 Cross section of a typical crystalline silicon solar cell [5]

of low-cost processing and their performances It examinesthe commercial viability of these technologies We have alsodiscussed the probability of the large-scale manufacture ofthese devices and the various processing techniques

2 General Structure of Solar Cell Devices

The photovoltaic effect is a process in which an electricvoltage is developed at the junction between two dissimilarmaterials upon illumination The most common applicationof the photovoltaic effect is in solar cells where sunlight isconverted into electricity Practically almost all solar cellsconsist of semiconductor materials and incorporate a p-njunction A cross section of a typical crystalline silicon solarcell is shown in Figure 1

The material used in the solar cell must have the capacityto absorb a large portion of the solar radiation spectrumBased on the absorption coefficient of the material light isabsorbed close to the surface of the cell The absorption ofphotons from sunlight leads to the generation of electron-hole pairs If these electron-hole pairs reach the p-n junctionthe carriers are separated due to the electric field present atthe junction In most solar cells the generation of chargecarriers occurs close to the surface

The material used in the solar cell must preferablybe highly crystalline Also a semiconductor can give goodefficiency of photon absorption only if the energy of thephoton is close to the band gap The material must also havehigh absorption coefficient indicating good absorption oflight This is the general structure in silicon-based devicesHowever as interest in photovoltaics research continues togrow modifications have been made for better performanceThe general device structure for each material will be dis-cussed separately

3 Organic Solar Cell

The photovoltaic effect in organic materials had beendescribed as far back as the late 1950s by Melvin CalvinPhotoconductivity in organic molecules was first observed inanthracene 1906 In the late 1950s and 1960s when crystallinesolar cells were proved to be commercially viable scientificinterest in photoconductivity and related subjects spikedand the potential of organic molecules was studied In theearly 1960s the semiconducting properties of many organicdyes were discovered and the photovoltaic effect was later

observed in these dyes Also many biological molecules suchas carotenes and porphyrins exhibited the same effect Inspite of this organic photovoltaic devices never reached thecommercial popularity of crystalline solar cells [11] Muchwork was carried out in this field during the 1970s 1980sdecades The oldest simplest form of organic solar cells wasbased on a single active layer structure with an organicfilm sandwiched between two metal electrodes of differingwork functions Generally the power conversion efficiencieswere usually less than 001 [12] In 1986 Tang introducedthe concept of a bilayer architecture in which two organicmaterials one acting as an electron donor and the other as anelectron acceptor were sandwiched between the electrodesThe resulting device exhibited improved efficiencies of about1 [12] For many years following this development efficien-cies remained limited to about 1 The last two decades haveseen a large amount of work dedicated to an improved under-standing of the transport mechanisms in organic devicesThe introduction of conjugated polymers led to increasedinterest in organic photovoltaic devices and photovoltaiccells were based on these new materials The concept ofa tandem cell structure was introduced later Lately theemphasis has shifted to using simple novel techniques foroptimization and improving power conversion efficienciesThese techniques include proper choice of solvents andthermal treatment of solution processed polymer cells [13]Efficiencies have gone up to around 10 in recent yearswhich is the threshold efficiency for commercial applications[9] Efficiencies of around 8 have been achieved by solutionprocessed polythiophene-fullerene cells by the use of noveloptimization techniques [12] Efficiencies of 92 have beenachieved by polymer-based devices as shown by He et al[14]

Organic semiconductors have the ability to absorb lightfrom the solar spectrum and give rise to current due to thepresence of a large conjugated system pz orbitals electronsundergo delocalization and form 120587 bonds with neighbouringpz electrons leading to a conjugated system with alter-nated single and double bonds Organic semiconductorsusually have poor charge carrier mobility generally ordersof magnitude lower than their inorganic counterparts Thishas to be taken into consideration while designing organicphotovoltaic (OPV) devices Another factor to be consid-ered is that unlike crystalline inorganic semiconductors theexciton (electron-hole pairs bound together by electrostaticinteractions) diffusion length in organicmaterials is relativelyshorter due to their more amorphous and disordered struc-ture However the relatively higher absorption coefficients(gt105 cmminus1) partiallymake up for the poormobilities and givegood absorption even with thicknesses of around 100 nmDue to the above features OPV devices generally have layerthicknesses of around 100 nm [12]

31Mechanism Themechanism of organic solar cell involvesthe generation of electron-hole pairs as opposed to freecharges Let us consider a bilayer solar cell in which twoactive organic materials namely a donor and an acceptor areplaced between two electrodes At least one electrodemust betransparent to allow light to enter [12]

Journal of Applied Chemistry 3

Electrode 1

Electrode 2

Organic electronic material

(a)

Electrode 1

Electrode 2

Electron donor

Electron acceptor

(b)

Electrode 1

Electrode 2

Dispersed heterojunction

(c)

Figure 2 Schematics of different OPV cell structures (a) single layer device (b) bilayer device and (c) bulk heterojunction device

The process involves the following

(i) Generation of excitons(ii) Exciton diffusion(iii) Exciton dissociation(iv) Charge transport

The first step involves the absorption of photons fromlight and generation of electron-hole pair (exciton) Organicsemiconductors have high absorption coefficients Thereforea layer of thickness in the range of a few hundred nanometresis sufficient to absorb the incident light The absorbed lighttriggers the generation of electron-hole pairsThis is followedby exciton diffusion The excitons thus generated generallyhave lifetimes in the range of few picoseconds which limitstheir mobility The mobility of excitons is limited to a rangeof 10 nmThis is called exciton diffusion length and is crucialin the design and performance of organic solar cells Theexciton thus generated undergoes dissociation The electro-statically coupled electron-hole pair splits into free charges atthe donor-acceptor interface Ideally all the photogeneratedexcitons should reach a dissociation length However thisdoes not occur due to small exciton diffusion length limitingthe efficiency of the cell In the charge transport step the freecharges thus produced travel to the electrodes through thedonoracceptor materials fromwhere they enter the externalcircuit [12 36]

32 Device Structures The common basic OPV cell struc-tures include the following

321 Single Active Layer Cells Figure 2(a) illustrates thedevice structure of a single active layer cell Here a thinfilm of organic semiconductor is sandwiched between twoelectrodes A layer of high work function (eg IndiumTitaniumOxide (ITO)) and a layer having low work function(Mg Ag etc) are used as electrodes In practice these cellshave very low efficiencies (quantum efficiencies lt 1 andpower conversion efficiencies lt 01) and do not work verywell [12 36]

322 Bilayer Cells Two organic materials one acting as adonor and the second as an acceptor are sandwiched betweentwo electrodes (as shown in Figure 2(b)) Higher efficiency

of exciton dissociation makes these devices more efficientthan single layer devices These devices have achieved powerconversion efficiencies of around 36 using copper phthalo-cyanine and C

60[12 36]

323 Bulk Heterojunction Donor and acceptor materialsare mixed to form a bulk heterojunction Figure 2(c) showsstructure of the bulk heterojunction Bulk heterojunctionmaterials have many favourable properties including highphotosensitivity and energy conversion efficiency The pres-ence of illumination induces transfer of electrons fromdonor-type semiconducting conjugated polymer to acceptor-type conjugated polymers or molecules like Buckminster-fullerene C

60 Power conversion efficiencies of above 35

have been achieved using solution-cast P3HTPCBM blends[12 36]

324 Diffuse Bilayer Heterojunction This device structureaims to adapt the advantages of both the bilayer and bulkheterojunction devices It provides a larger donor-acceptorinterface area and a spatially uninterrupted pathway forcharge carriers [12]

33 Preparation of Organic Solar Cell Materials Two of thecommonly used techniques for materials synthesis are evap-oration and solution processing The choice of techniquesdepends upon the material to be used Thermal stability ofthe material has to be considered while using evaporationtechniques Similarly solubility of material is required forsolution processing The processing has significantly lowercosts as compared to inorganic materials and offers a greatdeal of versatility [12 36]

Polymer solar cells are usually fabricated by solutionprocessing at low temperatures as polymer molecules maydegrade at high temperatures Conjugated semiconductingpolymers are fabricated by printing and coating techniquessuch as spin-coating screen printing and doctor blading Ingeneral solution processes are preferred to vacuumprocessesdue to its lower energy requirements and cost effectiveness[12]

34 Potential Materials for Organic Solar Cells In organicsolar cells a layer of organic material acting as activelayer is sandwiched between two electrodes The organic

4 Journal of Applied Chemistry

N HN

N

N

NH

N

N

N

(a) Phthalocyanine

NH N

N HN

(b) Porphyrin (c) Fullerene [6]

S

S

S

S

S

S

(d) Polythiophene [7]

NH

O

O(e) Phthalimide [8]

Figure 3 Organic molecules used as electron donors and electron acceptors in organic solar cells

semiconductor must be either an electron donor or anelectron acceptor material The active layer consists of bothelectron donor and electron acceptor material [12]

341ElectronDonorMaterials Phthalocyanines (Figure 3(a))and their homologues have been commonly used as elec-tron donor materials Phthalocyanines (Pc) as shown inFigure 3(a) are 2D 18 pi electron aromatic porphyrin syntheticanalogues in which four isoindole units are joined by Natoms Also copper phthalocyanine and zinc phthalocyaninehave been used as donor materials Double heterojunc-tion CuPcC

60thin film cells with Ag cathode have given

efficiencies of about 4 [37 38] Further work on thesame CuPcC

60cell with hybrid planar-mixed molecular

heterojunctions has given efficiencies of around 55 [1214 36ndash40] Subphthalocyanines the lowest homologues ofphthalocyanines have shown promise due to their chemistryand properties CuPcC

60based cells have given greater

119881oc as compared to CuPcC60

based cells thus increasingefficiency [41] Porphyrins (Figure 3(b)) and their derivativeshave also been used as electron donors [12 14 36ndash40]These oligomer organic materials are however not alwayscompatible with the flexible electronics Most of them cannotbe obtained through solution processing and require thermal

evaporation techniques leading to increase in cost [12 14 36ndash38] Polymer-based organic solar cells can be obtained viasolution processing thus making them compatible with theflexible substrate and also reducing costs [42]

Polythiophene (Figure 3(d)) derivatives and fullerene(Figure 3(c)) derivatives have been blended together toformbulk heterojunction structures Poly(3-alkylthiophene)s(P3AT) in particular have shown great promise as elec-tron donor materials P3HT has given the best resultsP3HTPCBM ([66]-phenyl C

61-butyric acid methyl ester)

based devices have given efficiencies of around 5 [4042 43] Benzodithiophene derivatives have shown greatpromise for use in PSC and related areas Benzo(12-b 45-b1015840)dithiophene (BDT) has great potential for use in PSCs119881oc (open circuit voltage) and Jsc (short circuit current) ofBDT derivatives were 075 V and 38mAcm2 respectivelycorresponding to a PCE of 16 which indicates that BDT is apromising commonunit of photovoltaic conjugated polymers[43]

Recently phthalimide (Figure 3(e)) has emerged as anattractive candidate for electron-accepting unit in the donor-acceptor (D-A) copolymers due to its extremely facile syn-thesis and readily varied substitution at the imide nitro-gen allowing manipulation of polymer solubility packing

Journal of Applied Chemistry 5

Table 1 Power conversion efficiencies of some organic solar cells

Device configuration 119869sc (short circuitcurrent) in mA cmminus2

119881oc (open circuitvoltage) in V Fill factor PCE () Ref

ITOPFNPTB7PC71BMMoO

3Al 175 075 070 92 [14]

ITOZnO-PVPPDTS-TPDPC71BMMoO

3Ag 144 086 069 85 [15]

ITOTiPDPBDTTTCPC71BMMoO

3Ag 163 070 065 74 [16]

ITOPEDOTPSSPBnDTDTffBTPC61BMCaAl 129 091 061 72 [17]

ITOPEDOTPSSPIDT-phanQPC71BMC

60-bisAg 115 088 061 62 [18]

and morphology Two new D-A copolymers PDTSPhand PDTSBTPh based on dithienosilole donor unit andphthalimide acceptor unit were synthesized The powerconversion efficiency of the polymer solar cells based onPDTSBTPhPC

70BM (1 2 ww) reached 21 [44]

342 Electron Acceptor Materials Fullerenes (Figure 3(c))and their derivatives are the most commonly used acceptormaterials Fullerene can be reversibly reduced with up to6 electrons which has led to it being commonly used asan electron acceptor C

60has limited solubility in most

organic solvents To increase the solubility and to avoidsevere phase separation of DA blend [66]-phenyl C

60

butyric acid methyl ester (PC60BM) has been used as itcan be solution processed The PC70BM derivative has alsobeen studied but though it has stronger absorption in thevisible range it is more expensive than C

60due to the

purification processes [12 14 36ndash39] Indene-fullerenes havealso been used as electron acceptor materials specificallyindene-fullerene bisadduct (ICBA) and indene-fullerenemonoadduct (ICMA) These can be synthesized easily via aone-pot reaction ICBAP3HT and ICMAP3HT have givenhigher 119881oc than P3HTPCBM devices [12 14] Lately C

60

derivatives with oligo(phenyleneethynediyl) (OPE) subunitshave been studied [45]

SubPc has also been used an acceptor material Tetraceneas a donor and SubPc as an acceptor have been used and effi-ciencies have reached 29 Fluorinated subphthalocyanine(F16SubPc) also shows potential as electron donor [12]Table 1 gives a few materials and their efficiencies along

with the device type in an organic solar cell The highestefficiency for organic solar cells is around 11 (Toshiba) [31]

4 CZTS Solar Cells

The thin film solar cell technology is growing in both capacityand market share Currently it accounts for around 20 ofthe PV market [46] CdTe solar cells account for about 10and the remainder is divided between thin film silicon andCu(InGa)Se

2(CIGS) where CIGS is growing rapidly The

main advantage for CIGS solar cells is the high efficiencywhich has currently crossed 20 Currently the best thin filmsolar cells have above 20 efficiency and are based on CIGS[46ndash49]

Recently quaternary compound Cu2ZnSn(SSe)

4has

been studied as a potential photovoltaic material due to itssimilarities with CIGS (Cu(InGa)Se

2) in material proper-

ties and the relative availability of raw materials CZTS is

Sunlight

TCOi-ZnOn-CdS

CZTS light absorberMo-coated substrate

Glass

Figure 4 Structure of CZTS solar cell [9]

a compound semiconductor in the form (I)2(II)(IV)(VI)

4 It

possesses a relatively high absorption coefficient (gt104 cmminus1)and a band gap of around 145 eV [47]Theoretically efficien-cies of around 32 have been calculated for CZTS thin filmsolar cells having a layer of CZTS several micrometers thick[46ndash49]

41 Basic Structure Schematic diagram of CZTS solar cellstructure is shown in Figure 4 Molybdenum thin film havingthickness of 500ndash700 nm is deposited on glass substrate andacts as a back contact Molybdenum has high stability inharsh reactive conditions such as sulphur-containing vaporand high temperaturesThe absorber layer p-type CZTS thinfilm is deposited on Mo layer having thickness in the rangeof 1-2 micrometers To form a p-n junction CdS layer havingthickness of 50ndash100 nm is coated on CZTS layer The CZTSsurface is uneven and cannot be completely covered by CdSthin filmThismay cause shorting between the front and backcontacts To avoid leakage 50ndash90 nm intrinsic ZnO thin filmis coated on CdS layer Then transparent conducting oxidethin film is deposited and acts as the front contact [47 48]

42 Fabrication of CZTS Devices421 Vacuum Techniques All the elements are simultane-ously incorporated in a single step in one-step vacuum pro-cessesThese techniques include cosputtering and coevapora-tion both of which give devices with good performance [48]Pulsed-laser deposition is a two-step process wherein the firststep incorporates the precursors in an ambient-temperatureprocess like sputtering or evaporation This is followed byannealing The incorporation of chalcogens can occur ineither step [47 48]

6 Journal of Applied Chemistry

Table 2 Comparison of CZTS cells fabricated by different processes

Method Precursor Efficiency () Comments

Vacuum thermalevaporation Cu Zn Sn S 84 [19]

Has been used commercially fast process compared tosputtering better purity high energy requirements tocreate vacuum difficulties in scaling up thicknesscontrol may be problematic

Sputtering Cu SnS ZnS 677 [20]Slower than evaporation scaling up is easier highercapital costs accounts for significant part ofcommercial production of CIGS cells vacuum processleading to higher energy requirements cost-effective

Electrodeposition Cu(II) ion Zn(II) ionSn(IV) ion 73 [21]

Generally more environmentally friendly usuallynontoxic for copper zinc tin electrodeposition iscarried out at room temperature reducing energyrequirements has been commercially used thicknesscontrol may be problematic

Sol-gel based method

Copper (II) acetatemonohydrate

Zinc (II) acetate dehydrateTin (II) chloride dehydrate

223 [22] Simple and versatile cost-effective environmentallyfriendly due to lower temperatures

Pulsed laser deposition In-house fabricated CZTSpellet 314 [23]

Vacuum process higher energy requirements scalingup difficulties composition and thickness dependenceon deposition conditions not yet well understood

422 Nonvacuum Techniques These processes include elec-trodeposition sol-gel based methods and spray coatingThey are scalable and cheaper which makes them suitablefor large-scale processes The highest efficiency of CZTSSecell (126) has been achieved by nonvacuum techniquessimultaneous use of spin-coating solution and particles ofconstituents Other promising methods are nanoparticlesand electroplating [47 48] Electrochemical deposition alsoappears to be a promising preparation method [47] Table 2shows a comparison of some of the processing techniques

5 Perovskites

Perovskites are materials described by the formula ABX3

where A B are cations A is bigger than B and X is an anionTheir structure is similar to the structure of calcium titanateFigure 5 shows the crystal structure of a typical perovskitestructured compound CH

3NH3Pb [10]

51 Hybrid Halide Perovskites In solar cells organic-inorganic halide perovskites are most commonly usedwhere A is an organic cation and X is a halide usually Iodinethough Cl and Br have also been used A is usually themethylammonium cation (CH

3NH3

+) However ethyl ammonium(CH3CH2NH3

+) and formamidinium (NH2CH=NH

2

+)are also used as cations Cl and Br are typically used in amixed halide material B is usually Pb or Sn due to bandgap considerations However due to the lower stability ofSn and the relative ease with which it is oxidized to SnI

4 Pb

is generally preferred Structure of methyl ammonium leadis shown in Figure 5 Lead has weak tendency to undergooxidization due to relativistic effects Therefore methylammonium lead triiodide is generally taken as the standardcompound though mixed halides CH

3NH3PbI3minusxClx and

CH3NH3PbI3minusxClx are also considered important Forma-

Figure 5 Structure of CH3NH3Pb [10]

midinium lead trihalide (H2NCHNH

2PbX3) has also shown

potential with band gaps in the range of 15 to 22 eV [50 51]The perovskite properties have been known for many

years However perovskite materials were first utilized ina photovoltaic device in 2009 This device was based ona dye-sensitized solar cell architecture using perovskiteas a sensitizer and achieved an efficiency of 38 forCH3NH3PbI3cells The main drawback was the cell stability

as the lifetime was in minutes In 2012 Snaith and hiscoworkers achieved a breakthrough with efficiencies goingabove 10 and demonstrated that perovskites played a role inthe transport of electrons and holes towards the cell terminallaying the basis for planar cells [52] Thus far research inperovskite cells has mainly concentrated on CH

3NH3PbI3

and CH3NH3PbI3minusxClx Currently high efficiencies over 20

have been achieved by perovskite devices [30] based on

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

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Journal of

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Analytical ChemistryInternational Journal of

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Journal of

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Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

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CatalystsJournal of

Page 2: Review Article Emerging Photovoltaics: Organic, Copper ...

2 Journal of Applied Chemistry

+

minus

Externalload

Electron-hole pair

Antireflection coating

Front contactEmitter

Base

Rear contact

Sunlight

Figure 1 Cross section of a typical crystalline silicon solar cell [5]

of low-cost processing and their performances It examinesthe commercial viability of these technologies We have alsodiscussed the probability of the large-scale manufacture ofthese devices and the various processing techniques

2 General Structure of Solar Cell Devices

The photovoltaic effect is a process in which an electricvoltage is developed at the junction between two dissimilarmaterials upon illumination The most common applicationof the photovoltaic effect is in solar cells where sunlight isconverted into electricity Practically almost all solar cellsconsist of semiconductor materials and incorporate a p-njunction A cross section of a typical crystalline silicon solarcell is shown in Figure 1

The material used in the solar cell must have the capacityto absorb a large portion of the solar radiation spectrumBased on the absorption coefficient of the material light isabsorbed close to the surface of the cell The absorption ofphotons from sunlight leads to the generation of electron-hole pairs If these electron-hole pairs reach the p-n junctionthe carriers are separated due to the electric field present atthe junction In most solar cells the generation of chargecarriers occurs close to the surface

The material used in the solar cell must preferablybe highly crystalline Also a semiconductor can give goodefficiency of photon absorption only if the energy of thephoton is close to the band gap The material must also havehigh absorption coefficient indicating good absorption oflight This is the general structure in silicon-based devicesHowever as interest in photovoltaics research continues togrow modifications have been made for better performanceThe general device structure for each material will be dis-cussed separately

3 Organic Solar Cell

The photovoltaic effect in organic materials had beendescribed as far back as the late 1950s by Melvin CalvinPhotoconductivity in organic molecules was first observed inanthracene 1906 In the late 1950s and 1960s when crystallinesolar cells were proved to be commercially viable scientificinterest in photoconductivity and related subjects spikedand the potential of organic molecules was studied In theearly 1960s the semiconducting properties of many organicdyes were discovered and the photovoltaic effect was later

observed in these dyes Also many biological molecules suchas carotenes and porphyrins exhibited the same effect Inspite of this organic photovoltaic devices never reached thecommercial popularity of crystalline solar cells [11] Muchwork was carried out in this field during the 1970s 1980sdecades The oldest simplest form of organic solar cells wasbased on a single active layer structure with an organicfilm sandwiched between two metal electrodes of differingwork functions Generally the power conversion efficiencieswere usually less than 001 [12] In 1986 Tang introducedthe concept of a bilayer architecture in which two organicmaterials one acting as an electron donor and the other as anelectron acceptor were sandwiched between the electrodesThe resulting device exhibited improved efficiencies of about1 [12] For many years following this development efficien-cies remained limited to about 1 The last two decades haveseen a large amount of work dedicated to an improved under-standing of the transport mechanisms in organic devicesThe introduction of conjugated polymers led to increasedinterest in organic photovoltaic devices and photovoltaiccells were based on these new materials The concept ofa tandem cell structure was introduced later Lately theemphasis has shifted to using simple novel techniques foroptimization and improving power conversion efficienciesThese techniques include proper choice of solvents andthermal treatment of solution processed polymer cells [13]Efficiencies have gone up to around 10 in recent yearswhich is the threshold efficiency for commercial applications[9] Efficiencies of around 8 have been achieved by solutionprocessed polythiophene-fullerene cells by the use of noveloptimization techniques [12] Efficiencies of 92 have beenachieved by polymer-based devices as shown by He et al[14]

Organic semiconductors have the ability to absorb lightfrom the solar spectrum and give rise to current due to thepresence of a large conjugated system pz orbitals electronsundergo delocalization and form 120587 bonds with neighbouringpz electrons leading to a conjugated system with alter-nated single and double bonds Organic semiconductorsusually have poor charge carrier mobility generally ordersof magnitude lower than their inorganic counterparts Thishas to be taken into consideration while designing organicphotovoltaic (OPV) devices Another factor to be consid-ered is that unlike crystalline inorganic semiconductors theexciton (electron-hole pairs bound together by electrostaticinteractions) diffusion length in organicmaterials is relativelyshorter due to their more amorphous and disordered struc-ture However the relatively higher absorption coefficients(gt105 cmminus1) partiallymake up for the poormobilities and givegood absorption even with thicknesses of around 100 nmDue to the above features OPV devices generally have layerthicknesses of around 100 nm [12]

31Mechanism Themechanism of organic solar cell involvesthe generation of electron-hole pairs as opposed to freecharges Let us consider a bilayer solar cell in which twoactive organic materials namely a donor and an acceptor areplaced between two electrodes At least one electrodemust betransparent to allow light to enter [12]

Journal of Applied Chemistry 3

Electrode 1

Electrode 2

Organic electronic material

(a)

Electrode 1

Electrode 2

Electron donor

Electron acceptor

(b)

Electrode 1

Electrode 2

Dispersed heterojunction

(c)

Figure 2 Schematics of different OPV cell structures (a) single layer device (b) bilayer device and (c) bulk heterojunction device

The process involves the following

(i) Generation of excitons(ii) Exciton diffusion(iii) Exciton dissociation(iv) Charge transport

The first step involves the absorption of photons fromlight and generation of electron-hole pair (exciton) Organicsemiconductors have high absorption coefficients Thereforea layer of thickness in the range of a few hundred nanometresis sufficient to absorb the incident light The absorbed lighttriggers the generation of electron-hole pairsThis is followedby exciton diffusion The excitons thus generated generallyhave lifetimes in the range of few picoseconds which limitstheir mobility The mobility of excitons is limited to a rangeof 10 nmThis is called exciton diffusion length and is crucialin the design and performance of organic solar cells Theexciton thus generated undergoes dissociation The electro-statically coupled electron-hole pair splits into free charges atthe donor-acceptor interface Ideally all the photogeneratedexcitons should reach a dissociation length However thisdoes not occur due to small exciton diffusion length limitingthe efficiency of the cell In the charge transport step the freecharges thus produced travel to the electrodes through thedonoracceptor materials fromwhere they enter the externalcircuit [12 36]

32 Device Structures The common basic OPV cell struc-tures include the following

321 Single Active Layer Cells Figure 2(a) illustrates thedevice structure of a single active layer cell Here a thinfilm of organic semiconductor is sandwiched between twoelectrodes A layer of high work function (eg IndiumTitaniumOxide (ITO)) and a layer having low work function(Mg Ag etc) are used as electrodes In practice these cellshave very low efficiencies (quantum efficiencies lt 1 andpower conversion efficiencies lt 01) and do not work verywell [12 36]

322 Bilayer Cells Two organic materials one acting as adonor and the second as an acceptor are sandwiched betweentwo electrodes (as shown in Figure 2(b)) Higher efficiency

of exciton dissociation makes these devices more efficientthan single layer devices These devices have achieved powerconversion efficiencies of around 36 using copper phthalo-cyanine and C

60[12 36]

323 Bulk Heterojunction Donor and acceptor materialsare mixed to form a bulk heterojunction Figure 2(c) showsstructure of the bulk heterojunction Bulk heterojunctionmaterials have many favourable properties including highphotosensitivity and energy conversion efficiency The pres-ence of illumination induces transfer of electrons fromdonor-type semiconducting conjugated polymer to acceptor-type conjugated polymers or molecules like Buckminster-fullerene C

60 Power conversion efficiencies of above 35

have been achieved using solution-cast P3HTPCBM blends[12 36]

324 Diffuse Bilayer Heterojunction This device structureaims to adapt the advantages of both the bilayer and bulkheterojunction devices It provides a larger donor-acceptorinterface area and a spatially uninterrupted pathway forcharge carriers [12]

33 Preparation of Organic Solar Cell Materials Two of thecommonly used techniques for materials synthesis are evap-oration and solution processing The choice of techniquesdepends upon the material to be used Thermal stability ofthe material has to be considered while using evaporationtechniques Similarly solubility of material is required forsolution processing The processing has significantly lowercosts as compared to inorganic materials and offers a greatdeal of versatility [12 36]

Polymer solar cells are usually fabricated by solutionprocessing at low temperatures as polymer molecules maydegrade at high temperatures Conjugated semiconductingpolymers are fabricated by printing and coating techniquessuch as spin-coating screen printing and doctor blading Ingeneral solution processes are preferred to vacuumprocessesdue to its lower energy requirements and cost effectiveness[12]

34 Potential Materials for Organic Solar Cells In organicsolar cells a layer of organic material acting as activelayer is sandwiched between two electrodes The organic

4 Journal of Applied Chemistry

N HN

N

N

NH

N

N

N

(a) Phthalocyanine

NH N

N HN

(b) Porphyrin (c) Fullerene [6]

S

S

S

S

S

S

(d) Polythiophene [7]

NH

O

O(e) Phthalimide [8]

Figure 3 Organic molecules used as electron donors and electron acceptors in organic solar cells

semiconductor must be either an electron donor or anelectron acceptor material The active layer consists of bothelectron donor and electron acceptor material [12]

341ElectronDonorMaterials Phthalocyanines (Figure 3(a))and their homologues have been commonly used as elec-tron donor materials Phthalocyanines (Pc) as shown inFigure 3(a) are 2D 18 pi electron aromatic porphyrin syntheticanalogues in which four isoindole units are joined by Natoms Also copper phthalocyanine and zinc phthalocyaninehave been used as donor materials Double heterojunc-tion CuPcC

60thin film cells with Ag cathode have given

efficiencies of about 4 [37 38] Further work on thesame CuPcC

60cell with hybrid planar-mixed molecular

heterojunctions has given efficiencies of around 55 [1214 36ndash40] Subphthalocyanines the lowest homologues ofphthalocyanines have shown promise due to their chemistryand properties CuPcC

60based cells have given greater

119881oc as compared to CuPcC60

based cells thus increasingefficiency [41] Porphyrins (Figure 3(b)) and their derivativeshave also been used as electron donors [12 14 36ndash40]These oligomer organic materials are however not alwayscompatible with the flexible electronics Most of them cannotbe obtained through solution processing and require thermal

evaporation techniques leading to increase in cost [12 14 36ndash38] Polymer-based organic solar cells can be obtained viasolution processing thus making them compatible with theflexible substrate and also reducing costs [42]

Polythiophene (Figure 3(d)) derivatives and fullerene(Figure 3(c)) derivatives have been blended together toformbulk heterojunction structures Poly(3-alkylthiophene)s(P3AT) in particular have shown great promise as elec-tron donor materials P3HT has given the best resultsP3HTPCBM ([66]-phenyl C

61-butyric acid methyl ester)

based devices have given efficiencies of around 5 [4042 43] Benzodithiophene derivatives have shown greatpromise for use in PSC and related areas Benzo(12-b 45-b1015840)dithiophene (BDT) has great potential for use in PSCs119881oc (open circuit voltage) and Jsc (short circuit current) ofBDT derivatives were 075 V and 38mAcm2 respectivelycorresponding to a PCE of 16 which indicates that BDT is apromising commonunit of photovoltaic conjugated polymers[43]

Recently phthalimide (Figure 3(e)) has emerged as anattractive candidate for electron-accepting unit in the donor-acceptor (D-A) copolymers due to its extremely facile syn-thesis and readily varied substitution at the imide nitro-gen allowing manipulation of polymer solubility packing

Journal of Applied Chemistry 5

Table 1 Power conversion efficiencies of some organic solar cells

Device configuration 119869sc (short circuitcurrent) in mA cmminus2

119881oc (open circuitvoltage) in V Fill factor PCE () Ref

ITOPFNPTB7PC71BMMoO

3Al 175 075 070 92 [14]

ITOZnO-PVPPDTS-TPDPC71BMMoO

3Ag 144 086 069 85 [15]

ITOTiPDPBDTTTCPC71BMMoO

3Ag 163 070 065 74 [16]

ITOPEDOTPSSPBnDTDTffBTPC61BMCaAl 129 091 061 72 [17]

ITOPEDOTPSSPIDT-phanQPC71BMC

60-bisAg 115 088 061 62 [18]

and morphology Two new D-A copolymers PDTSPhand PDTSBTPh based on dithienosilole donor unit andphthalimide acceptor unit were synthesized The powerconversion efficiency of the polymer solar cells based onPDTSBTPhPC

70BM (1 2 ww) reached 21 [44]

342 Electron Acceptor Materials Fullerenes (Figure 3(c))and their derivatives are the most commonly used acceptormaterials Fullerene can be reversibly reduced with up to6 electrons which has led to it being commonly used asan electron acceptor C

60has limited solubility in most

organic solvents To increase the solubility and to avoidsevere phase separation of DA blend [66]-phenyl C

60

butyric acid methyl ester (PC60BM) has been used as itcan be solution processed The PC70BM derivative has alsobeen studied but though it has stronger absorption in thevisible range it is more expensive than C

60due to the

purification processes [12 14 36ndash39] Indene-fullerenes havealso been used as electron acceptor materials specificallyindene-fullerene bisadduct (ICBA) and indene-fullerenemonoadduct (ICMA) These can be synthesized easily via aone-pot reaction ICBAP3HT and ICMAP3HT have givenhigher 119881oc than P3HTPCBM devices [12 14] Lately C

60

derivatives with oligo(phenyleneethynediyl) (OPE) subunitshave been studied [45]

SubPc has also been used an acceptor material Tetraceneas a donor and SubPc as an acceptor have been used and effi-ciencies have reached 29 Fluorinated subphthalocyanine(F16SubPc) also shows potential as electron donor [12]Table 1 gives a few materials and their efficiencies along

with the device type in an organic solar cell The highestefficiency for organic solar cells is around 11 (Toshiba) [31]

4 CZTS Solar Cells

The thin film solar cell technology is growing in both capacityand market share Currently it accounts for around 20 ofthe PV market [46] CdTe solar cells account for about 10and the remainder is divided between thin film silicon andCu(InGa)Se

2(CIGS) where CIGS is growing rapidly The

main advantage for CIGS solar cells is the high efficiencywhich has currently crossed 20 Currently the best thin filmsolar cells have above 20 efficiency and are based on CIGS[46ndash49]

Recently quaternary compound Cu2ZnSn(SSe)

4has

been studied as a potential photovoltaic material due to itssimilarities with CIGS (Cu(InGa)Se

2) in material proper-

ties and the relative availability of raw materials CZTS is

Sunlight

TCOi-ZnOn-CdS

CZTS light absorberMo-coated substrate

Glass

Figure 4 Structure of CZTS solar cell [9]

a compound semiconductor in the form (I)2(II)(IV)(VI)

4 It

possesses a relatively high absorption coefficient (gt104 cmminus1)and a band gap of around 145 eV [47]Theoretically efficien-cies of around 32 have been calculated for CZTS thin filmsolar cells having a layer of CZTS several micrometers thick[46ndash49]

41 Basic Structure Schematic diagram of CZTS solar cellstructure is shown in Figure 4 Molybdenum thin film havingthickness of 500ndash700 nm is deposited on glass substrate andacts as a back contact Molybdenum has high stability inharsh reactive conditions such as sulphur-containing vaporand high temperaturesThe absorber layer p-type CZTS thinfilm is deposited on Mo layer having thickness in the rangeof 1-2 micrometers To form a p-n junction CdS layer havingthickness of 50ndash100 nm is coated on CZTS layer The CZTSsurface is uneven and cannot be completely covered by CdSthin filmThismay cause shorting between the front and backcontacts To avoid leakage 50ndash90 nm intrinsic ZnO thin filmis coated on CdS layer Then transparent conducting oxidethin film is deposited and acts as the front contact [47 48]

42 Fabrication of CZTS Devices421 Vacuum Techniques All the elements are simultane-ously incorporated in a single step in one-step vacuum pro-cessesThese techniques include cosputtering and coevapora-tion both of which give devices with good performance [48]Pulsed-laser deposition is a two-step process wherein the firststep incorporates the precursors in an ambient-temperatureprocess like sputtering or evaporation This is followed byannealing The incorporation of chalcogens can occur ineither step [47 48]

6 Journal of Applied Chemistry

Table 2 Comparison of CZTS cells fabricated by different processes

Method Precursor Efficiency () Comments

Vacuum thermalevaporation Cu Zn Sn S 84 [19]

Has been used commercially fast process compared tosputtering better purity high energy requirements tocreate vacuum difficulties in scaling up thicknesscontrol may be problematic

Sputtering Cu SnS ZnS 677 [20]Slower than evaporation scaling up is easier highercapital costs accounts for significant part ofcommercial production of CIGS cells vacuum processleading to higher energy requirements cost-effective

Electrodeposition Cu(II) ion Zn(II) ionSn(IV) ion 73 [21]

Generally more environmentally friendly usuallynontoxic for copper zinc tin electrodeposition iscarried out at room temperature reducing energyrequirements has been commercially used thicknesscontrol may be problematic

Sol-gel based method

Copper (II) acetatemonohydrate

Zinc (II) acetate dehydrateTin (II) chloride dehydrate

223 [22] Simple and versatile cost-effective environmentallyfriendly due to lower temperatures

Pulsed laser deposition In-house fabricated CZTSpellet 314 [23]

Vacuum process higher energy requirements scalingup difficulties composition and thickness dependenceon deposition conditions not yet well understood

422 Nonvacuum Techniques These processes include elec-trodeposition sol-gel based methods and spray coatingThey are scalable and cheaper which makes them suitablefor large-scale processes The highest efficiency of CZTSSecell (126) has been achieved by nonvacuum techniquessimultaneous use of spin-coating solution and particles ofconstituents Other promising methods are nanoparticlesand electroplating [47 48] Electrochemical deposition alsoappears to be a promising preparation method [47] Table 2shows a comparison of some of the processing techniques

5 Perovskites

Perovskites are materials described by the formula ABX3

where A B are cations A is bigger than B and X is an anionTheir structure is similar to the structure of calcium titanateFigure 5 shows the crystal structure of a typical perovskitestructured compound CH

3NH3Pb [10]

51 Hybrid Halide Perovskites In solar cells organic-inorganic halide perovskites are most commonly usedwhere A is an organic cation and X is a halide usually Iodinethough Cl and Br have also been used A is usually themethylammonium cation (CH

3NH3

+) However ethyl ammonium(CH3CH2NH3

+) and formamidinium (NH2CH=NH

2

+)are also used as cations Cl and Br are typically used in amixed halide material B is usually Pb or Sn due to bandgap considerations However due to the lower stability ofSn and the relative ease with which it is oxidized to SnI

4 Pb

is generally preferred Structure of methyl ammonium leadis shown in Figure 5 Lead has weak tendency to undergooxidization due to relativistic effects Therefore methylammonium lead triiodide is generally taken as the standardcompound though mixed halides CH

3NH3PbI3minusxClx and

CH3NH3PbI3minusxClx are also considered important Forma-

Figure 5 Structure of CH3NH3Pb [10]

midinium lead trihalide (H2NCHNH

2PbX3) has also shown

potential with band gaps in the range of 15 to 22 eV [50 51]The perovskite properties have been known for many

years However perovskite materials were first utilized ina photovoltaic device in 2009 This device was based ona dye-sensitized solar cell architecture using perovskiteas a sensitizer and achieved an efficiency of 38 forCH3NH3PbI3cells The main drawback was the cell stability

as the lifetime was in minutes In 2012 Snaith and hiscoworkers achieved a breakthrough with efficiencies goingabove 10 and demonstrated that perovskites played a role inthe transport of electrons and holes towards the cell terminallaying the basis for planar cells [52] Thus far research inperovskite cells has mainly concentrated on CH

3NH3PbI3

and CH3NH3PbI3minusxClx Currently high efficiencies over 20

have been achieved by perovskite devices [30] based on

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Analytical ChemistryInternational Journal of

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Quantum Chemistry

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CatalystsJournal of

Page 3: Review Article Emerging Photovoltaics: Organic, Copper ...

Journal of Applied Chemistry 3

Electrode 1

Electrode 2

Organic electronic material

(a)

Electrode 1

Electrode 2

Electron donor

Electron acceptor

(b)

Electrode 1

Electrode 2

Dispersed heterojunction

(c)

Figure 2 Schematics of different OPV cell structures (a) single layer device (b) bilayer device and (c) bulk heterojunction device

The process involves the following

(i) Generation of excitons(ii) Exciton diffusion(iii) Exciton dissociation(iv) Charge transport

The first step involves the absorption of photons fromlight and generation of electron-hole pair (exciton) Organicsemiconductors have high absorption coefficients Thereforea layer of thickness in the range of a few hundred nanometresis sufficient to absorb the incident light The absorbed lighttriggers the generation of electron-hole pairsThis is followedby exciton diffusion The excitons thus generated generallyhave lifetimes in the range of few picoseconds which limitstheir mobility The mobility of excitons is limited to a rangeof 10 nmThis is called exciton diffusion length and is crucialin the design and performance of organic solar cells Theexciton thus generated undergoes dissociation The electro-statically coupled electron-hole pair splits into free charges atthe donor-acceptor interface Ideally all the photogeneratedexcitons should reach a dissociation length However thisdoes not occur due to small exciton diffusion length limitingthe efficiency of the cell In the charge transport step the freecharges thus produced travel to the electrodes through thedonoracceptor materials fromwhere they enter the externalcircuit [12 36]

32 Device Structures The common basic OPV cell struc-tures include the following

321 Single Active Layer Cells Figure 2(a) illustrates thedevice structure of a single active layer cell Here a thinfilm of organic semiconductor is sandwiched between twoelectrodes A layer of high work function (eg IndiumTitaniumOxide (ITO)) and a layer having low work function(Mg Ag etc) are used as electrodes In practice these cellshave very low efficiencies (quantum efficiencies lt 1 andpower conversion efficiencies lt 01) and do not work verywell [12 36]

322 Bilayer Cells Two organic materials one acting as adonor and the second as an acceptor are sandwiched betweentwo electrodes (as shown in Figure 2(b)) Higher efficiency

of exciton dissociation makes these devices more efficientthan single layer devices These devices have achieved powerconversion efficiencies of around 36 using copper phthalo-cyanine and C

60[12 36]

323 Bulk Heterojunction Donor and acceptor materialsare mixed to form a bulk heterojunction Figure 2(c) showsstructure of the bulk heterojunction Bulk heterojunctionmaterials have many favourable properties including highphotosensitivity and energy conversion efficiency The pres-ence of illumination induces transfer of electrons fromdonor-type semiconducting conjugated polymer to acceptor-type conjugated polymers or molecules like Buckminster-fullerene C

60 Power conversion efficiencies of above 35

have been achieved using solution-cast P3HTPCBM blends[12 36]

324 Diffuse Bilayer Heterojunction This device structureaims to adapt the advantages of both the bilayer and bulkheterojunction devices It provides a larger donor-acceptorinterface area and a spatially uninterrupted pathway forcharge carriers [12]

33 Preparation of Organic Solar Cell Materials Two of thecommonly used techniques for materials synthesis are evap-oration and solution processing The choice of techniquesdepends upon the material to be used Thermal stability ofthe material has to be considered while using evaporationtechniques Similarly solubility of material is required forsolution processing The processing has significantly lowercosts as compared to inorganic materials and offers a greatdeal of versatility [12 36]

Polymer solar cells are usually fabricated by solutionprocessing at low temperatures as polymer molecules maydegrade at high temperatures Conjugated semiconductingpolymers are fabricated by printing and coating techniquessuch as spin-coating screen printing and doctor blading Ingeneral solution processes are preferred to vacuumprocessesdue to its lower energy requirements and cost effectiveness[12]

34 Potential Materials for Organic Solar Cells In organicsolar cells a layer of organic material acting as activelayer is sandwiched between two electrodes The organic

4 Journal of Applied Chemistry

N HN

N

N

NH

N

N

N

(a) Phthalocyanine

NH N

N HN

(b) Porphyrin (c) Fullerene [6]

S

S

S

S

S

S

(d) Polythiophene [7]

NH

O

O(e) Phthalimide [8]

Figure 3 Organic molecules used as electron donors and electron acceptors in organic solar cells

semiconductor must be either an electron donor or anelectron acceptor material The active layer consists of bothelectron donor and electron acceptor material [12]

341ElectronDonorMaterials Phthalocyanines (Figure 3(a))and their homologues have been commonly used as elec-tron donor materials Phthalocyanines (Pc) as shown inFigure 3(a) are 2D 18 pi electron aromatic porphyrin syntheticanalogues in which four isoindole units are joined by Natoms Also copper phthalocyanine and zinc phthalocyaninehave been used as donor materials Double heterojunc-tion CuPcC

60thin film cells with Ag cathode have given

efficiencies of about 4 [37 38] Further work on thesame CuPcC

60cell with hybrid planar-mixed molecular

heterojunctions has given efficiencies of around 55 [1214 36ndash40] Subphthalocyanines the lowest homologues ofphthalocyanines have shown promise due to their chemistryand properties CuPcC

60based cells have given greater

119881oc as compared to CuPcC60

based cells thus increasingefficiency [41] Porphyrins (Figure 3(b)) and their derivativeshave also been used as electron donors [12 14 36ndash40]These oligomer organic materials are however not alwayscompatible with the flexible electronics Most of them cannotbe obtained through solution processing and require thermal

evaporation techniques leading to increase in cost [12 14 36ndash38] Polymer-based organic solar cells can be obtained viasolution processing thus making them compatible with theflexible substrate and also reducing costs [42]

Polythiophene (Figure 3(d)) derivatives and fullerene(Figure 3(c)) derivatives have been blended together toformbulk heterojunction structures Poly(3-alkylthiophene)s(P3AT) in particular have shown great promise as elec-tron donor materials P3HT has given the best resultsP3HTPCBM ([66]-phenyl C

61-butyric acid methyl ester)

based devices have given efficiencies of around 5 [4042 43] Benzodithiophene derivatives have shown greatpromise for use in PSC and related areas Benzo(12-b 45-b1015840)dithiophene (BDT) has great potential for use in PSCs119881oc (open circuit voltage) and Jsc (short circuit current) ofBDT derivatives were 075 V and 38mAcm2 respectivelycorresponding to a PCE of 16 which indicates that BDT is apromising commonunit of photovoltaic conjugated polymers[43]

Recently phthalimide (Figure 3(e)) has emerged as anattractive candidate for electron-accepting unit in the donor-acceptor (D-A) copolymers due to its extremely facile syn-thesis and readily varied substitution at the imide nitro-gen allowing manipulation of polymer solubility packing

Journal of Applied Chemistry 5

Table 1 Power conversion efficiencies of some organic solar cells

Device configuration 119869sc (short circuitcurrent) in mA cmminus2

119881oc (open circuitvoltage) in V Fill factor PCE () Ref

ITOPFNPTB7PC71BMMoO

3Al 175 075 070 92 [14]

ITOZnO-PVPPDTS-TPDPC71BMMoO

3Ag 144 086 069 85 [15]

ITOTiPDPBDTTTCPC71BMMoO

3Ag 163 070 065 74 [16]

ITOPEDOTPSSPBnDTDTffBTPC61BMCaAl 129 091 061 72 [17]

ITOPEDOTPSSPIDT-phanQPC71BMC

60-bisAg 115 088 061 62 [18]

and morphology Two new D-A copolymers PDTSPhand PDTSBTPh based on dithienosilole donor unit andphthalimide acceptor unit were synthesized The powerconversion efficiency of the polymer solar cells based onPDTSBTPhPC

70BM (1 2 ww) reached 21 [44]

342 Electron Acceptor Materials Fullerenes (Figure 3(c))and their derivatives are the most commonly used acceptormaterials Fullerene can be reversibly reduced with up to6 electrons which has led to it being commonly used asan electron acceptor C

60has limited solubility in most

organic solvents To increase the solubility and to avoidsevere phase separation of DA blend [66]-phenyl C

60

butyric acid methyl ester (PC60BM) has been used as itcan be solution processed The PC70BM derivative has alsobeen studied but though it has stronger absorption in thevisible range it is more expensive than C

60due to the

purification processes [12 14 36ndash39] Indene-fullerenes havealso been used as electron acceptor materials specificallyindene-fullerene bisadduct (ICBA) and indene-fullerenemonoadduct (ICMA) These can be synthesized easily via aone-pot reaction ICBAP3HT and ICMAP3HT have givenhigher 119881oc than P3HTPCBM devices [12 14] Lately C

60

derivatives with oligo(phenyleneethynediyl) (OPE) subunitshave been studied [45]

SubPc has also been used an acceptor material Tetraceneas a donor and SubPc as an acceptor have been used and effi-ciencies have reached 29 Fluorinated subphthalocyanine(F16SubPc) also shows potential as electron donor [12]Table 1 gives a few materials and their efficiencies along

with the device type in an organic solar cell The highestefficiency for organic solar cells is around 11 (Toshiba) [31]

4 CZTS Solar Cells

The thin film solar cell technology is growing in both capacityand market share Currently it accounts for around 20 ofthe PV market [46] CdTe solar cells account for about 10and the remainder is divided between thin film silicon andCu(InGa)Se

2(CIGS) where CIGS is growing rapidly The

main advantage for CIGS solar cells is the high efficiencywhich has currently crossed 20 Currently the best thin filmsolar cells have above 20 efficiency and are based on CIGS[46ndash49]

Recently quaternary compound Cu2ZnSn(SSe)

4has

been studied as a potential photovoltaic material due to itssimilarities with CIGS (Cu(InGa)Se

2) in material proper-

ties and the relative availability of raw materials CZTS is

Sunlight

TCOi-ZnOn-CdS

CZTS light absorberMo-coated substrate

Glass

Figure 4 Structure of CZTS solar cell [9]

a compound semiconductor in the form (I)2(II)(IV)(VI)

4 It

possesses a relatively high absorption coefficient (gt104 cmminus1)and a band gap of around 145 eV [47]Theoretically efficien-cies of around 32 have been calculated for CZTS thin filmsolar cells having a layer of CZTS several micrometers thick[46ndash49]

41 Basic Structure Schematic diagram of CZTS solar cellstructure is shown in Figure 4 Molybdenum thin film havingthickness of 500ndash700 nm is deposited on glass substrate andacts as a back contact Molybdenum has high stability inharsh reactive conditions such as sulphur-containing vaporand high temperaturesThe absorber layer p-type CZTS thinfilm is deposited on Mo layer having thickness in the rangeof 1-2 micrometers To form a p-n junction CdS layer havingthickness of 50ndash100 nm is coated on CZTS layer The CZTSsurface is uneven and cannot be completely covered by CdSthin filmThismay cause shorting between the front and backcontacts To avoid leakage 50ndash90 nm intrinsic ZnO thin filmis coated on CdS layer Then transparent conducting oxidethin film is deposited and acts as the front contact [47 48]

42 Fabrication of CZTS Devices421 Vacuum Techniques All the elements are simultane-ously incorporated in a single step in one-step vacuum pro-cessesThese techniques include cosputtering and coevapora-tion both of which give devices with good performance [48]Pulsed-laser deposition is a two-step process wherein the firststep incorporates the precursors in an ambient-temperatureprocess like sputtering or evaporation This is followed byannealing The incorporation of chalcogens can occur ineither step [47 48]

6 Journal of Applied Chemistry

Table 2 Comparison of CZTS cells fabricated by different processes

Method Precursor Efficiency () Comments

Vacuum thermalevaporation Cu Zn Sn S 84 [19]

Has been used commercially fast process compared tosputtering better purity high energy requirements tocreate vacuum difficulties in scaling up thicknesscontrol may be problematic

Sputtering Cu SnS ZnS 677 [20]Slower than evaporation scaling up is easier highercapital costs accounts for significant part ofcommercial production of CIGS cells vacuum processleading to higher energy requirements cost-effective

Electrodeposition Cu(II) ion Zn(II) ionSn(IV) ion 73 [21]

Generally more environmentally friendly usuallynontoxic for copper zinc tin electrodeposition iscarried out at room temperature reducing energyrequirements has been commercially used thicknesscontrol may be problematic

Sol-gel based method

Copper (II) acetatemonohydrate

Zinc (II) acetate dehydrateTin (II) chloride dehydrate

223 [22] Simple and versatile cost-effective environmentallyfriendly due to lower temperatures

Pulsed laser deposition In-house fabricated CZTSpellet 314 [23]

Vacuum process higher energy requirements scalingup difficulties composition and thickness dependenceon deposition conditions not yet well understood

422 Nonvacuum Techniques These processes include elec-trodeposition sol-gel based methods and spray coatingThey are scalable and cheaper which makes them suitablefor large-scale processes The highest efficiency of CZTSSecell (126) has been achieved by nonvacuum techniquessimultaneous use of spin-coating solution and particles ofconstituents Other promising methods are nanoparticlesand electroplating [47 48] Electrochemical deposition alsoappears to be a promising preparation method [47] Table 2shows a comparison of some of the processing techniques

5 Perovskites

Perovskites are materials described by the formula ABX3

where A B are cations A is bigger than B and X is an anionTheir structure is similar to the structure of calcium titanateFigure 5 shows the crystal structure of a typical perovskitestructured compound CH

3NH3Pb [10]

51 Hybrid Halide Perovskites In solar cells organic-inorganic halide perovskites are most commonly usedwhere A is an organic cation and X is a halide usually Iodinethough Cl and Br have also been used A is usually themethylammonium cation (CH

3NH3

+) However ethyl ammonium(CH3CH2NH3

+) and formamidinium (NH2CH=NH

2

+)are also used as cations Cl and Br are typically used in amixed halide material B is usually Pb or Sn due to bandgap considerations However due to the lower stability ofSn and the relative ease with which it is oxidized to SnI

4 Pb

is generally preferred Structure of methyl ammonium leadis shown in Figure 5 Lead has weak tendency to undergooxidization due to relativistic effects Therefore methylammonium lead triiodide is generally taken as the standardcompound though mixed halides CH

3NH3PbI3minusxClx and

CH3NH3PbI3minusxClx are also considered important Forma-

Figure 5 Structure of CH3NH3Pb [10]

midinium lead trihalide (H2NCHNH

2PbX3) has also shown

potential with band gaps in the range of 15 to 22 eV [50 51]The perovskite properties have been known for many

years However perovskite materials were first utilized ina photovoltaic device in 2009 This device was based ona dye-sensitized solar cell architecture using perovskiteas a sensitizer and achieved an efficiency of 38 forCH3NH3PbI3cells The main drawback was the cell stability

as the lifetime was in minutes In 2012 Snaith and hiscoworkers achieved a breakthrough with efficiencies goingabove 10 and demonstrated that perovskites played a role inthe transport of electrons and holes towards the cell terminallaying the basis for planar cells [52] Thus far research inperovskite cells has mainly concentrated on CH

3NH3PbI3

and CH3NH3PbI3minusxClx Currently high efficiencies over 20

have been achieved by perovskite devices [30] based on

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 4: Review Article Emerging Photovoltaics: Organic, Copper ...

4 Journal of Applied Chemistry

N HN

N

N

NH

N

N

N

(a) Phthalocyanine

NH N

N HN

(b) Porphyrin (c) Fullerene [6]

S

S

S

S

S

S

(d) Polythiophene [7]

NH

O

O(e) Phthalimide [8]

Figure 3 Organic molecules used as electron donors and electron acceptors in organic solar cells

semiconductor must be either an electron donor or anelectron acceptor material The active layer consists of bothelectron donor and electron acceptor material [12]

341ElectronDonorMaterials Phthalocyanines (Figure 3(a))and their homologues have been commonly used as elec-tron donor materials Phthalocyanines (Pc) as shown inFigure 3(a) are 2D 18 pi electron aromatic porphyrin syntheticanalogues in which four isoindole units are joined by Natoms Also copper phthalocyanine and zinc phthalocyaninehave been used as donor materials Double heterojunc-tion CuPcC

60thin film cells with Ag cathode have given

efficiencies of about 4 [37 38] Further work on thesame CuPcC

60cell with hybrid planar-mixed molecular

heterojunctions has given efficiencies of around 55 [1214 36ndash40] Subphthalocyanines the lowest homologues ofphthalocyanines have shown promise due to their chemistryand properties CuPcC

60based cells have given greater

119881oc as compared to CuPcC60

based cells thus increasingefficiency [41] Porphyrins (Figure 3(b)) and their derivativeshave also been used as electron donors [12 14 36ndash40]These oligomer organic materials are however not alwayscompatible with the flexible electronics Most of them cannotbe obtained through solution processing and require thermal

evaporation techniques leading to increase in cost [12 14 36ndash38] Polymer-based organic solar cells can be obtained viasolution processing thus making them compatible with theflexible substrate and also reducing costs [42]

Polythiophene (Figure 3(d)) derivatives and fullerene(Figure 3(c)) derivatives have been blended together toformbulk heterojunction structures Poly(3-alkylthiophene)s(P3AT) in particular have shown great promise as elec-tron donor materials P3HT has given the best resultsP3HTPCBM ([66]-phenyl C

61-butyric acid methyl ester)

based devices have given efficiencies of around 5 [4042 43] Benzodithiophene derivatives have shown greatpromise for use in PSC and related areas Benzo(12-b 45-b1015840)dithiophene (BDT) has great potential for use in PSCs119881oc (open circuit voltage) and Jsc (short circuit current) ofBDT derivatives were 075 V and 38mAcm2 respectivelycorresponding to a PCE of 16 which indicates that BDT is apromising commonunit of photovoltaic conjugated polymers[43]

Recently phthalimide (Figure 3(e)) has emerged as anattractive candidate for electron-accepting unit in the donor-acceptor (D-A) copolymers due to its extremely facile syn-thesis and readily varied substitution at the imide nitro-gen allowing manipulation of polymer solubility packing

Journal of Applied Chemistry 5

Table 1 Power conversion efficiencies of some organic solar cells

Device configuration 119869sc (short circuitcurrent) in mA cmminus2

119881oc (open circuitvoltage) in V Fill factor PCE () Ref

ITOPFNPTB7PC71BMMoO

3Al 175 075 070 92 [14]

ITOZnO-PVPPDTS-TPDPC71BMMoO

3Ag 144 086 069 85 [15]

ITOTiPDPBDTTTCPC71BMMoO

3Ag 163 070 065 74 [16]

ITOPEDOTPSSPBnDTDTffBTPC61BMCaAl 129 091 061 72 [17]

ITOPEDOTPSSPIDT-phanQPC71BMC

60-bisAg 115 088 061 62 [18]

and morphology Two new D-A copolymers PDTSPhand PDTSBTPh based on dithienosilole donor unit andphthalimide acceptor unit were synthesized The powerconversion efficiency of the polymer solar cells based onPDTSBTPhPC

70BM (1 2 ww) reached 21 [44]

342 Electron Acceptor Materials Fullerenes (Figure 3(c))and their derivatives are the most commonly used acceptormaterials Fullerene can be reversibly reduced with up to6 electrons which has led to it being commonly used asan electron acceptor C

60has limited solubility in most

organic solvents To increase the solubility and to avoidsevere phase separation of DA blend [66]-phenyl C

60

butyric acid methyl ester (PC60BM) has been used as itcan be solution processed The PC70BM derivative has alsobeen studied but though it has stronger absorption in thevisible range it is more expensive than C

60due to the

purification processes [12 14 36ndash39] Indene-fullerenes havealso been used as electron acceptor materials specificallyindene-fullerene bisadduct (ICBA) and indene-fullerenemonoadduct (ICMA) These can be synthesized easily via aone-pot reaction ICBAP3HT and ICMAP3HT have givenhigher 119881oc than P3HTPCBM devices [12 14] Lately C

60

derivatives with oligo(phenyleneethynediyl) (OPE) subunitshave been studied [45]

SubPc has also been used an acceptor material Tetraceneas a donor and SubPc as an acceptor have been used and effi-ciencies have reached 29 Fluorinated subphthalocyanine(F16SubPc) also shows potential as electron donor [12]Table 1 gives a few materials and their efficiencies along

with the device type in an organic solar cell The highestefficiency for organic solar cells is around 11 (Toshiba) [31]

4 CZTS Solar Cells

The thin film solar cell technology is growing in both capacityand market share Currently it accounts for around 20 ofthe PV market [46] CdTe solar cells account for about 10and the remainder is divided between thin film silicon andCu(InGa)Se

2(CIGS) where CIGS is growing rapidly The

main advantage for CIGS solar cells is the high efficiencywhich has currently crossed 20 Currently the best thin filmsolar cells have above 20 efficiency and are based on CIGS[46ndash49]

Recently quaternary compound Cu2ZnSn(SSe)

4has

been studied as a potential photovoltaic material due to itssimilarities with CIGS (Cu(InGa)Se

2) in material proper-

ties and the relative availability of raw materials CZTS is

Sunlight

TCOi-ZnOn-CdS

CZTS light absorberMo-coated substrate

Glass

Figure 4 Structure of CZTS solar cell [9]

a compound semiconductor in the form (I)2(II)(IV)(VI)

4 It

possesses a relatively high absorption coefficient (gt104 cmminus1)and a band gap of around 145 eV [47]Theoretically efficien-cies of around 32 have been calculated for CZTS thin filmsolar cells having a layer of CZTS several micrometers thick[46ndash49]

41 Basic Structure Schematic diagram of CZTS solar cellstructure is shown in Figure 4 Molybdenum thin film havingthickness of 500ndash700 nm is deposited on glass substrate andacts as a back contact Molybdenum has high stability inharsh reactive conditions such as sulphur-containing vaporand high temperaturesThe absorber layer p-type CZTS thinfilm is deposited on Mo layer having thickness in the rangeof 1-2 micrometers To form a p-n junction CdS layer havingthickness of 50ndash100 nm is coated on CZTS layer The CZTSsurface is uneven and cannot be completely covered by CdSthin filmThismay cause shorting between the front and backcontacts To avoid leakage 50ndash90 nm intrinsic ZnO thin filmis coated on CdS layer Then transparent conducting oxidethin film is deposited and acts as the front contact [47 48]

42 Fabrication of CZTS Devices421 Vacuum Techniques All the elements are simultane-ously incorporated in a single step in one-step vacuum pro-cessesThese techniques include cosputtering and coevapora-tion both of which give devices with good performance [48]Pulsed-laser deposition is a two-step process wherein the firststep incorporates the precursors in an ambient-temperatureprocess like sputtering or evaporation This is followed byannealing The incorporation of chalcogens can occur ineither step [47 48]

6 Journal of Applied Chemistry

Table 2 Comparison of CZTS cells fabricated by different processes

Method Precursor Efficiency () Comments

Vacuum thermalevaporation Cu Zn Sn S 84 [19]

Has been used commercially fast process compared tosputtering better purity high energy requirements tocreate vacuum difficulties in scaling up thicknesscontrol may be problematic

Sputtering Cu SnS ZnS 677 [20]Slower than evaporation scaling up is easier highercapital costs accounts for significant part ofcommercial production of CIGS cells vacuum processleading to higher energy requirements cost-effective

Electrodeposition Cu(II) ion Zn(II) ionSn(IV) ion 73 [21]

Generally more environmentally friendly usuallynontoxic for copper zinc tin electrodeposition iscarried out at room temperature reducing energyrequirements has been commercially used thicknesscontrol may be problematic

Sol-gel based method

Copper (II) acetatemonohydrate

Zinc (II) acetate dehydrateTin (II) chloride dehydrate

223 [22] Simple and versatile cost-effective environmentallyfriendly due to lower temperatures

Pulsed laser deposition In-house fabricated CZTSpellet 314 [23]

Vacuum process higher energy requirements scalingup difficulties composition and thickness dependenceon deposition conditions not yet well understood

422 Nonvacuum Techniques These processes include elec-trodeposition sol-gel based methods and spray coatingThey are scalable and cheaper which makes them suitablefor large-scale processes The highest efficiency of CZTSSecell (126) has been achieved by nonvacuum techniquessimultaneous use of spin-coating solution and particles ofconstituents Other promising methods are nanoparticlesand electroplating [47 48] Electrochemical deposition alsoappears to be a promising preparation method [47] Table 2shows a comparison of some of the processing techniques

5 Perovskites

Perovskites are materials described by the formula ABX3

where A B are cations A is bigger than B and X is an anionTheir structure is similar to the structure of calcium titanateFigure 5 shows the crystal structure of a typical perovskitestructured compound CH

3NH3Pb [10]

51 Hybrid Halide Perovskites In solar cells organic-inorganic halide perovskites are most commonly usedwhere A is an organic cation and X is a halide usually Iodinethough Cl and Br have also been used A is usually themethylammonium cation (CH

3NH3

+) However ethyl ammonium(CH3CH2NH3

+) and formamidinium (NH2CH=NH

2

+)are also used as cations Cl and Br are typically used in amixed halide material B is usually Pb or Sn due to bandgap considerations However due to the lower stability ofSn and the relative ease with which it is oxidized to SnI

4 Pb

is generally preferred Structure of methyl ammonium leadis shown in Figure 5 Lead has weak tendency to undergooxidization due to relativistic effects Therefore methylammonium lead triiodide is generally taken as the standardcompound though mixed halides CH

3NH3PbI3minusxClx and

CH3NH3PbI3minusxClx are also considered important Forma-

Figure 5 Structure of CH3NH3Pb [10]

midinium lead trihalide (H2NCHNH

2PbX3) has also shown

potential with band gaps in the range of 15 to 22 eV [50 51]The perovskite properties have been known for many

years However perovskite materials were first utilized ina photovoltaic device in 2009 This device was based ona dye-sensitized solar cell architecture using perovskiteas a sensitizer and achieved an efficiency of 38 forCH3NH3PbI3cells The main drawback was the cell stability

as the lifetime was in minutes In 2012 Snaith and hiscoworkers achieved a breakthrough with efficiencies goingabove 10 and demonstrated that perovskites played a role inthe transport of electrons and holes towards the cell terminallaying the basis for planar cells [52] Thus far research inperovskite cells has mainly concentrated on CH

3NH3PbI3

and CH3NH3PbI3minusxClx Currently high efficiencies over 20

have been achieved by perovskite devices [30] based on

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

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[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

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[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

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Journal of

Chemistry

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Advances in

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Analytical Methods in Chemistry

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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

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Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Theoretical ChemistryJournal of

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Analytical ChemistryInternational Journal of

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Quantum Chemistry

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CatalystsJournal of

Page 5: Review Article Emerging Photovoltaics: Organic, Copper ...

Journal of Applied Chemistry 5

Table 1 Power conversion efficiencies of some organic solar cells

Device configuration 119869sc (short circuitcurrent) in mA cmminus2

119881oc (open circuitvoltage) in V Fill factor PCE () Ref

ITOPFNPTB7PC71BMMoO

3Al 175 075 070 92 [14]

ITOZnO-PVPPDTS-TPDPC71BMMoO

3Ag 144 086 069 85 [15]

ITOTiPDPBDTTTCPC71BMMoO

3Ag 163 070 065 74 [16]

ITOPEDOTPSSPBnDTDTffBTPC61BMCaAl 129 091 061 72 [17]

ITOPEDOTPSSPIDT-phanQPC71BMC

60-bisAg 115 088 061 62 [18]

and morphology Two new D-A copolymers PDTSPhand PDTSBTPh based on dithienosilole donor unit andphthalimide acceptor unit were synthesized The powerconversion efficiency of the polymer solar cells based onPDTSBTPhPC

70BM (1 2 ww) reached 21 [44]

342 Electron Acceptor Materials Fullerenes (Figure 3(c))and their derivatives are the most commonly used acceptormaterials Fullerene can be reversibly reduced with up to6 electrons which has led to it being commonly used asan electron acceptor C

60has limited solubility in most

organic solvents To increase the solubility and to avoidsevere phase separation of DA blend [66]-phenyl C

60

butyric acid methyl ester (PC60BM) has been used as itcan be solution processed The PC70BM derivative has alsobeen studied but though it has stronger absorption in thevisible range it is more expensive than C

60due to the

purification processes [12 14 36ndash39] Indene-fullerenes havealso been used as electron acceptor materials specificallyindene-fullerene bisadduct (ICBA) and indene-fullerenemonoadduct (ICMA) These can be synthesized easily via aone-pot reaction ICBAP3HT and ICMAP3HT have givenhigher 119881oc than P3HTPCBM devices [12 14] Lately C

60

derivatives with oligo(phenyleneethynediyl) (OPE) subunitshave been studied [45]

SubPc has also been used an acceptor material Tetraceneas a donor and SubPc as an acceptor have been used and effi-ciencies have reached 29 Fluorinated subphthalocyanine(F16SubPc) also shows potential as electron donor [12]Table 1 gives a few materials and their efficiencies along

with the device type in an organic solar cell The highestefficiency for organic solar cells is around 11 (Toshiba) [31]

4 CZTS Solar Cells

The thin film solar cell technology is growing in both capacityand market share Currently it accounts for around 20 ofthe PV market [46] CdTe solar cells account for about 10and the remainder is divided between thin film silicon andCu(InGa)Se

2(CIGS) where CIGS is growing rapidly The

main advantage for CIGS solar cells is the high efficiencywhich has currently crossed 20 Currently the best thin filmsolar cells have above 20 efficiency and are based on CIGS[46ndash49]

Recently quaternary compound Cu2ZnSn(SSe)

4has

been studied as a potential photovoltaic material due to itssimilarities with CIGS (Cu(InGa)Se

2) in material proper-

ties and the relative availability of raw materials CZTS is

Sunlight

TCOi-ZnOn-CdS

CZTS light absorberMo-coated substrate

Glass

Figure 4 Structure of CZTS solar cell [9]

a compound semiconductor in the form (I)2(II)(IV)(VI)

4 It

possesses a relatively high absorption coefficient (gt104 cmminus1)and a band gap of around 145 eV [47]Theoretically efficien-cies of around 32 have been calculated for CZTS thin filmsolar cells having a layer of CZTS several micrometers thick[46ndash49]

41 Basic Structure Schematic diagram of CZTS solar cellstructure is shown in Figure 4 Molybdenum thin film havingthickness of 500ndash700 nm is deposited on glass substrate andacts as a back contact Molybdenum has high stability inharsh reactive conditions such as sulphur-containing vaporand high temperaturesThe absorber layer p-type CZTS thinfilm is deposited on Mo layer having thickness in the rangeof 1-2 micrometers To form a p-n junction CdS layer havingthickness of 50ndash100 nm is coated on CZTS layer The CZTSsurface is uneven and cannot be completely covered by CdSthin filmThismay cause shorting between the front and backcontacts To avoid leakage 50ndash90 nm intrinsic ZnO thin filmis coated on CdS layer Then transparent conducting oxidethin film is deposited and acts as the front contact [47 48]

42 Fabrication of CZTS Devices421 Vacuum Techniques All the elements are simultane-ously incorporated in a single step in one-step vacuum pro-cessesThese techniques include cosputtering and coevapora-tion both of which give devices with good performance [48]Pulsed-laser deposition is a two-step process wherein the firststep incorporates the precursors in an ambient-temperatureprocess like sputtering or evaporation This is followed byannealing The incorporation of chalcogens can occur ineither step [47 48]

6 Journal of Applied Chemistry

Table 2 Comparison of CZTS cells fabricated by different processes

Method Precursor Efficiency () Comments

Vacuum thermalevaporation Cu Zn Sn S 84 [19]

Has been used commercially fast process compared tosputtering better purity high energy requirements tocreate vacuum difficulties in scaling up thicknesscontrol may be problematic

Sputtering Cu SnS ZnS 677 [20]Slower than evaporation scaling up is easier highercapital costs accounts for significant part ofcommercial production of CIGS cells vacuum processleading to higher energy requirements cost-effective

Electrodeposition Cu(II) ion Zn(II) ionSn(IV) ion 73 [21]

Generally more environmentally friendly usuallynontoxic for copper zinc tin electrodeposition iscarried out at room temperature reducing energyrequirements has been commercially used thicknesscontrol may be problematic

Sol-gel based method

Copper (II) acetatemonohydrate

Zinc (II) acetate dehydrateTin (II) chloride dehydrate

223 [22] Simple and versatile cost-effective environmentallyfriendly due to lower temperatures

Pulsed laser deposition In-house fabricated CZTSpellet 314 [23]

Vacuum process higher energy requirements scalingup difficulties composition and thickness dependenceon deposition conditions not yet well understood

422 Nonvacuum Techniques These processes include elec-trodeposition sol-gel based methods and spray coatingThey are scalable and cheaper which makes them suitablefor large-scale processes The highest efficiency of CZTSSecell (126) has been achieved by nonvacuum techniquessimultaneous use of spin-coating solution and particles ofconstituents Other promising methods are nanoparticlesand electroplating [47 48] Electrochemical deposition alsoappears to be a promising preparation method [47] Table 2shows a comparison of some of the processing techniques

5 Perovskites

Perovskites are materials described by the formula ABX3

where A B are cations A is bigger than B and X is an anionTheir structure is similar to the structure of calcium titanateFigure 5 shows the crystal structure of a typical perovskitestructured compound CH

3NH3Pb [10]

51 Hybrid Halide Perovskites In solar cells organic-inorganic halide perovskites are most commonly usedwhere A is an organic cation and X is a halide usually Iodinethough Cl and Br have also been used A is usually themethylammonium cation (CH

3NH3

+) However ethyl ammonium(CH3CH2NH3

+) and formamidinium (NH2CH=NH

2

+)are also used as cations Cl and Br are typically used in amixed halide material B is usually Pb or Sn due to bandgap considerations However due to the lower stability ofSn and the relative ease with which it is oxidized to SnI

4 Pb

is generally preferred Structure of methyl ammonium leadis shown in Figure 5 Lead has weak tendency to undergooxidization due to relativistic effects Therefore methylammonium lead triiodide is generally taken as the standardcompound though mixed halides CH

3NH3PbI3minusxClx and

CH3NH3PbI3minusxClx are also considered important Forma-

Figure 5 Structure of CH3NH3Pb [10]

midinium lead trihalide (H2NCHNH

2PbX3) has also shown

potential with band gaps in the range of 15 to 22 eV [50 51]The perovskite properties have been known for many

years However perovskite materials were first utilized ina photovoltaic device in 2009 This device was based ona dye-sensitized solar cell architecture using perovskiteas a sensitizer and achieved an efficiency of 38 forCH3NH3PbI3cells The main drawback was the cell stability

as the lifetime was in minutes In 2012 Snaith and hiscoworkers achieved a breakthrough with efficiencies goingabove 10 and demonstrated that perovskites played a role inthe transport of electrons and holes towards the cell terminallaying the basis for planar cells [52] Thus far research inperovskite cells has mainly concentrated on CH

3NH3PbI3

and CH3NH3PbI3minusxClx Currently high efficiencies over 20

have been achieved by perovskite devices [30] based on

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CatalystsJournal of

Page 6: Review Article Emerging Photovoltaics: Organic, Copper ...

6 Journal of Applied Chemistry

Table 2 Comparison of CZTS cells fabricated by different processes

Method Precursor Efficiency () Comments

Vacuum thermalevaporation Cu Zn Sn S 84 [19]

Has been used commercially fast process compared tosputtering better purity high energy requirements tocreate vacuum difficulties in scaling up thicknesscontrol may be problematic

Sputtering Cu SnS ZnS 677 [20]Slower than evaporation scaling up is easier highercapital costs accounts for significant part ofcommercial production of CIGS cells vacuum processleading to higher energy requirements cost-effective

Electrodeposition Cu(II) ion Zn(II) ionSn(IV) ion 73 [21]

Generally more environmentally friendly usuallynontoxic for copper zinc tin electrodeposition iscarried out at room temperature reducing energyrequirements has been commercially used thicknesscontrol may be problematic

Sol-gel based method

Copper (II) acetatemonohydrate

Zinc (II) acetate dehydrateTin (II) chloride dehydrate

223 [22] Simple and versatile cost-effective environmentallyfriendly due to lower temperatures

Pulsed laser deposition In-house fabricated CZTSpellet 314 [23]

Vacuum process higher energy requirements scalingup difficulties composition and thickness dependenceon deposition conditions not yet well understood

422 Nonvacuum Techniques These processes include elec-trodeposition sol-gel based methods and spray coatingThey are scalable and cheaper which makes them suitablefor large-scale processes The highest efficiency of CZTSSecell (126) has been achieved by nonvacuum techniquessimultaneous use of spin-coating solution and particles ofconstituents Other promising methods are nanoparticlesand electroplating [47 48] Electrochemical deposition alsoappears to be a promising preparation method [47] Table 2shows a comparison of some of the processing techniques

5 Perovskites

Perovskites are materials described by the formula ABX3

where A B are cations A is bigger than B and X is an anionTheir structure is similar to the structure of calcium titanateFigure 5 shows the crystal structure of a typical perovskitestructured compound CH

3NH3Pb [10]

51 Hybrid Halide Perovskites In solar cells organic-inorganic halide perovskites are most commonly usedwhere A is an organic cation and X is a halide usually Iodinethough Cl and Br have also been used A is usually themethylammonium cation (CH

3NH3

+) However ethyl ammonium(CH3CH2NH3

+) and formamidinium (NH2CH=NH

2

+)are also used as cations Cl and Br are typically used in amixed halide material B is usually Pb or Sn due to bandgap considerations However due to the lower stability ofSn and the relative ease with which it is oxidized to SnI

4 Pb

is generally preferred Structure of methyl ammonium leadis shown in Figure 5 Lead has weak tendency to undergooxidization due to relativistic effects Therefore methylammonium lead triiodide is generally taken as the standardcompound though mixed halides CH

3NH3PbI3minusxClx and

CH3NH3PbI3minusxClx are also considered important Forma-

Figure 5 Structure of CH3NH3Pb [10]

midinium lead trihalide (H2NCHNH

2PbX3) has also shown

potential with band gaps in the range of 15 to 22 eV [50 51]The perovskite properties have been known for many

years However perovskite materials were first utilized ina photovoltaic device in 2009 This device was based ona dye-sensitized solar cell architecture using perovskiteas a sensitizer and achieved an efficiency of 38 forCH3NH3PbI3cells The main drawback was the cell stability

as the lifetime was in minutes In 2012 Snaith and hiscoworkers achieved a breakthrough with efficiencies goingabove 10 and demonstrated that perovskites played a role inthe transport of electrons and holes towards the cell terminallaying the basis for planar cells [52] Thus far research inperovskite cells has mainly concentrated on CH

3NH3PbI3

and CH3NH3PbI3minusxClx Currently high efficiencies over 20

have been achieved by perovskite devices [30] based on

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 7: Review Article Emerging Photovoltaics: Organic, Copper ...

Journal of Applied Chemistry 7

Table 3 A few representative devices architecture fill factors and their efficiencies

Architecture Type HTM 119881oc (V) FF PCE () RefmpTiO

2MAPbI

3HTM MS Spiro-OMeTAD 099 073 15 [24]

YTiO2MAPbI

3minus119909Cl119909HTM P Spiro-OMeTAD 113 075 193 [25]

mpTiO2MAPbI

3HTM MS CuSCN 101 062 124 [26]

TiO2MAPbI

3minus119909Cl119909HTM P CuSCN 073 062 64 [27]

HTMMAPbI3minus119909

Cl119909PC61BMZnO P Graphene oxide 099 072 111 [28]

mpTiO2MAPbI

3HTM MS P3HT 073 073 67 [29]

P refers to devices with planar architecture and MS refers to devices with mesoporous architecture

Cathode

p-type contact

n-type contact

Anode

mp-TiO2 + perovskite

(a)

Cathode

p-type contact

n-type contact

Anode

Perovskite

(b)

Figure 6 Perovskite device structures with (a) mesoporous architecture and (b) planar architecture

a mesoporous TiO2structure It is expected that higher

efficiencies can be possible utilizing a tandem structure

52 Device Architecture Perovskite solar cells work effi-ciently in various architectures depending on the role playedby the perovskite material in the device or the nature ofthe electrodes It can broadly be divided into mesoporousnanostructure (similar to dye-sensitized solar cells) (a) orplanar structure (thin film) (b) [30 53] A wide range oftechniques are available for the fabrication of devices of eitherarchitecture

521MesoporousArchitecture Initially the organic-inorgan-ic perovskites were used as sensitizers for liquid-state DSSCs(dye-sensitized solar cells) as nanoparticles on the surface ofa mesoporous metal oxide film (Figure 6(a)) When coupledwith an iodide-triiodide liquid electrolyte the cells gavereasonably high PCEs but had poor stability due to thedissolution of the perovskite film A major breakthroughwas made in 2012 by coupling the perovskite with a smallorganic molecule 221015840771015840-tetrakis(NN-di-p-methoxy-phe-nyl-amine)-991015840-spirobiflourene (spiro-OMeTAD) whichwould act as hole transport material (HTM) A PCE of upto 97 was obtained using CH

3NH3PbI3devices with a

titanium oxide (TiO2) scaffold [54] Transient absorption

studies showed that TiO2plays a role in the photoconversion

process TiO2is therefore considered an active component

in the solar cell TiO2along with metal oxides with similar

functions is considered active scaffolds Around the sametime a PCE of 109 was achieved using a mixed halideperovskite CH

3NH3PbI3minusxClx deposited on insulating

Al2O3scaffold and coupled with spiro-OMeTAD These

types of cells are known as meso-superstructured solar cells(MSSCs) The metal oxides in MSSCs act as a scaffold butdo not take active part in the charge transport They areconsidered to be passive scaffolding [54] This architectureis based on DSSCs Perovskite is mainly used for lightabsorption and other materials are used for the chargetransport The perovskite light absorber forms a coating onthe mesoporous scaffolding [30 53]

522 Planar Heterojunction Architecture In this architecture(as shown in Figure 6(b)) a semiconducting absorbermaterialis usually sandwiched between two selective contacts withouta mesoporous scaffold Here there is a more noticeableinterface between layers Charge-selective transporting orblocking layers can be used in planar devices This architec-ture is somewhat similar to thin film solar cells [30 53 54]

Table 3 shows a few representative devices and theirarchitectures and performance

53 Fabrication Techniques Compared to conventional sil-icon solar cells perovskite cells can be manufactured withrelatively simpler techniques Many different techniques areavailable for synthesizing perovskite active layers includingthe following

(1) One-step precursor solution deposition(2) Dual-source vapor deposition(3) Vapor assisted solution process(4) Sequential vapor deposition

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 8: Review Article Emerging Photovoltaics: Organic, Copper ...

8 Journal of Applied Chemistry

Table 4 A comparison of common fabrication techniques

Method Description Advantages Disadvantages

One-step solutiondeposition

A solution of the organic andinorganic components dissolvedin a solvent is spin-coated on asubstrate to give perovskite

Cost-effective straightforward toimplement

Poor film formation leads to limitedefficiency choice of a solvent that cansimultaneously dissolve bothcomponents is limited spin-coating isinherently a batch process which maylimit production speed

Two-stepsolution-basedprocessing

First a solution of the inorganiccomponent is spin-coatedfollowed by spin-coating of asolution of the organiccomponent

Better photovoltaic performancecompared to one-step methods

Less control over film thickness ascompared to vacuum processes

Dual-source vapordeposition

The organic and inorganiccomponents are coevaporated inan as-deposited ratio depositionis followed by thermal annealing

Better film uniformity ascompared to solution processesleading to better efficiencies

Vacuum process which leads to highenergy requirements difficulties insimultaneously controlling thedeposition rates of both componentsleading to an undesirablestoichiometric film

Sequential vapordeposition

A bilayer film of the inorganicand organic components isprepared by sequentialdeposition subsequent vacuumdeposition of the organiccomponent is followed bythermal annealing

Eliminates problems of one-stepcodeposition

Vacuum process which leads to highenergy requirements higher costslimiting mass production

Vapor assistedsolution process

Inorganic component isdeposited by spin-coatingfollowed by exposure to thevapor of the organic componentat an elevated temperature

Combination of vapor andsolution-based processes givesbetter film quality

Electrodeposition

The inorganic film iselectrochemically depositedfollowed by a solid state in situreaction with inorganic layer togive perovskite

Environmentally friendly usuallynontoxic has been commerciallyused

Scaling up of these processes seems to be relatively feasible[53 55]

Perovskites can be easily incorporated into the existingphotovoltaic architectures The best perovskite structuresuse vacuum deposition to give more uniform film quali-ties However this necessitates the accurate coevaporationof the organic and inorganic components simultaneouslyThis will require specialist evaporation chambers A muchsimpler alternative is provided by the development of lowtemperature solution deposition techniques which can becarried out with existing material sets Perovskite solar cellswere initially developed out of DSSC research However nowmany perovskite device architectures are similar to thin filmphotovoltaics except with perovskite as active layers

The major issue for practical device fabrication is of thefilm thickness and qualityThe active perovskite layermust beseveral hundred nanometres thick muchmore than for mostorganic photovoltaics Even with optimization of depositionconditions and annealing temperature a significant amountof surface roughness remains thus requiring the thicknessof interface layers to be greater than what might normallybe used However efficiencies of around 11 have been

achieved by spin-coated devices [46 47 49] Table 4 shows acomparison of some of the common fabrication techniques

6 Comparison of Organic CZTS andPerovskite-Based Devices

61 Performances The main considerations for successfulcommercialization of these technologies are efficienciescosts and lifetimes Other factors to be considered includetoxicmaterials used in themanufacturing processes environ-mentally friendly production and the possibility of flexibleaesthetically pleasing products

Organic solar cells have efficiencies lower than theirinorganic counterparts While improvement is warrantedtheir low efficiencies are balanced by the fact that they aremuch cheaper to produce The highest organic cell efficiencyof 110 is claimed by Toshiba using a p-type semiconductormaterial and a structure called ldquoinverted structurerdquo [31]

In case of CZTS devices a world record conversionefficiency of 126 by IBM obtained for Cu

2ZnSn(SSe)

4

solar cells was made by solution-based method The methodintroduced Selenium a rare element into the CZTS TFSC

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 9: Review Article Emerging Photovoltaics: Organic, Copper ...

Journal of Applied Chemistry 9

Table 5 Highest efficiencies of solar cells [30]

Device Efficiency () Area (cm2) 119881oc (V) OCvoltage

119869sc mAcm2short circuitcurrent

Description

Organic thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

110 plusmn 03 0993 (da) 0793 1940 Toshiba [31]

Organic (mini module)(measured under the global AM15 spectrum (1000Wm2) at25∘C)

97 plusmn 03 2614 (da) 0686 1147Toshiba

(eight-seriescells)

CZTSSe (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

126 plusmn 03 04209 (ap) 05134 3521 IBM solutiongrown [32]

CZTS (thin film) (not measuredunder the global AM 15spectrum (1000Wmminus2) at 25∘C)

91 plusmn 02 02409 (da) 0701 2064 Toyota CentralRampD Labs [33]

Perovskite (thin film) (notmeasured under the global AM15 spectrum (1000Wmminus2) at25∘C)

201 plusmn 04 00955 (ap) 1059 2465 KRICT [34]

Perovskite thin film (measuredunder the global AM 15spectrum (1000Wm2) at 25∘C)

150 plusmn 06 1017 (ap) 1090 2061 NIMS [35]

da designated illumination area ap aperture area

However hydrazine solvent was used a toxic and instablesolvent [55]

The efficiencies of perovskite solar cell devices haveincreased drastically from 38 [52] in 2009 to 2102 in2015 thus making it one of the fastest growing emerging PVtechnologies Perovskite cells have thus reached efficienciescomparable to multicrystalline silicon and CIGS (efficienciesaround 20) [55] The 2102 efficiency has been achievedat EPFL Other perovskite solar cells have also reachedcomparable efficiencies [52]

The highest efficiencies of these cells are given in Table 5

62 Advantages and Disadvantages Organic semiconduc-tors promise to be much cheaper than their inorganiccounterparts due to low-cost processing They show greatversatility in production methods including methods likesolution processes and high throughput printing techniquesto name a few These methods require much less energy andlower temperatures compared to conventional methods andreduce the cost drastically Environmentally friendly cheapermaterials and production are another advantage

The organic molecule properties can be ldquotailoredrdquodepending upon the applications This is a very importantadvantage Due to tailoring of molecule properties and low-cost versatile production techniques organic solar cells canbe incredibly flexible and lightweight They can be manufac-tured in extremely thin lightweight flexible and aestheticallypleasing forms unlike conventional solar cells Colourfulsemitransparent solar cells are possible Organic solar cellsusually have much lower efficiencies as compared to siliconcellsThey usually have a shorter operational lifetime limited

by oxygen and UV radiation However lifetimes of OPVdevices by Heliatek have been extrapolated to over 20 years(Heliatek) Despite these limitations organic solar cells showgreat promise and are gaining rapid acceptance in the solarphotovoltaics industries

CZTS solar cells aremainly being studied as an alternativeto CIGS and CdTe devices CZTS TFSCs have an importantadvantage over CIGS solar cells The elements used in CZTSdevices namely copper tin zinc and sulphur are nontoxicenvironmentally friendly and abundant Indium and Gal-lium which are used in CIGS devices are both expensiveThe cost of raw materials for CZTS TFSCs is significantlylower than that of the three thin film technologies currentlyin use namely crystal Si CdTe and CIGS Selenium has beenused in CZTS TFSCs along with sulphur but although it israrer than Indium or Gallium it is much cheaper The CZTSdevices can also be manufactured using the vacuum coatingtechniques used in CIGS devices Their efficiencies are lesssensitive to changes in temperatures which makes themfavourable for higher temperature applications They alsooffer longer lifetimes than the other two devices mentionedhere

Efforts are being made to replace Selenium with sulphurSelenium is not very toxic but its compounds such as hydro-gen selenide are highly toxic The CZTSSe device currentlyhas higher efficiencies than the CZTS cell [47] The CZTSdevice usually incorporates CdS filmThe p-type CZTS layeris the absorber and the CdS is used as the n-type Cd istoxic and legal restrictions on the use of Cd in electronicdevices could cause problems Efforts are being made toeliminate the CdS layer from CZTS devices [47] In addition

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 10: Review Article Emerging Photovoltaics: Organic, Copper ...

10 Journal of Applied Chemistry

Table 6 Comparison of cost and manufacturing process

Devices Cost of raw material Cost ofmanufacturing Method of manufacturing Other properties

Organic Low LowEnvironmentally friendly

requires low temperature andenergy

Can be tailored according toapplication thin and lightweight shorter lifetime

CZTS Higher than organic High Uses toxic solvents

Suitable for high temperatureapplications efficiency less

sensitive to temperature longerlifetime

Perovskite Higher than organic Low Low temperature solution-basedfabrication toxic due to lead (Pb)

High stability in air sensitive tomoisture high efficiency but

degrades under normalconditions working principle as

yet unestablished

the efficiencies of CZTS devices are still about half that ofCZTS and CdTe devices (around 20) [30] However CZTStechnology is still at a much earlier stage of development

Despite these challenges due to availability of raw mate-rials and environmentally friendly features CZTS continuesto be a promising avenue of research and is likely to becomecommercially viable

The perovskite-based devices have shown unprecedentedefficiencies in a very short period It seems likely thatperovskite-based devices will soon overtake the establishedthin film technologies (CdTe and CIGS) Its advantages overother PV devices include its low temperature solution-basedfabrication method leading to lower manufacturing costshigher stability in air and higher absorption coefficientsTypically it gives relatively higher values of119881oc (gt11 V) Alsoits efficiency is aided by the higher diffusion length andhighermobilities of the charge carriers

However the use of lead poses a problem due to toxicityconcerns Elimination of lead in favour of Sn is a promisingpossibility [53] Also the sensitivity of perovskites towardsmoisture necessitates them to be well sealed to prevent theirpremature degradation There is insufficient data regardinglifetimesThematerials undergo degradation under standardconditions and show drop in efficiencies

Nevertheless inorganic-organic halide perovskite solarcells have demonstrated great potential due to their high effi-ciencies and low-cost manufacturing Since this technologyis relatively new there are many opportunities for furtherresearch and study

Table 6 shows comparison between all the three types ofsolar cells

7 Conclusion

Many different approaches are being studied to increase theefficiencies of solar cell devices The photovoltaic materialscovered in this paper are still mostly in the research anddevelopment stage However as the global energy crisiscontinues research in solar cells continues to gain tractionWith the evolution of material technology over the next fewyears the practical implementation of these approaches islikely to become feasible

Successful commercialization of these technologiesdepends mainly on three things cost efficiency andlifetime While organic solar cells have lower efficiencies(currently around 10) and shorter lifetimes in comparisonto inorganic devices the versatility they offer in terms ofprocessing and the low-cost manufacturing makes theman attractive prospect Manufacturing of organic solarcells remains much cheaper and simpler in comparisonto inorganic devices The possibility of manufacturing ofcolourful flexible aesthetically pleasing solar cells is also anadded advantage [36]

CZTS devices have lower efficiencies in general (around9) unless Selenium is incorporated However Se beinga rare element costs more and this could limit its large-scale development However the elimination of Se in favourof S remains an option Even so as technology continuesto mature CZTS appears to be a good alternative to theCIGS solar cell With the relative abundance of its elementsthe environmentally friendly features and reasonably goodperformance CZTS appears to be a promising avenue forfurther study

Perovskite solar cells have shown rapid growth in the past5 years These devices have shown unprecedented increasein efficiencies from 97 in 2012 to around 20 currentlyand have become comparable with thin film technologies likeCIGS and CdTe As yet the working principle behind theperovskite photovoltaic devices has not yet been establishedPerovskite cells offer a diverse range of production methodsand the possibility of manufacturing aesthetically pleasingsolar cells Currently the use of lead in these devices isnot an obstacle to large-scale applications However asthe use of toxic materials is likely to become increasinglyrestricted replacement of lead with tin is being studied [53]As interest in perovskite-based technology continues to growcommercialization of this technology seems very likely

To summarize this article provides a basic understandingof principle of a solar cell and an overview of variousdevelopments in this field over the last few decades It gives acomparison of the fabrication techniques for various devicesIn particular it presents a review of the progress in devel-opment of solar cells of third generation and compares theirefficiency cost effectiveness and also their future commercialprospects

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 11: Review Article Emerging Photovoltaics: Organic, Copper ...

Journal of Applied Chemistry 11

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M A Green ldquoThe path to 25 silicon solar cell efficiencyhistory of silicon cell evolutionrdquo Progress in PhotovoltaicsResearch and Applications vol 17 no 3 pp 183ndash189 2009

[2] T Saga ldquoAdvances in crystalline silicon solar cell technology forindustrial mass productionrdquo NPG Asia Materials vol 2 no 3pp 96ndash102 2010

[3] S Sharma K K Jain and A Sharma ldquoSolar cells in researchand applicationsmdasha reviewrdquo Materials Sciences and Applica-tions vol 06 no 12 pp 1145ndash1155 2015

[4] G Niu X Guo and L Wang ldquoReview of recent progress inchemical stability of perovskite solar cellsrdquo Journal of MaterialsChemistry A vol 3 no 17 pp 8970ndash8980 2015

[5] httppveducationcom[6] National Center for Biotechnology Information PubChem

Compound Database CID=123591 httpspubchemncbinlmnihgovcompound123591

[7] National Center for Biotechnology Information PubChemCompound Database CID=6809 httpspubchemncbinlmnihgovcompound6809

[8] Bryan Derksen wikipedia[9] NREL httpwwwnrelgovncpv[10] C Eames J M Frost P R F Barnes B C OrsquoRegan A Walsh

and M Saiful Islam ldquoIonic transport in hybrid lead iodideperovskite solar cellsrdquo Nature Communications vol 6 article7497 2015

[11] H Spanggaard and F C Krebs ldquoA brief history of the devel-opment of organic and polymeric photovoltaicsrdquo Solar EnergyMaterials amp Solar Cells vol 83 no 2-3 pp 125ndash146 2004

[12] H Hoppe and N S Sariciftci ldquoOrganic solar cells an overviewrdquoJournal of Materials Research vol 19 no 7 pp 1924ndash1945 2004

[13] J C Bernede ldquoOrganic photovoltaic cells history principle andtechniquesrdquo Journal of Chilean Chemical Society vol 53 no 3pp 1549ndash1564 2008

[14] Z He C Zhong S Su M Xu H Wu and Y Cao ldquoEnhancedpower-conversion efficiency in polymer solar cells using aninverted device structurerdquo Nature Photonics vol 6 no 9 pp591ndash595 2012

[15] C E Small S Chen J Subbiah et al ldquoHigh-efficiencyinverted dithienogermole-thienopyrrolodione-based polymersolar cellsrdquo Nature Photonics vol 6 no 2 pp 115ndash120 2012

[16] Z Tan W Zhang Z Zhang et al ldquoHigh-performance invertedpolymer solar cells with solution-processed titanium chelate aselectron-collecting layer on ITO electroderdquo Advanced Materi-als vol 24 no 11 pp 1476ndash1481 2012

[17] H Zhou L Yang A C Stuart S C Price S Liu and W YouldquoDevelopment of fluorinated benzothiadiazole as a structuralunit for a polymer solar cell of 7 efficiencyrdquo AngewandteChemie International Edition vol 50 no 13 pp 2995ndash29982011

[18] KM OrsquoMalley C-Z Li H-L Yip and A K-Y Jen ldquoEnhancedopen-circuit voltage in high performance polymerfullerenebulk-heterojunction solar cells by cathode modification with aC60surfactantrdquoAdvanced Energy Materials vol 2 no 1 pp 82ndash

86 2012

[19] B Shin O Gunawan Y Zhu N A Bojarczuk S J Chey andS Guha ldquoThin film solar cell with 84 power conversion effi-ciency using an earth-abundant Cu

2ZnSnS

4absorberrdquo Progress

in Photovoltaics Research and Applications vol 21 no 1 pp 72ndash76 2013

[20] H Katagiri K Jimbo S Yamada et al ldquoEnhanced conversionefficiencies of Cu

2ZnSnS

4-based thin film solar cells by using

preferential etching techniquerdquo Applied Physics Express vol 1no 4 2008

[21] S Ahmed K B Reuter O Gunawan L Guo L T Romankiwand H Deligianni ldquoA high efficiency electrodepositedCu2ZnSnS

4solar cellrdquo Advanced Energy Materials vol 2 no 2

pp 253ndash259 2012[22] K Maeda K Tanaka Y Fukui and H Uchiki ldquoInfluence of

H2S concentration on the properties of Cu

2ZnSnS

4thin films

and solar cells prepared by solndashgel sulfurizationrdquo Solar EnergyMaterials and Solar Cells vol 95 no 10 pp 2855ndash2860 2011

[23] A V Moholkar S S Shinde A R Babar et al ldquoSynthesis andcharacterization of Cu

2ZnSnS

4thin films grown by PLD solar

cellsrdquo Journal of Alloys and Compounds vol 509 no 27 pp7439ndash7446 2011

[24] J Burschka N Pellet S-JMoon et al ldquoSequential deposition asa route to high-performance perovskite-sensitized solar cellsrdquoNature vol 499 no 7458 pp 316ndash319 2013

[25] H Zhou Q Chen G Li et al ldquoInterface engineering of highlyefficient perovskite solar cellsrdquo Science vol 345 no 6196 pp542ndash546 2014

[26] P Qin S Tanaka S Ito et al ldquoInorganic hole conductor-based lead halide perovskite solar cells with 124 conversionefficiencyrdquo Nature Communications vol 5 article 3834 2014

[27] S Chavhan O Miguel H-J Grande et al ldquoOrgano-metalhalide perovskite-based solar cells with CuSCN as the inorganichole selective contactrdquo Journal of Materials Chemistry A vol 2no 32 pp 12754ndash12760 2014

[28] ZWu S Bai J Xiang et al ldquoEfficient planar heterojunction per-ovskite solar cells employing graphene oxide as hole conductorrdquoNanoscale vol 6 no 18 pp 10505ndash10510 2014

[29] J H Heo S H Im J H Noh et al ldquoEfficient inorganic-organic hybrid heterojunction solar cells containing perovskitecompound and polymeric hole conductorsrdquo Nature Photonicsvol 7 no 6 pp 486ndash491 2013

[30] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 46)rdquo Progress inPhotovoltaics Research and Applications vol 23 no 7 pp 805ndash812 2015

[31] M Hosoya H Oooka H Nakao et al ldquoOrganic thin film pho-tovoltaic modulesrdquo in Proceedings of the 93rd Annual Meeting ofthe Chemical Society of Japan pp 21ndash37 2013

[32] J Yan Q Wang T Wei and Z Fan ldquoRecent advances in designand fabrication of electrochemical supercapacitors with highenergy densitiesrdquo Advanced Energy Materials vol 4 no 4Article ID 1300816 2014

[33] S Tajima T Itoh H Hazama K Ohishi and R AsahildquoImprovement of the open-circuit voltage of Cu

2ZnSnS

4cells

using a two-layered processrdquo in Proceedings of the IEEE 40thPhotovoltaic Specialist Conference (PVSC rsquo14) pp 431ndash434Denver Colo USA June 2014

[34] W S Yang J H Noh N J Jeon et al ldquoHigh-performance pho-tovoltaic perovskite layers fabricated through intramolecularexchangerdquo Science vol 348 no 6240 pp 1234ndash1237 2015

[35] httpwwwnimsgojpengnewspress201506201506170html

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 12: Review Article Emerging Photovoltaics: Organic, Copper ...

12 Journal of Applied Chemistry

[36] N Kaur M Singh D Pathak T Wagner and J M NunzildquoOrganic materials for photovoltaic applications review andmechanismrdquo Synthetic Metals vol 190 pp 20ndash26 2014

[37] J Xue S Uchida B P Rand and S R Forrest ldquo42 efficientorganic photovoltaic cells with low series resistancesrdquo AppliedPhysics Letters vol 84 no 16 pp 3013ndash3015 2004

[38] J G Xue S Uchida B P Rand and S R Forrest ldquoAsymmetrictandem organic photovoltaic cells with hybrid planar-mixedmolecular heterojunctionsrdquo Applied Physics Letters vol 85 no23 pp 5757ndash5759 2004

[39] T Ameri P Khoram J Min and C J Brabec ldquoOrganic ternarysolar cells a reviewrdquo Advanced Materials vol 25 no 31 pp4245ndash4266 2013

[40] J-M Nunzi ldquoOrganic photovoltaic materials and devicesrdquoComptes Rendus Physique vol 3 no 4 pp 523ndash542 2002

[41] K L Mutolo E I Mayo B P Rand S R Forrest and M EThompson ldquoEnhanced open-circuit voltage in subphthalocya-nineC

60organic photovoltaic cellsrdquo Journal of the American

Chemical Society vol 128 no 25 pp 8108ndash8109 2006[42] Y Li and Y Zou ldquoConjugated polymer photovoltaic materials

with broad absorption band and high charge carrier mobilityrdquoAdvanced Materials vol 20 no 15 pp 2952ndash2958 2008

[43] J Hou M-H Park S Zhang et al ldquoBandgap and molecularenergy level control of conjugated polymer photovoltaic mate-rials based onbenzo[l2-b45-b1015840]dithiophenerdquoMacromoleculesvol 41 no 16 pp 6012ndash6018 2008

[44] M Zhang X Guo Z-G Zhang and Y Li ldquoD-A copolymersbased on dithienosilole and phthalimide for photovoltaic mate-rialsrdquo Polymer vol 52 no 24 pp 5464ndash5470 2011

[45] J-F Nierengarten T Gu G Hadziioannou D Tsamourasand V Krasnikov ldquoA new iterative approach for the synthesisof oligo(phenyleneethynediyl) derivatives and its applicationfor the preparation of fullerene-oligo(phenyleneethynediyl)conjugates as active photovoltaic materialsrdquo Helvetica ChimicaActa vol 87 no 11 pp 2948ndash2966 2004

[46] M Edoff ldquoThin film solar cells research in an industrialperspectiverdquo AMBIO vol 41 no 2 pp 112ndash118 2012

[47] M Jiang and X Yan ldquoCu2ZnSnS

4thin film solar cells present

status and future prospectsrdquo in Solar CellsmdashResearch andApplication Perspectives A Morales-Acevedo Ed chapter 5InTech Rijeka Croatia 2013

[48] G Altamura ldquoDevelopment of CZTSSe thin films based solarcellsrdquo Material Chemistry Universite Joseph-Fourier-GrenobleI 2014

[49] P Zawadzki L L Baranowski H Peng et al ldquoEvaluationof photovoltaic materials within the Cu-Sn-S familyrdquo AppliedPhysics Letters vol 103 no 25 Article ID 253902 2013

[50] I Grinberg D Vincent West M Torres et al ldquoPerovskiteoxides for visible-light-absorbing ferroelectric and photovoltaicmaterialsrdquo Nature vol 503 no 7477 pp 509ndash512 2013

[51] J Bisquert ldquoThe swift surge of perovskite photovoltaicsrdquo TheJournal of Physical Chemistry Letters vol 4 no 15 pp 2597ndash2598 2013

[52] A Kojima K Teshima Y Shirai and TMiyasaka ldquoOrganomet-al halide perovskites as visible-light sensitizers for photovoltaiccellsrdquo Journal of the American Chemical Society vol 131 no 17pp 6050ndash6051 2009

[53] T Salim S Sun Y Abe A Krishna A C Grimsdale and Y MLam ldquoPerovskite-based solar cells impact of morphology anddevice architecture on device performancerdquo Journal ofMaterialsChemistry A vol 3 no 17 pp 8943ndash8969 2015

[54] M A Green A Ho-Baillie and H J Snaith ldquoThe emergence ofperovskite solar cellsrdquo Nature Photonics vol 8 no 7 pp 506ndash514 2014

[55] M I El-Henawey R S Gebhardt M M El-Tonsy and SChaudhary ldquoOrganic solvent vapor treatment of lead iodidelayers in the two-step sequential deposition of CH

3NH3PbI3-

based perovskite solar cellsrdquo Journal of Materials Chemistry Avol 4 no 5 pp 1947ndash1952 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Page 13: Review Article Emerging Photovoltaics: Organic, Copper ...

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of