06 Organic Photovoltaics RD India v Kumar

7/29/2019 06 Organic Photovoltaics RD India v Kumar

1/101

Photovoltaics Research inIndia

Vikram Kumar

Ph sics / CARE / NRFIndian Institute of Technology Delhi

[email protected]


2/101

Photovoltaic Devices

Direct conversion of Sunlight into Electricity

Conventional Silicon Solar cells Limitations

Hi h Cost

Commercial Efficiency ~ 16 %

~

Large Area Limitation

Less Flexibility

Thin Film Solar Cells

a Si , CdTe, CIGS and thin film crystalline Si

Commercial Efficiency ~ 10 % Efficiency at Laboratory scale ~ 16 %

Search for cost Organic Solar cells

effectivealternatives

Nanocomposite/organic Solar


3/101

Why Organic Photovoltaics

Solar energy demand has grown ata rate of ~30% p.a. over the last

9Production facilities are >10xcheaper than those for anytraditional PV technolo

The global market for PVinstallations estimated at 18 b

9 Low unit costs enable use

even for shorter lifecycles

Currently the market is heavilydependent on government

9 New form factors(semitransparent foil) allow

subsd es

Lifetime

3flexibility, weight, large area, low cost, tailored properties

os sc ency


4/101

Current in Organic Semiconductors

Need to understand OS is sandwiched between

contacts with different work

Carrier Generation

Trans ort

functions (eg. Al and ITO) giving

rise to an electric field

RecombinationCurrent holes electrons

PPV forms ohmic contact with

ITO, Au for holes.

Ca, Al for electrons

Electron onl and hole onldevices depending on theinjecting contact

4


5/101

Or anic solar cells

Small molecules(vacuum evaporation)

(spin process)

Conjugated Polymers


6/101

in India

~, .

Jawaharlal Nehru Center for Advanced Scientific

Research Ban alore ~2.0%

Indian Institute of Technology, Kanpur (~1.8%)

Indian Institute of Technology, Delhi

, ,

Jawaharlal Nehru University, Delhi


7/101

Hole Acceptors

PPV, MEH-PPV, MDMO-PPV, P3HT, etc

Electron Acceptors (high electron affinities)

- , , , , - -

butyric acid methyl ester (PCBM), perylenes

s mos w e y use

n

O

O

O

O

n


8/101

OPV Working principle


9/101

Earl work with bila er cells

Initially two layer solar cells were made

C. W. Tang , APL 48,183, 1986

CuPC/Perylrene dye cell with

N. S. Sariciftci et al., APL 62, 585 (1993)

~1%

Interface between the organic

la ers is crucial rather than the

Rectification ratio in the dark 104

Short circuit current linear up to 1W/cm2

electrode/organic contact

10-1 %

9


10/101

Distributed Hetero unction Mix electron acceptor and hole acceptor materials together

Distribute active interfaces throu hout the bulk

All excitons are within a diffusion range of an interface

Exciton dissociation at the PPV/C60 interface Electrons transferred to one component, holes to the other

Charges travel to respective electrodes

10-3

-

illuminated

nt

(A/cm

2)

10-7

Curr

10-9

10-1

dark

090202 10

- -Bias (V)

G. Yu and A. J. Heeger: J. Appl. Phys. 78, 4510-5 (1995)


11/101

-1)-1

)

ien

t(c GaAs

(Inorganic)ient(c CuPC

(organic)

Coeffi

nCoeffi

Narrow Band

sorptio

sorptio

Narrow Band

Ab

Energy (eV)Energy (eV)

Energy (eV)

A

+ Can use multiple layers

(tandem solar cells)

Absorbs all photons in solar spectrum

with energy above bandgap energy

The absorption coefficient values are usually higher in organic solar


12/101

h

LUMO level

HOMO level

ec ron exc e

to higher energy level

Absorbed photon creates an exciton

Excitons do NOT always form free electrons and

holes This is especially true in organic semiconductors

,


13/101

Photovoltaic Process In Organic Solar

Cells

Coupling Absorption Creation Separation Collectionhtof sunlight

into

solar cell

of

incident

photons

of

free

charges

of charges

by built-in

E field

of charges

at

electrodes

of

excitonsSunlig

g

Reflected

Away

o ons

Not

Absorbed

Charges

Recombine

'Charges

Recombine

'Excitons

Recombine

'' ' ' 'Efficiency of this step is ~100%for inorganic solar cells


14/101

-

bi

Ef bi

n-typep-type Ebuilt-in

u - n

rgan c a er aInorganic semiconductord

No charge of its own

Built-in potential depends on electrode work function difference


15/101

OSC is typically different from inorganic solar cells in the following ways:

Absor tion in a narrower s ectral band

Usuall hi h absor tion coefficient

Exciton bindin ener hi her

Poor charge mobility

Built-in potential dependent on electrodes


16/101

bi-layer and bulk-heterojunction

(blend) organic solar cells

090202 16


17/101

Optical Absorption in PPV-PCBM

Blends

decreasing from 1-6

Total absor tion is decreasin

PCBM

with the increase in the PCBM

concentration

Still best performance at 80%.

PPV

Jain et al, Syn Met, 148, 245 (2005)


18/101

Bulk heterojunction polymer solar Cells

ITO/PEDOT:PSS/P3HT:PCBM (1:1)/A

0.005

0.010

0.005

0.010

Dark

)

0.0000.000

nsity(A/cm

um na e

-

-0.005

-

-0.005

Current

de

-1.0 -0.5 0.0 0.5 1.0

-0.015

.

-0.015

.

S.No. Voc(V) Jsc(mA/cm2

)

FF(%) (%)

Voltage (V)

090202 18

1. 0.60 8.01 33.2 1.99

Device active area = 11.2 mm2


19/101

Small molecular PV Cells

0.12

ITO/ZnPc:C60/BPhen/Al

0.35

0.40

ZnPc

0.08

0.10

(A/cm

2) Illuminated

ar

0.25

0.30

.

nce

(a.u.)

C60

0.04

.

entdensity

ZnPc

0.10

0.15

0.20

Absorb

-0.02

0.00

.

C

ur

0.05

300 400 500 600 700 800

2

-2 -1 0 1 2

Voltage (V)

. . oc sc 1. 0.50 6.51 51.5 2.09

19



20/101

Dual donors for broad s ectral covera e

ITO/CuPc(20-x nm)/Sub-Pc(x nm)/C60(40 nm)/BPhen(8 nm)/Al

(nm)oc sc

(mA/cm2)

0 0.42 2.68 45.3 0.64

. . . .

2 0.42 5.16 47.8 1.29

3 0.43 2.61 40.0 0.56

. . . .

20 0.60 3.13 25.2 0.59

Device exhibited maximum efficiency ~ 1.3 % forx = 2 nm

20

Kumar et al. J. Phys. D: Appl. Phys. 42, 15103 (2009)


21/101

Bulk heterojunction polymer solar Cells

ITO/PEDOT:PSS/P3HT:PCBM (1:1)/Al

0.005

0.010

0.005

0.010

Dark

)

0.0000.000

nsity(A/cm

um na e

-

-0.005

-

-0.005

Current

de

-1.0 -0.5 0.0 0.5 1.0

-0.015

.

-0.015

.

S.No. Voc(V) Jsc(mA/cm2

)

FF(%) (%)

Voltage (V)

21

1. 0.60 8.01 33.2 1.99



22/101

Effect of illumination and temperature on Voc

0.015

Dark

Bilayer device ITO/CuPc/C60/BPhen/Al

0.005

0.010

sity(A/cm

2) .

OD 0.6

OD 0.4

OD 0.2

OD 0.1

0.000

CurremtDe OD 0.0

0.015

2) 295 K

295 K

-0.005

0.005

.

nsity(A

/c

254 K233 K

213 K

-1.0 -0.5 0.0 0.5 1.0- .

Voltage (V) 0.000

C

urrentd

-0.005

Initial illumination intensity - 80 mW/cm2

-1.0 -0.5 0.0 0.5 1.0

- .

Voltage (V)

ur mo e exp a ns ese

observations as well


23/101

Spectral response characterisation

Spectral ellipsometry

Physics and circuit model of organic solar cells

Choice of material

tructure en , ayer, tan em

Process optimisation

Reliability and stability

Choice of material

Mechanism of degradation

Enca sulation techni ues New & emerging technology issues

Novel methods of fabrication


24/101

Suman Banerjee

Suman Banerjee


25/101

Calcium-Aluminium Cathode

P3HT:PCBM BlendPEDOT:PSS

PEDOT:PSS - 30 nm;

Glass

P3HT:PCBM (1:1) - 90 nm;

Ca - 6 nm; Al - 70 nm.

Characterstics of a typical Organic (Polymer) Solar CellArun Tej Mallajosyula

A i b B i


26/101

Anirban Bagui

P3HT: PCBM Blend Aluminium Cathodee eros ruc ure

PEDOT:PSS

ITOGlass

Vinod Pagare 2007


27/101

-

improves device efficiencyAnirban Bagui Indian Patent being filed


28/101

Modifying Interface by

Annealing

As deposited CuPc Annealed CuPcSmoother

Specially Annealed CuPcSmoother with pillars

C60

Al

ITO

CuPc

between CuPc and C60Area

Glass

Anukul Prasad Parhi Indian Patent being filed


29/101

0.9

1.2P3HT:PCBM:SWNT (0.75 %)

P3HT:PCBM

24FF

570

Voc5.0

Jsc

0.0 0.1 0.2 0.3 0.4 0.50.0

0.3

.

Acm-2) Voltage (V)

21

5604.0

4.5Jsc

Voc

FF(%)

(mV)(mA cm

-2)

-0.6-0.3 =2.99 %

=2.01 %JL(

AM 1.5 G

5553.5

-1.2

- .Intensity =6 mW cm-2

0.0 0.2 0.4 0.6 0.8 1.0

SWNT wt%

5503.0

Incorporation of single walled nanotubes can improve solar cell performance

Main role of nanotube is in charge transport within the solar cell

Aurn Tej Mallajosyula


30/101

Degradation under Electrical & Optical Stress

Statistically arrive at parameters that matter most

Identify the physics of degradation

Munish Jassi 2006


31/101

Tandem small molecular solar cell with

m xe e ero unc ons

Cell B Efficiency 5.70.3 % 100 mW/cm

J. Xue, Appl. Phys. Lett. 85, 5757 (2004).


32/101

Polymer Tandem bulk heterojunction solar cell

Tandem cell Efficiency ~ 6. 5 %.

Kim J Y et al. Science 317, 222 (2007).


33/101


34/101

Hybrid Organic-Inorganic Solar Cells

Polymer: Inorganic Nanocomposites based Solar cells

Cost Effective

Efficient Electron Transport

Strong Optical Absorptionc en exc on ssoc a on

Prepared by Inexpensive Wet Chemical Synthesis

size of the nanoparticles- quantum size effect

Nanoparticlepolymer cells generally have a photoactive

layer consisting of interconnected semiconductingnanoparticles in a solid semiconducting polymer phase i.e.

interpenetrating phases of semiconducting polymers and

nanopar c es


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General rinci les

Con u ated Po ersP3HT, MEH-PPV

Semiconducting Nanoparticles/Quantum dotsCdSe, PbSe, CdTe, CdSexTe1-x, CdS, PbS, ZnO, TiO2

Quantum dots have large surface energies highly unstable high

35

tendency to agglomerate nonhomogeneous dispersion in polymer

matrices hinders charge transport limits efficiency


36/101

CdSe E bulk = 1.7 eV

CdTe ( Eg bulk = 1.49 eV)

PbSe ( Eg bulk = 0.26 eV)

PbS ( Eg bulk = 0.37 eV)

Energy-level positions of MEH-PPV, P3HT, and Semiconductor Nanocrystals (NCs)of different sizes

Unlike PCBM and TiO2, CdSe nanoparticles absorb solar

spectrum edge

ev ces compose o po ymer an s s ow:

good diode characteristics

sizable photovoltaic response in spectral range from

nm

090202 36

the ultraviolet to the infrared

X. Jiang et al., J. Mater. Res., Vol. 22, No. 8, 2007

nm

P l CdS N it S l C ll


37/101

Polymer:CdSe Nanocomposites Solar Cells

. . .,

with lengths 30 nm

Enhanced EQE and power conversion

efficiencies could be realized with the use of

The use of nanorods and tetra ods of CdSe

high aspect ratio CdSe nanorods which provide adirect path for e transport

with P3HT and MEH-PPV, show power

conversion efficiencies of 1.8%

090202 37

e curren -vo age c arac er s cs o nm y nm nanoro ev ce

exhibit rectification ratios of 105 in the dark and short circuit current of0.019 mA/cm2 under illumination of 0.084 mW/cm2 at 515 nm


38/101

Experiment Details for the Synthesis

of CdSe NanoparticlesThe organometallic precursor route involves a coordinating

solvent TOPO Trioctylphosphine Oxide which is hazardous,

unstable, expensive and environmentally unfriendly

Much chea er and safer non-TOP-based route for lar e-scale synthesis of CdSe QDs was proposed by Deng et

al.(2005)

Procedure:

0.0514 of CdO 0.1116 of TDPA and

Chemicals used:

CdO - Cadmium Oxide

-

1.8884 g of TOPO were loaded into a 100

mL flask. The mixture was heated to 300-

TOP - Trioctylphosphine

TDPA - Tetradecylphosphonic Acid

- un er r ow, an was

dissolved in TDPA and TOPO. Solution

was cooled to 270 C; selenium stock

Capping agents used: Trioctylphosphine Oxide (TOPO) Oleic Acid OA

090202 38

solution 1M (0.0205 g of selenium powder

dissolved in 1.2 ml of TOP) was injected.

Cadmium toSelenium ratio:

1:1; 2:1; 3:1


39/101

Colloidal Particles Engineer reactions to precipitate quantum dots from

solutions or a host material (e.g. polymer)

In some cases, need to cap the surface so the dot

remains chemically stable (i.e. bond other molecules onthe surface)

Can form core-shell structures

Typically group II-VI materials (e.g. CdS, CdSe)

Size variations ( size dispersion)

CdSe core with ZnSshell QDs

Blue: smaller dots!

Synthesis approach:


40/101

Synthesis approach:

12 nm (CdO : Se ~ 0.5:1)

7 nm (CdO : Se ~ 1:1)TOP-Se/Ar gasCdO +

9 nm (CdO : Se ~ 3:1)

~

> 300o C

TOPO/OA- capped CdSe

TOPO/OA +

TDPA

Size regulating factor Cd

optimized conditionto Se precursor ratio

Preparation of Polymer:CdSe Nanocomposites

Pyridine solvent:

- Uncapped CdSe particlesToluene solvent:

- appe e par c es

090202 40

Figure shows the Capped and Uncapped CdSe nanoparticles dispersed in

Polymer matrix


41/101

Synthesis of CdSe Quantum Dots

Conclusions

9We have successfully synthesized high quality CdSe

quantum dots

o Nearly-monodispersed

o Highly Crystalline

9 Cd:Se = 2:1 is the optimized condition as for both the capping casessmallest particles were achieved

e :

CdSe(TOPO) 2:1

~ 7 nm

~ 5 nm

9 CdSe(OA) 2:1 particles show better properties compared to CdSe(TOPO) 2:1

- Steric stability

- Photoluminescence

090202 41

- Photostability

Eff t f CdS t d t h l t t


42/101

Effect of CdSe quantum dots on hole transport

n po y - exy t op ene t n ms

ITOPEDOT:PSS

P3HT

Au

Glass substrate

20 nm20 nm

P3HT:CdSe

Au

Glass substrate

ITO:

TEM image of CdSe quantum

dots (size ~ 5 nm) dispersed

in P3HT matrix in 1:1 weightDevice 2ratio

The incorporation of CdSe quantum dots in P3HT results in enhancement in

090202 42

, .,

trap and mobility models to only trap modelKusum et al, Appl. Phys. Lett., 92, 263504 (2008)

D st ti f S l C ll


43/101

Demonstration of Solar Cell.....

P3HT: PCBM ITO/ PEDOT:PSS/ P3HT:PCBM/ LiF/ Al

P3HT: CdSe: PCBM ITO/ PEDOT:PSS/ P3HT:CdSe:PCBM/ LiF/ Al

Jsc = 6.32 x 10-3A/cm2

Voc = 0.44 V

Jsc = 8.88 x 10-3A/cm2

Voc = 0.48 V0.0

5.0x10-3

J(A/cm

2)

FF = 0.435 FF = 0.36

-0.25 0.00 0.25 0.50 0.75

-5.0x10-3

V (Volts)

= 1.23 % = 1.91 %

-1.0x10-2

P3HT: PCBM

P3HT: CdSe: PCBM

-1.5x10-2

090202 439 Reduction of barrier at active layer- acceptor interface

Demonstration of Solar Cell


44/101

Demonstration of Solar Cell.....

MEH-PPV:PCBM ITO/ PEDOT:PSS/ MEHPPV:PCBM/ LiF/ Al

-PPV:CdSe:PCBM

ITO/ PEDOT:PSS/ MEHPPV:CdSe:PCBM/ LiF/ Al

-2

Jsc = 2.88 x 10-3A/cm2

Voc = 0.37 V

Jsc = 7.37 x 10-3A/cm2

Voc = 0.41 V5.00x10-37.50x10

-3

.MEH-PPV: PCBMMEH-PPV: CdSe: PCBM

/cm

2)

FF = 0.46

=

FF = 0.40

=-0.25 0.00 0.25 0.50

-2.50x10-3

0.00

2.50x10-3

J

(A

. .

-7.50x10-3

-5.00x10-3

B

A

-1.00x10-2

CdSe QDs have a range of electron affinities reported from 3.5-4.5 eV help

090202 44

PCBM provides additional conducting path allowing significantenhancement of electron transport at even low doping levels

P l

Nanoparticles Voc

(V)

Jsc

( A/ 2)

EQE PCE

(%) R f


45/101

Polymer (V) (mA/cm2) (%) References

OC1C10-PPV CdSe tetrapods 0.75 9.1 0.52 2.8 B. Sun et al., J Appl Phys

97 (2005) 014914

P3HT CdSe nanorods 0.62 8.79 0.70 2.6 B. Sun et al., Phys Chem Chem Phys 8(2006) 3557

APFO-3 CdSe nanorods 0.95 7.23 0.44 2.4 P. Wang et al., Nano Lett 6 (2006) 1789

. . . . .,

7 (2007) 40914

P3HT CdSe nanorods 0.70 6.07 0.56 1.7 W. U. Huynh et al., Science 295 (2002)24257

MDMO-PPV ZnO 0.81 2.40 0.39 1.6 WJE Beek et al., Adv Mater 16 (2004)

100913MEH-PPV CdSe tetrapods 0.69 2.86 0.46 1.13 Zhou Y, Nanotechnology

17 (2006) 40417

MDMO-PPV ZnO 1.14 2.30 0.26 1.1 WJE Beek et al., Adv Funct Mater 15(2005) 17037

MEH-PPV CdSexTe1x 0.69 1.57 0.49 Yi Zhou et. al., Nanotechnology 17

0.78 0.22

MEH-PPV CdTe

nanocrystals

0.77 0.19 0.42 T. Shiga et al., Solar Energy Materials& Solar Cells 90 (2006) 18491858

090202 45

. . . . . .,

D: Appl Phys 38 (2005) 200612

P3HT PbSe 0.35 1.08 0.14 D Cui et al., Appl Phys Lett88 (2006) 183111


46/101

The Potential of


47/101

The Potential of

www.konarka.com

Konarkas solar bags

A potential cottage industry

www.crunchwear.com/solar-powered-fashion-accessories/

Production is distributed

www.scienceknowledge.org

S mmar and Concl sions


48/101

Summar and Conclusions

We have reviewed the status ofnove so ar ce s

Nanoparticles are used in

improve the solar energy

New materials are the key toro ress to im rove absor tion

for longer wavelenghts

There are several groupswor ng on ese aspec s nIndia.


49/101

I thank numerous persons who have

contributed to this resentation

First generation PV


50/101

First generation PV

Second Gen PV


51/101

Second Gen PV

3rd Gen PV


52/101

3 Gen PV

4th Gen


53/101

4 Gen


54/101

-1)-1

)

ie

nt(c GaAs

(Inorganic)ient(c CuPC

(organic)

Coeffi

nCoeffi

Narrow Band

sorpt

io

sorp

tio Narrow Band

Ab

Energy (eV)Energy (eV)

Energy (eV)

A

+ Can use multiple layers

(tandem solar cells)

Absorbs all photons in solar spectrum

with energy above bandgap energy

The absorption coefficient values are usually higher in organic solar


55/101

hLUMO level

HOMO level

ec ron exc e

to higher energy level

Absorbed photon creates an exciton

Excitons do NOT always form free electrons and

holes This is especially true in organic semiconductors

,



56/101


Cells

Coupling Absorption Creation Separation Collectionht

of sunlight

into

solar cell

of

incident

photons

of

free

charges

of charges

by built-in

E field

of charges

at

electrodes

of

excitonsSunlig

g

Reflected

Away

o ons

Not

Absorbed

Charges

Recombine

'Charges

Recombine

'Excitons

Recombine

'' ' ' 'Efficiency of this step is ~100%

for inorganic solar cells


57/101

-bi

Ef bin-typep-type

Ebuilt-in

u - n

rgan c a er aInorganic semiconductord

No charge of its own

Built-in potential depends on electrode work function difference


58/101

OSC is typically different from inorganic solar cells in the following ways:

Absor tion in a narrower s ectral band

Usuall hi h absor tion coefficient

Exciton bindin ener hi her

Poor charge mobility

Built-in potential dependent on electrodes


59/101

At IIT Kanpur


60/101

http://www.iitk.ac.in/scdt/


61/101

Dr. Deepak Gupta

Dr. Y.N.Mohapatra

Dr. Dr. B.Mazhari

Engineers

Dr. J. Narain .

Dr. Satyendra Kumar

Dr. S.S.K.Iyer

Dr. Ashish Garg

Dr. Vandana Singh

Dr. Ashish Gupta

.

Visiting ResearchEngineers

Dr. Unni Narain

Dr. Asha Awasthi

Mr. I. V. Kameshwar Rao

Support Staff

Mr. Dharmendra Swain

Mr. Arvind Kumar Students r. an r ng Mr. Boby C. Villari

Mr. Pankaj Uttwani

Dr. Ganesan Palaniswami

Mr. Ramnath Yadav

Mr. Dinesh Kumar

Mr. Ajay Naik

Ms. Mamata Rai

Ph.D : 19

M.Tech : 22

Ms. Shewta Maurya. . .


62/101

Dis la

Metal Lines

COF

Images Captures on the displayDisplay Module,

made at SCDT

, ,

Passive Matrix, consisting of the

OLED Display, COF and Driver.


63/101

Pushing the Envelope of

Understanding of Organic Devices

Dis la s

Lighting

Solar Cells

CoreExpertise &

OLED

Sensors

The new age of Macro-electronics

Printable, Flexible, Large, Cost Effective !


64/101

-

WOLED

O-TFT (printable)

O-Solar Cells

OLED Displays

Getting

Started

Exploratory

StagePrototyping

with

Industrial Partner


65/101

On-going work at IIT Kanpur


66/101

Discrete Devices Module ApplicationsOrganic Molecules


67/101

Vacuum Thermal DepositionWet Processing

R = Hexyl group

C60CuPcPCBMP3HT

In-house

biodegradable

molecules

- -

Modified Chromophor of GreenFluorescent Protein Prof. R. Gurunath Modified Porphyrin moleculesProf. S.P. Rath


68/101

Spectral response characterisation

Spectral ellipsometry

Physics and circuit model of organic solar cells

Choice of material

tructure en , ayer, tan em

Process optimisation Reliability and stability

Choice of material

Mechanism of degradation

Enca sulation techni ues

New & emerging technology issues

Novel methods of fabrication

Suman Banerjee


69/101

Suman Banerjee


70/101

Calcium-Aluminium Cathode

P3HT:PCBM Blend

PEDOT:PSS

PEDOT:PSS - 30 nm;

Glass

P3HT:PCBM (1:1) - 90 nm;

Ca - 6 nm; Al - 70 nm.

Characterstics of a typical Organic (Polymer) Solar Cell

Arun Tej Mallajosyula

Anirban Bagui


71/101

P3HT: PCBM Blend

Aluminium Cathode

e eros ruc ure PEDOT:PSS

ITOGlass

Vinod Pagare 2007

-


72/101

improves device efficiency

Anirban Bagui Indian Patent being filed

Modifying Interface by


73/101

Annealing

As deposited CuPc Annealed CuPcSmoother Specially Annealed CuPcSmoother with pillars

C60

Al

ITO

CuPc between CuPc and C60Area

Glass

Anukul Prasad Parhi Indian Patent being filed


74/101

0.9

1.2P3HT:PCBM:SWNT (0.75 %)

P3HT:PCBM

24FF

570

Voc5.0

Jsc

0.0 0.1 0.2 0.3 0.4 0.50.0

0.3

.

Acm-2) Voltage (V)

21

5604.0

4.5Jsc

Voc

FF(%)

(mV)(mA cm

-2)

-0.6

-0.3

=2.99 % =2.01 %

J

L(

AM 1.5 G

5553.5

-1.2

- .Intensity =6 mW cm-2

0.0 0.2 0.4 0.6 0.8 1.0

SWNT wt%

5503.0

Incorporation of single walled nanotubes can improve solar cell performance

Main role of nanotube is in charge transport within the solar cell

Aurn Tej Mallajosyula


75/101

Degradation under Electrical & Optical Stress

Statistically arrive at parameters that matter most Identify the physics of degradation

Munish Jassi 2006

Plasmonics


76/101

Bulk Metal

DecreasingUnoccu ie

the sized states

occu ied

5 nm

Close l in

states

Separation between

bands

conduction bands

motion that is not confined confined, and quantization sets in

Particle size < mean free ath

of electrons

Unusual Properties on the nm ScaleUnusual Properties on the nm Scale are realizedare realized


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in centuries backin centuries back

particles about 10 nm in

diameter, it looks wine-red

-

ruby-red stained

glass from gold,how close the particles are

together

nanoparticles

Surface Plasmon Absorption of Au

520 nm


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0.3

520 nm

0.2

s

o

r

tio

n

0

0.1A

b

Au colloids Size ~7-8 nm

300 400 500 600 700 800

Wavelength (nm)Optical response of a nanoparticle depends on its size, shape,

Surface plasmon absorption is due to coherent motion of conduction band electrons

co ec ve e av our an oca e ec r c env ronmen

after incident EM radiation

++ + +++

-- - - -- - -

Metal Nanoparticles --

Localized surface lasmons


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Collective motion of electrons is called plasma ,

Ag, Al

7-8 nm

Rough surface Grating structure

NanoparticlesBulk Gold

+ +++ + ++

+

-- - - -- - -

Metal nanoparticles Conduction electrons acts like oscillator

Plasmonics for photovoltaics

,


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typically achieved using a pyramidal surfacetexture that causes scattering of light into the

,

increasing the effective path length in the cell.

Such large-scale geometries are not suitable for thin-film cells, for

thickness) and because the greater surface area increases minority carrier

recombination in the surface and junction regions.

-

of metallic nanostructures that support surface plasmons:

o excitations of the conduction electrons at the interface between a

.

o By proper engineering of these metallodielectric structures, light

can be concentrated and folded into a thin semiconductor layer,

.o Both localized surface plasmons excited in metal nanoparticles

and surface plasmon polaritons (SPPs) propagating at the

Plasmonic light-trapping geometries for thin-film

solar cells


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at the surface of the solar cell. Light is preferentiallyscattered and trapped into the semiconductor thin film

- ,

increase in the effective optical path length in the cell.

(b) Light trapping by the excitation of localized surface

plasmons in metal nanoparticles embedded in the

semiconductor. The excited particles near-field

causes the creation of electronhole pairs in thesemiconductor.

plasmon polaritons at the metal/semiconductor

interface. A corrugated metal back surface couples

li ht to surface lasmon olariton or hotonic modes

that propagate in the plane of the semiconductor

layer. Nature materials VOL 9, 2010,205

Surface plasmon enhanced Si


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solar cell

a. Enhancement from a double-

s e po s e wa er characterized optically using a

sizes formed from differentmass thickness of silver by

thermal evaporation followed by

annealing.

. o a an use re ec anceplots from a double-sided

oxidePillai et al JAP,101, 093105 2007

Phos hors


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Photon accounting of a Si solar cells shows about.

contributing to the output energy due to the

thermalization of the excited electrons/holes to the

respective band edges.

The photons with energy below the band gap are not

absorbed in the base region and are mostly lost.

These two optical losses

combine to result in ~ 50% of

contributing to the

hotovoltaic conversion


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The second loss mechanism is imperfect collection due.

Since high energy photons are absorbed in this regionthey are more likely to be affected and the result is areduced spectral response at shorter wavelengths.

This loss can be reduced by using phosphors that,

the higher spectral response region (500 -1000 nm) ofthe Solar cell.


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e r oss mec an sm s ransm ss on, w coccurs because photons with energy less than the

band a of silicon are not absorbed. Transmission losses can be reduced by employing

up-conversion (UC) processes, whereby two or moreow energy p o ons com ne o crea e one g er

energy photon.

solution for enhancing the cell efficiency butunfortunately, no breakthrough has been reported

ye n s area. s ma es e ssue more arge -oriented and challenging to pursue research forsuitable hos hor/nano hos hor coatin s for improvements in the efficiency of solar cell.


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Thermalization.

Wavelen th < 2E of Si

Down Conversion/ Photoluminescence

Phosphors

Transmission.

Wavelength > Eg of Si

Up Conversion Phosphors

N P LI N D I A

Up-Conversion (UC) Phosphor: Absorbs IR and emits in VIS-NIR

Down Conversion (DC) Phosphor: Absorbs UV-VIS and emits in VIS-NIR


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The Phosphor Layer should be transparent to wavelengths other than its absorption.

N P LI N D I A IIT, Delhi

SolarSpectrumModificationUsingNovelNanoandBulkPhosphorsforEnergy

EfficientSolarCells

A romisin conce t for efficient harvestin of solar ener usin solar cells is

Spectrum Modification using phosphors


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P otograp s o YV 4:Eu+

colloidal solution and red

emission from spin coated

a es ow ng~t ree

timesincrementinIsc at


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of solar power by using inexpensive

su s ra es an a ower quan y anquality of semiconductor material.

However, the resulting short optical path

len th and minorit carrier diffusion

length necessitates either a high

trapping.

Silicon Nanowires

Light absorption Longitudinal direction


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Light absorption Longitudinal direction

arr er co ec on ransverse rec on

Excellent L ight trapping structures

Improved material properties due to miniaturization

Offers new eometries for solar cells - not ossible with bulk or thin films

A SiNWs based solar cell (with radial p-n junctions):SiNWsbased solar cells aremuch less sensitiveto theimpurities ascompared with planar p-n junction solar cells

Theoretically(JAP 97, 114302

(2005))

mg-Si can be usedinstead of s -Si

~half of the total energy required to fabricate a solar

Direct impact on: Processing cost & Energy payback time

FabricationofNanowires

Gas PhaseSynthesis (BottomupApproach)


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Gas-Phase Synthesis (Bottom up Approach) - -

(both by CVD and PVD methods)

- PECVD, MBE etc.Oxide Assisted Growth (OAG)

Etching Methods (Top down Approach)

Metal catalyzed wet Chemical etching/Template-Based Synthesis

Dry Etching such as reactive ion etching (RIE) etc.

SINGLE-NANOWIRE SI SOLAR CELLS

H. A. Atwater Group

California Institute of Technology, Pasadena, CA 91125


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Coaxial silicon nanowires as solar cells

Charles M. Lieber Group


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NATURE| Vol 449| 18 October 2007, 885-890

Chem. Soc. Rev., 2009, 38, 16 - 24, DOI: 10.1039/b718703n


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NATURE| Vol 449| 18 October 2007, 885-890

Axial p-n Junctions Realized in Silicon Nanowires by

Ion Im lantation

S. Hoffmann, J. Bauer, C. Ronning, Th. Stelzner,| J. Michler, C. Ballif, V. Sivakov,,| and S. H.

Christiansen*,,|


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Nano Lett., Vol. 9, No. 4, 2009

Light Trapping in Silicon Nanowire Solar CellsPeidong Yang Group at University of California, Berkeley, California


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DOI: 10.1021/nl100161z | Nano Lett. XXXX, xxx, 000-000

Silicon Nanowire Radial or coaxial p-n Junction Solar CellsPeidong Yang Group at UniVersity of California, Berkeley, California and Lawrence Berkeley National Laboratory, Berkeley,

a orn a


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Efficiency and other cell

J. AM. CHEM. SOC. 2008, 130, 92249225

Silicon Nanowire-Based Solar Cells on GlassS. H. Christiansen Group, IPHT, Jena, Germany


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Efficiency and other cell

parameters and limitations

Nano Lett., Vol. 9, No. 4, 2009, 1549-1554

Developed a novel room temperature process for large area

Silicon Nanowires array: Growth & Optical PropertiesSingle crystalline SiNWs

growth of SiNW arrays via selective wet chemical etching

of silicon (Top Down approach)


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( p pp )

20

25

30

35

ength(m)

u

(400)

(220)(2-20)0 20 40 60 80 100 120

0

5

10

15

SiNW

arraysl

5 m

SiNW arrays have very low surface reflectivity (~2 % ) and therefore, potential

J . Nanoparticle Research 2010(in Press)Etching time (min)

9Aligned, Dense, Controlled arrays length, =100-300nm

application in solar cells

50

60

SiNW arrays Polished Si

10

20

30Polished

2min

90s

60s

R(%

)

9Low R


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(a) (b)

a. Control solar Cell: CMP wafer

b. SiNW arrays based black cells

0.8

1.0

Efficie

ncy

40

50

(%)

(b)

-10

0

A/cm2

)Control cell

Cell with selective SiNW arrays of 4 m length

(a)

0.4

0.6

control cell

selective SiNW arrays cell (~4m)cell based on entire area SiNW arraysn

alQuantum

20

30

Reflectivity

-20

ntDensity(m

400 500 600 700 800 900 1000 11000.0

0.2

control cell

SiNW arrays cell (~4m)Inte

0

10

0 100 200 300 400 500 600

-40

-30

Curr

19th PVSEC, 9-13 Nov, 2009, J eju,, Korea

Proc.34th IEEE PVSC, 2009, pp. 1851-1856

Solar Energy Mater & Solar cells 2010 (In Press)

Voc(mV)

9 ~20 % enhancement in Jsc and ~1% absolute

in conversion efficiency in SiNW based cells

06 Organic Photovoltaics RD India v Kumar

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