Current Status of Solar Photovoltaic Technology …...2009/12/27 · Photonic Spectra Webinar “PV...

Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #1

Current Status of Solar Photovoltaic Technology Platforms, Manufacturing

Issues and ResearchSteve Hegedus

Institute of Energy ConversionUniversity of Delaware

With assistance from IEC staff: Brian McCandless (CdTe), Bill Shafarman (CIGS)


Outline Introduction to IEC at U of Delaware

PV trends, growth in scale, contribution to energy production

Crystalline Si PV status, baseline technology, near term focus: New methods emitter formation, passivation and device

architecture

Thin Film PV status, baseline technology and near term focus: Cu(InGa)Se2 : wide gap alloys, improved 2-step selenization CdTe: higher deposition T , substrate a-Si/nc-Si (briefly) : multijunction, collapse of the a-Si industry

Two common PV myths


Institute of Energy Conversion at U of Delaware Founded in 1972 to perform thin-film PV research

World’s oldest continuously operating

solar research facility

First 10% efficient thin film solar cell (1980)

Dept of Energy University Center of Excellence

for Photovoltaic Research and Education (1992)

Soft funded - government and industry contracts

2012 staff: 11 professional, 3 tech, 2 admin, 5 post doc, >20 grad students (4 depts)

Recently rec’d $8.4M from DOE (3 year grants)

First flexible10% cell

4x4 inchminimodule


IEC Research Program Goals Expand the fundamental science and engineering base for

thin film and c-Si photovoltaics to improve performance

Transfer these technologies to large-scale manufacturing IEC has been responsible for growth of several PV start-ups

through technology transfer and validation

Provide workforce with PV scientists and engineers

>40 graduates since 1992 (PV Center of Excellence)


IEC Technology Thrust Areas Thin film polycrystalline CuInGaSe2-based (CIGS) solar cells

Thin film polycrystalline CdTe solar cells

Silicon-based solar cells

Front and back contact heterojunction (a-Si/c-Si)

Thin film tandem a-Si and nc-Si


IEC Facilities: complete capability for fabrication and characterization of thin film and c-Si solar cells

Over 20 thin-film deposition systems: PECVD (vhf/rf/dc), HWCVD, PVD, Vapor Transport, sputtering, H2S/H2Se reaction, chemical bath

Materials characterization: XRD, GIXRD, VASE, EDS, SEM, AFM, AAS, XPS, FTIR, Raman, optical trans+refl, Hall effect

Device fabrication: complete capability for high efficiency solar cells:

c-Si (front heterojunction and IBC), CdTe, Cu(InGa)Se2 , a-Si

Laser and mechanical scribing for monolithic module fabrication

Device characterization: J-V, J-V-T, QE, C-V, OBIC, accelerated life stress (damp-heat, ambient, light)


The Big Picture: PV applications and achievements


PV can be installed anywhere, 10’s Watts to 100’s Megawatts


Recent worldwide achievements Installation: 17 GW in 2010 (100% growth), 30 GW in 2011 (70% growth)

Average annual growth >50% p/y for decade

EU: PV providing 2-4% of annual electricity in Spain, Germany, Italy May 2012 Germany received >10% from PV On one day >40% (22 Gigawatts peak supply out of 27 GW installed)

US: 5.7 GW installed, 2 GW in CA Over 70% of 2011 installations are ‘utility scale’ or > 100 kW Worlds largest PV power plant 250 MW Aqua Caliente Project (CA, thin film)

Creating hundreds of thousands of jobs 400,000 in Germany; 100,000 in US R&D, manufacturing, supply chain (materials), system design, installation


Trend in PV applications: 1990-2009 1995: PV demand driven by off-grid applications

After 1995: Innovative policy in Japan, Germany stimulated market for grid-connected residential and commercial

>2008: Asian Si modules drove down prices, increased installations

>2010: Significant growth in utility scale > 1 MW projects

2012: First year of flat or negative growth in decades,

projected to recover 2013


Industry in turmoil: ‘roller coaster ride’ Significant consolidation, bankruptcy, closures in past 2 years

Top companies for years suddenly quit PV or bankrupt

Worldwide capacity ~ twice demand yet demand still growing

Huge excess inventory

Shrinking profits - many companies selling at loss to compete

c-Si done much better in price and efficiency than many expected, squeezing thin film start ups

Renewed emphasis on improving performance since costs so low


Brief Overview of PV Basics


What is a PV device?Direct converter of light into electricity:photons in, electrical current (DC) out

Three critical processes:Light Absorption + Carrier Generation + Carrier Collection

(current flow) (deliver P to load)

e -h+

e -

h+

load

charge separation

V+

V-


Cell efficiencies vs. bandgap EG Record performance single junction cells vs. theoretical limit

Expect maximum performancewith EG ≈ 1.5 eV

But theor eff >25% possible EG ≈ 1 – 1.8 eV

Many thin film, III-V options a-Si/nc-Si 2J


Commercial Scale PV Devices Single crystal or multicrystalline Si wafers

Dominate market: 85-90% of sales Solar grade Si, lower qual than IC Module efficiency: 14-20% Low cost Asian Si driving prices down

Thin films (1-3 µm polycrystalline or amor) Ultimately lower cost than Silicon wafers (??) On glass, metal or plastic foils Diverse materials, techniques Lower quality, imperfect crystallization, more defects Module efficiency: 8-14% Unique advantages in building integrated products 10-15% of market, #2 PV company is TF CdTe (First Solar)


One common PV challenge: reducing gap between champion cell and module efficiency

Wolden et al, JVST-A 29 (2011) 030801

Multi c-Siand TF CIGSboth ~20%cell efficiency.But mc-Si has more mature module technology.


Why efficiency matters – fixed BOS costs

Wang et al Renewable and Sustainable Energy Rev (2011)

Levelized cost of Energy:• Lifecycle costs/energy • LCOE costs include Balance of System whichscale with # modules, area• Lower eff = higher BOS$• More rack, wiring, install $• y-intercept is system price without module• Si modules ‘selling’ at $0.9/WOr $120/m2


Crystalline Si (c-Si) Technology and Advanced Concepts


Standard commercial Si PV cell processstart

finish

900°C

400°C

900°C


Commercial Si Solar Cell, Eff ~ 15-17%

Front contact (Screen printed Ag fired through SiN)

(~ 0.3 µm)

RandomtexturedF and R


World record Si solar cell: PERL

Cell Voc (V) Isc (mA/cm2) FF(%) Eff(%)PERL 0.70 42 81 24.7

• PERL cell: Passivated Emitter, Rear contact Locally diffused• 2-step emitter (thin n between contact and thick n+ under contact)• UNSW, AU, 1998; very complex design, not manufacturable


Conflicting emitter properties: pn junction vs resistance vs absorbing ‘dead layer’

property Advantage DisadvantageIncrease thickness •Reduce lateral R for

current flow to Ag contact•Prevent melting Ag SP metal penetrate to base

•Increase absorption in highly defect layer (photons not converted to e-h pair), lower blue QE and Jsc

Increase doping •Reduce lateral R•Reduce contact R with Ag or other metal grid

•Increase defects and recombination (Io) so decrease Voc

Increase bandgap •Decrease absorp loss•Increase band bending, reduce recomb (Io)

•Increase lateral resistance significantly, req second conductive layer ($$)


Why not ‘tune’ the emitter to have properties it needs only where it needs them?

Why not a 2 step emitter – spatially specific? different thickness and doping where needed? acknowledge that current flow is 2D not 1D

Why not replace with wider bandgap material?

Why not get rid of the emitter all together*

* On the front of the device


Industrially proven high efficiency Si solar cell concepts

Three commercial proven enhancements (full size wafer results) PERL/SE: passivated+selective emitter, rear localized contact HIT: ‘HJ intrinsic thin’ a-Si/c-Si heterojunction IBC: ‘interdigitated back contact’ rear emitter and base contact


Hi Eff concept #1: the 2-step ‘selective emitter’Conventional 1 stepthick emitter

2 step emitter: thinner n+ everywhere except under metal n++

AppliedMaterialswebsite

Increased blue response with thinner n+


SE option 1: laser doping + plating metal

http://www.photonics.com/Article.aspx?AID=40098


SE option 2: deposit thicker n++ then etch

back

• requires alignment of front metalto thicker n++ mesa


Thinner vs selective emitter: Voc, Isc, FF, Eff

Gauthier “Industrial Approaches of Selective Emitter on Multicrystalline Silicon Solar Cells”24th Eu-PVSEC (2009) 2-CV.5.46


Hi Eff #2 Heterojunction Solar Cell: deposited a-Si passivation layers reduce surface recombination

Device: n-type c-Si wafer and 5-10 nm PECVD a-Si layers (EG=1.7-1.8 eV)

(i) a-Si:H surface passivation layers (both sides)(p)a-Si:H emitter (front)(n)a-Si:H back contact (rear)All a-Si and contacts deposited <200°C (low $, less defects, no warping thin wafers)

High efficiency and VOC (Sanyo/Panasonic): η = 23% champion cells, 19% modulesVOC = 740mV

10nm (i)a-Si:H30nm (n)a-Si:H

10nm (p)a-Si:H

60nm ITO

300μm n-c-Si wafer

Rear Contact (Al)

Front Contacts (Ag)

Hole Current

Electron Current

EV

EFEC

hυ


Two modes of c-Si Surface Passivation by a-Si:H

c-Si Substrate a-Si:H film

EFEG,c-Si EG,a-Si:H

EC

EV

PECVD a-Si:H provides best passivation and processing < 300 °C, high VOC

Si surface cleaning critical to good passivation

Well-established, slow deposition rate, easily control thickness ~ 5-10 nm

Defect neutralization by H atoms:Reduce c-Si surface dangling bonds

Reduce recombination (IO), increase VOC

(n)c-Si Substrate (i)a-Si:H film

EF

EG,c-SiEG,a-Si:H

EC

EV

Field effect passivation:Increased band bending at junction

Repel/separate majority or minority carrierReduce Io, increase VOC


Hi Eff Si #3: Interdigited back contact (IBC) cell


Standard front junction vs all back contact


IBC spectral response higher in short (blue) and long (IR) wavelengths


Sunpower IBC: highest efficiency module


Integration of both device concepts: SHJ-IBC Cell

Interdigitated back contact (IBC) solar cell.

n-type c-Si

intrinsic a-Sip-type a-Si

TCO

intrinsic a-Sin-type a-Si

TCOSilicon heterojunction (SHJ) solar cell.

IBC-SHJ solar cell (IEC structure)

First publishedresults on SHJ-IBCBy IEC (APL 2007)

•intrinsic a-Si buffer•separate a-Si pand n regions


IEC Multichamber PECVD for HIT and IBC-SHJ

4 chambers plus 2 load lock, DC/RF/VHF plasmaMultiple substrate sizes (1x1 up to 12x12 inch)


Thin Film PV Common Features

Monolithic Integration via laser patterning: enabling technology

Lower efficiency: TF PV best suited for BIPV, large power plants

Status and Critical Issues Cu(InGa)Se2

CdTe A-Si/nc-Si (briefly)


Monolithic Series Interconnection : laser scribe Allows structuring of large area uniform thin film layers into series

connected junction diodes; critical technology for TF PV

Three laser scribing steps (patterning steps P1, P2, P3) P1) bottom conductor; P2) semiconductor junction; P3) top conductor

Width of cells determines module current (ISC), # in series determines VOC

Chapter 12, Handbook of Photovoltaic Science and Eng (Luque, Hegedus), Wiley 2011


TFPV applications: BIPV Appearance preferred for building-integrated PV

85kW Shell Solar Cu(InGa)Se2 in Wales

Semitransparent a-SiArchitectural skylight


Flexible PV for roll-out rooftop installation (USSC triple junction/SS)

Flexible a-Si on SS: BIPV (flex laminate)


4 MW of CdTe installed by Tucson Electric


15 MW of 3Sun Tandem Thin Si in Altomonte, Calabria Italy


Help from Bill Shafarman


Cu(InGa)Se2Thin Film Solar Cells


Why thin film CuInSe2 alloys for PV? Direct bandgap chalcopyrite materials with high absorption coefficient

Extraordinary compositional tolerance

Alloy with Ga, Al, Ag, S to engineer bandgap improve performance, TF tandem

Can be deposited on glass or light flexible substrates: polymer, foils

Highest device and module efficiency of any TF PV technology

Multiple deposition technologies with promise of scalability

Attracted considerable private investor funding

Outdoor module stability demonstrated


Cu(InGa)Se2 Thin Film PV Performance

Highest cell efficiency = 20.3% (ZSW 2010) Efficiency ≥ 18% from several laboratories Sub-module eff. = 17.8% with

area > 800 cm2 (Solar Frontier 2012) 12–14% module efficiency from

companies worldwide

Manufacturing Many companies with various approaches1. Reaction of metal precursors (2-step)

Low cost deposition of metals Batch process: “selenization”

2. Multi-source evaporation (1-step) In-line process, high temp

Substrate

Mo

Cu(InGa)Se2

Grid

CdSZnO:Al


Cu(InGa)Se2 Optical Absorption High optical absorption of sunlight

Direct bandgap Complete absorption in ~ 1 µm thickness (CdTe very similar) Reduces requirements for minority carrier transport

0

0.2

0.4

0.6

0.8

1

0.001 0.01 0.1 1 10 100 1000

Rel

ative

Abs

orpt

ion

thickness (µm)

Si

CIGS


Cu(InGa)Se2 Grain Structure Films are polycrystalline with rough surface

Grain size ~ 0.1 – 1 µm depends on deposition conditionse.g. substrate temperature during evaporation

But device performance is remarkably insensitive to grain size, morphology

1µm

Cu(InGa)Se2

Modeposited at 400°C deposited at 550°C

Wilson, Birkmire, Shafarman Proc. 33rd IEEE PVSC (2008)


CuInSe2 Alloys with wider EG: Al, Ga, S CuInSe2 has EG=1.0 eV, limits eff., major focus 20 yrs is to raise EG

Wide range of ternary, quaternary alloy options Recent focus on alloys with Ga/(Ga+In), S/(S+Se), Ag/(Ag+Cu)

Alloying changes EG also lattice constants (no epi!), band alignment

x = alloy fraction:Al/(In+Al)Ga/(In+Ga)S/(Se+S)

Ga/(In+Ga)a x=0b x=0.24c x=0.61


Increasing efficiency and VOC at higher EG Increasing EG with alloy (Ga, Ag, S) to push efficiency at EG >1.3 eV

Failure to capture benefit of larger EG due to VOC/ EG<1 is critical issue

Contreras et al, 37th IEEEE PVSC, Seattle 2011


Process 1: Elemental Co-evaporation Simultaneous delivery of elemental vapors

to hot substrate Makes higher efficiency devices than 2-step Independent control of each element

Ga/(In+Ga) gradient bandgap gradient

To vacuum pumpPbase ≈ 1x10-6 TorrPrun ≈ 2x10-5 Torr

Substrate HeaterSubstrate at 400-600°C

Film Growth MonitorThermal Evaporation

Sources for Cu, In, Ga, Se, (S)


IEC Cu(InGa)(SeS)2 Co-evaporation Five source system for Cu-In-Ga-Se-S

Boron nitride Knudsen cells Typical temperatures

T(Cu) = 1350°C T(In) = 1000°C T(Ga) = 1100°C T(Se) = 300°C

Source design and T control are critical features


Process 2: 2-step Precursor Reaction Advantages: lower cost, higher uniformity + materials utilization Many precursor deposition options with Cu, In, Ga –

sputtering – commercially available electrodeposition – high utilization, non-vacuum, batch ink printing – high utilization, non-vacuum, continuous

Reaction in hydride gases (H2Se, H2S) or elemental vapors (Se,S) Multi-step reaction pathway to form Cu(InGa)Se2

Mo/Cu/Ga/In Mo/Cu(InGa)Se2ReactionH2Se/H2S

or Se/S

400 - 600°C


Cu(InGa)Se2 Precursor Reaction IEC H2Se / H2S reactor

reaction in quartz tube of glass/Mo/Cu-In-Ga precursor layers atmospheric pressure with flowing H2Se / H2S / Ar / O2

Temperature-time cycle critical to uniformity, manufacturibility


CIGS Module Process Flow

CleanSubstrate

Mo dcsputtering

P1 laserscribe

CIGSdeposition

P3 mech.Scribe

EVA/glasslamination

CdS bathdeposition

HR ZnOdeposition

P2 mech.scribe

ZnO:Aldeposition

Modulecompletion

Attachbuss bars


Manu-facturer

DepositionTechnology

Champion product % apa

Current nameplate capacty MW/a

Deposition Process Pro´s

Deposition Process Con´s

comments

Manz (Würth)Solibro

1-stage co-evaporation

15.1

14.4

30 120

Simpler, more advanced process

Sacrifices efficiency Glass-glassCd- buffer

Global Solar Energy

3-stage co-evaporation

15 (cell)13 (mod)

Highest known TF module efficiency

Complex process SS substrate. glass/polymer

MiaSolé Reactive sputter 15.7 >40? good efficiency potential, rel. small capex exp.

Complex process SS substrate, cut + stitch, glass-glassCdS-dry

Solar Frontier,Stion/TSMC

2-step: Sputter+ H2Se/S-Selenization

SF: 17.8SF: 14.1 (manu)Stion: 14.5TSMC 15.1

980

5 + 135+300

advanced process, potentially higher CapEx

Sacrifices efficiencyHigher OpEx than evap.

glass-glassCdSglass-glassCd-free

Avancis, Hyundai

2-step: Sputter+Se-evap.+ RTP-cryst./H2S

30 + 100+100

Glass-glassCdS (Cd-free)

Solo Power 2-step electroplate-Selenization

15.1% cell13.5% mod

30 + 400 Good metal utilization, rel. low CapEx

Sacrifices efficiency SS substratePolymerCdS

Source: Markus Beck / Photon San Francisco‚ Feb. 2012 plus adds from the author

CIGS thin film manufacturing status: > 30MW real capacity


Two Current research issues: Cu(InGa)Se2

Fundamental understanding of relation between wide EG alloys and device performance with multisource evaporation

Control uniformity and reduce process time with Se/S reaction


1. New wide gap alloy (AgCu)(InGa)Se2 Ag addition to Cu(InGa)Se2 lowers melting temperature, better surface

mobility, potential for improved structural hence electronic quality

Ag increases bandgap by up to 0.25 eV,

Single phase over entire range of Ag–Cu and Ga–In alloying


Notable wide EG cell results with (AgCu) Cells: SLG/Mo/(AgCu)(InGa)Se2/CdS/ZnO/ITO/grid/MgF2

High Eff = 17.6% with Eg ≈ 1.3 eV High VOC = 890 mV with Eg ≈ 1.6 eV

Hanket, et al., Proc. 34th IEEE PVSC


2. H2Se/H2S reaction of Cu-Ga-In Precursors:Ga segregation at rear limits EG and Voc

0

10

20

30

40

50

60

0 20 40 60 80

com

positio

n (%

)

sputter time (min)

Se

Cu

In

Ga

Mo

S0

10

20

30

40

50

60

0 20 40 60 80co

mpo

sitio

n (%

)

sputter time (min)

Se

Cu

In

Ga

Mo

S

• 30’ H2Se@450°C, 15’ H2S@450°C• Complete H2Se reaction prior to H2S• Ga segregated at back, none at front• Low EG at front junction, low Voc

• 15’ H2Se@450°C, 15’ H2S@450°C• Partial H2Se reaction prior to H2S• Ga uniform, higher at front• Higher EG at front junction, higher Voc

Hankett et al, Proc 4th World PVSEC, 2006


Single step H2Se process vs. Three-step H2Se/H2S process

550

Time, min

Tem

p,

°C

20 50 10 10

1st step :H2Se

20 10

400

Time, min

Tem

p,

°C

20

Single step:H2Se

450

2nd step :Ar

3rd step :H2S

60 ~ 90 Mo

Mo

Ga accumulation

Ga homogenization

Process optimization Ga distributed uniformly with 3 step H2Se/H2S Major improvement in VOC and Eff.

Single step process

Three-step process

-0.2 0.0 0.2 0.4 0.6 0.8

-40

-20

0

20

J (m

A/c

m2 )

V (V)

Eff Voc Jsc FF Single-step : 8.3% 0.383 V 37.0 mA/cm2 58.7% 3-step : 14.2% 0.599 V 32.2 mA/cm2 73.5%


CdTe Thin Film Solar Cells

Help from Brian McCandless



Why CdTe TF solar cells? Chemically stable, simple phase diagram, easy surface passivation Film deposition by a variety of scalable techniques Optimized cells require post-dep halide (Cl) exposure at ~ 400C Easily adapted to monolithic integration Low cost: thin absorber, low cap ex equipment costs, high dep rate Best laboratory cell efficiency >17%, best module 14% (First Solar) Presently lowest price PV available (First Solar)

• First Solar <$0.75/W manufacturing cost• 2-3 hours from glass to module with 13% efficiency• Responsible for US lead in module manufacturing• Thin film success story!


Superstrate CdTe/CdS cell configuration

Glass superstrate (SLG or advanced)

SnO2 (comm or more complex TCO)

HR layer (intrinsic TCO, ~ 20 nm)

CdS (n-type, 30-50 nm)

CdTe (p-type, 2-4µm) + CdCl2 step

Contact (contains Cu as dopant)


CdTe/CdS heterojunction cell structure:grain boundaries, S-Te interdiffusion, QE

Contact(Cu+other)

p-CdTe

n-CdS

Zn2SnO4Cd2SnO4

glass 400 500 600 700 800 900

1.0

0.8

0.6

0.4

0.2

0

Wavelength (nm)Q

uant

um e

ffic

ienc

y

CdCl2 HTas-deposited

CdS depletionCdTe1‐xSx alloy

Bandgap shift


CdTe/CdS module processing

Clean glass/SnO2Substrate

DepositCdS, CdTe

FirstScribe

Post DepCdCl2 Treat

BackContact

SecondScribeThird

Scribe

Tabbing, Junct box

EncapsulateTest

CdTe Surface Etch


CdTe deposition technology

AtmosphericHigh Cl

O2

VacuumNo Cl

Low O2

T > 500°C T < 400°C

Spray ScreenPrint

CSSVT

PVDED

rf Sp

Golden PhotonMatsushita

Abound, USFFirst Solar, Calyxo

PrimeStar/GE, NREL, IEC

Canrom

BP Solar

XunLight 26


IEC CdTe Research using Vapor Transport Dep

CdTeSourceVapor Transport System CdCl2 Reactor

Develop process for Eff > 15% on moving glass substrate ( 3 cm/min) to provide basis for in-line manufacturing

Optimize: CdTe deposition, substrate, contacts, CdCl2 annealing Surface chemistry, interdiffusion, impurities, grain growth

Currently IEC CdTe work is proprietary; evaluating alternative glass, TCO, buffer layers


CdTe film growth: TSS, thickness, rateAFM 20 x 20 mSubstrate temp

Film thickness

Growth rate

500ºC5 m, 8 m/min

570ºC5 m, 8 m/min

550ºC1 m, 8 m/min

550ºC6 m, 8 m/min

550ºC23 m, 8 m/min

550ºC6 m, 81 m/min

Faceted morphology, grain size increases with substrate temperature

Grain size increases proportional with CdTe thickness

Grain size inversely proportional to CdTe growth rate


Fundamental CdTe issues Compensating defects → doping and defect control difficult

Difficult to achieve NA>5E14 cm3

High hole affinity → non-ohmic back contact (needs p+ Cu2Te) Unable to increase Voc>0.85V which is only 60% of EG

Highest efficiencies with non-commercial substrate Replace SLG with BSG glass ($) : more transparent, higher T deposition

Replace SnO2:F (FTO) with Cd2SnO4/Zn2SnO4 (CTO/i-ZnO)

Higher CdTe dep T allows improved grain structure (higher Voc, FF)


New substrates enable higher CdTe dep T higher Eff

[McCandless et al, to be submitted (2012)]

Commercial Tec10 SLG/SnO2:F/i-ZTO vs R&D GL/Cd2SnO4/i-ZTO

Record CdTe FF>81% With new substrates

13.5%

16.5%


Manu-facturer

DepositTech.

Champion product % apa

Current nameplate capacity MW/a

Depo Process Pro´s

Depo ProcessCon´s

module

First Solar Low Press Vapor Transport

14.4 modChamp lab cell: 17.3%

2,700closing several lines

Simple and matured process, high thruput

Global player,Quality ??

Glass-glass

Primestar/GE

“Thermal evap.“ 12.8 mod 30, started construct 400 MW, on hold

? Techn. Status ?

Glass-glass

Abound Solar(CSU)

Low PressThermal evap.

15.7 cell Started construct,Closed 2012

Glass in, module out.

Lower efficiency?

Glass-glass

Calyxo(Q-cell)

Atmos. press. thermal evap.

13.4%Champion lab cell: 16.2%

80 Potential low cost, high rate

Quality? Techn. Status ?

Glass-glass

Source: Schock / SNEC Shanghai‚ May 2012 plus adds from Dimmler 38th IEEE PVSC

CdTe thin film manufacturing status


Brief discussion of a-Si based multijunction PV

Steven Hegedus


Why amorphous Si (a-Si:H) for thin film PV? Unique among thin film PV technologies

Easily vary doping (p or n), bandgap, crystallinity (a-nc), thickness, Well-established commercially viable multijunction process (>20 yrs)

Minimal deposition steps: PECVD plus sputter back contact (<200°C)

Highest cell efficiency (3-junction a-Si/a-SiGe/nc-Si) : 14% (stabilized)

Commercial module stabilized efficiency (2J a-Si/nc-Si) : 9-10%

Least difference between best cell and typical module efficiency: Oerlikon, Sharp, AMAT have tandem 12% cell and 10% module

Challenge: native and light induced defectslow mobility+lifetime limit efficiency; even as lowest cost PV in market, cannot compete


Multijunction multibandgap a-Si solar cells

Chapter 12, Handbook of Photovoltaic Science and Eng (Luque, Hegedus), Wiley 2011

‘micromorph’a-Si/nc-Si tandemoptimum trade-offbetween cost and efficiency

Eff=6-7% Eff=9-11% Eff=12-13-% Eff=12-13%


Current a-Si PV commercial status: deathwatch ~ 10-15 companies bought Oerlikon or AMAT turn-key fab lines 2007-

2009 during Si feedstock shortage and PV price increase Low efficiency, high cap ex, new a-Si PV at disadvantage Most now closed (bankrupt), few operating in Asia Subsequent c-Si overcapacity and PV module price collapse squeezed a-

Si from the cost side (its strength) now multi-Si comparable cost Appl Matl closed their a-Si fab line 2010, Oerlikon Solar closed 2012

United Solar (USSC/ECD) flex roofing product: closed 2012 after 30 yr

Sharp (?), Panasonic, Kaneka, NexPower, Astraenergy-Chint; 3Sun (Italian JV Sharp-Enel) are leading players, ~9-10% efficient 2J 58 MW Sharp micromorph tandem installed in CA in 2012


Dispell Two PV Myths


I heard it takes more energy to make a solar module than they can ever produce?

NO!!!! How many years of operation before reach energy break-even point?

Energy payback is <1.5 years for today’s crystalline Si wafer modules, even less for next generation thin film modules

With 25 year warrantees, today’s PV modules will be net producers of clean, CO2-free electricity for at least 23 years!


I heard you would have to cover the country with solar modules to make any ‘real’ energy?

Total energy:200x200 miles(50% coverage)

Electricity only:100x100 miles(50% coverage)


Questions? Then buy this book!

2nd Edition (2011) of the mostcomprehensive PV book-1100 pages-6 new chapters-8 different cell technologies-TCO’s-performance characterization-batteries, inverters, system-policy, economics


Back-up slides


2012 TF PV industry expected production

0 200 400 600 800 1000 1200 1400 1600

First Solar - CdTe

Solar Frontier - CIGS

Sharp - thin Si

Astroenergy - thin Si

NexPower - thin Si

Trony - thin Si

Miasole - CIGS

T-Solar - thin Si

3Sun - thin Si

Solibro - CIGS

2102 Top Thin Film PV manufacturers

2012 MW produced

20

30

35

40

80

90

120

180

620

1530

Very fluid, obtained from Renewable Energy World on-line 6/4/2012


Double vs Triple Junction: United Solar/ECD

Guha, SPIE Photovoltaics 2009


Cadmium toxicity: perception problem Widely studied by Brookhaven Natl Lab and NREL Cd: lung, kidney, bone carcinogen CdTe: less soluble, more stable, less toxic Cd is by-product of Zn mining Choices: react Cd with Te and encapsulate behind glass in controlled

environment and generate clean energy; or leave it in exposed ore tailings

Not released to environment during roof-top residential fire EU: granted CdTe PV an exemption; politically vulnerable US: CdTe PV not classified as toxic waste (EPA) Japan, Korea: banned CdTe PV and closed research First Solar recycling/insurance program, “behind the fence” www.nrel.gov/cdte

Current Status of Solar Photovoltaic Technology …...2009/12/27 · Photonic Spectra Webinar “PV...

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Transcript of Current Status of Solar Photovoltaic Technology …...2009/12/27 · Photonic Spectra Webinar “PV...