2008 SoloPower

Thin Film CIGS Photovoltaics

Rommel NoufiSoloPower, Inc.

5981 Optical Court, San Jose, CA 95138www.solopower.com • email: rnoufi@solopower.com

2008 SoloPower 2

Acknowledgements:

Bulent BasolSoloPower, Inc., California

Robert BirkmireInstitute of Energy Conversion, Delaware

Bolko von Roedern, Michael Kempe, and

Joel Del CuetoNational Renewable Energy Laboratory, Colorado

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Outline

Status of the Technology

– Laboratory cells

– Modules

Challenges Ahead

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Status of PV

• 3700 MW produced world wide

• 266 MW produced in the US

• Thin Film Market Share: 10% world wide, 65% in the US

Source: PV News, Photon International, Navigant Consultants

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Status of Thin Film PV

• Currently, FIRST SOLAR [ CdTe ] is the largest Thin Film manufacturing company in the US

- 277 MW in 2007- 910 MW expected in 2009

• Demonstrated the viability of Thin Film PV- High Throughput- Large Scale- Low Cost per Watt

Source: First Solar.com

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PVNews Reported US Production thru 2007

Source: PVNews

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CIS PV CompaniesProduction of CIGS modules has also been demonstrated by:

Würth Solar, Showa Shell, Honda, and Global Solar Energy(<20 MW manufactured)

Ascent, CODayStar Technologies, NY/CAEnergy Photovoltaics, NJGlobal Solar Energy, AZHelioVolt, TXISET, CAMiaSole, CANanoSolar Inc., CASoloPower, CASolyndra, CAStion, CA

Aleo Solar, GermanyAVANCIS, GermanyCIS Solartechnik, GermanyCISEL, FranceFilsom, SwitzerlandHonda, JapanJohanna Solar Tech, GermanyOdersun, Germany PVflex, GermanyScheuten Solar, HollandShowa Shell, JapanSolarion, GermanySolibro, SwedenSULFURCELL, GermanyWürth Solar, Germany

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ZnO, ITO2500 Å

CdS700 Å

Mo0.5-1 µm

Glass,Metal Foil,

Plastics

CIGS1-2.5 µm

CIGS Device Structure

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Best Research-Cell Efficiencies

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Parameters of High Efficiency CIGS Solar Cells

Sample Number Voc (V) Jsc (mA/cm2) Fill factor (%) Efficiency (%)

M2992-11 0.690 35.55 81.2 19.9 (World Record)

S2212-B1-4 0.704 34.33 79.48 19.2

S2232B1-3 0.713 33.38 79.54 18.9

S2232B1-2 0.717 33.58 79.41 19.1

S2229A1-3 0.720 32.86 80.27 19.0

S2229A1-5 0.724 32.68 80.37 19.0

S2229B1-2 0.731 31.84 80.33 18.7

S2213-A1-3 0.740 31.72 78.47 18.4

Tolerance to wide range of molecularity

Cu/(In+Ga) 0.95 to 0.82

Ga/(In+Ga) 0.26 to 0.31

Yields device efficiency of 17.5% to 19.5%

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“Champion” Modules

Company Device Aperture Area (cm2)

Efficiency* Power

(W)

Würth Solar CIGS 6500 13.0 84.6

Shell Solar GmbH CIGSS 4938 13.1 64.8

Showa Shell CIGS 3600 12.8 44.15

Shell Solar CIGSS 7376 11.7 86.1*

Global Solar CIGS 8390 10.2 88.9*

First Solar CdTe 6623 10.2 67.5*

*Third party confirmed

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Optical Band-Gap/Composition/Efficiency

Absorber band gap (eV)

theoretical

High efficiency range

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Closing the Gap between Laboratory Cells and Modules

Primary Focus: Utilizing Lab Technology base totranslate results to manufacturing

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CIGS Modules are Fabricated On:

I. Soda lime glass as the substrate; cells are monolithically integrated using laser/mechanical scribing.

Courtesy of Dale Tarrant, Shell Solar

Monolithic integration of TF solar cells can lead to significant manufacturing cost reduction; e.g., fewer processing steps, easier automation, lower consumption of materials.

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CIGS Modules are Fabricated On: (cont.)

The number of steps needed to make thin film modules are roughly half of that needed for Si modules. This is a significant advantage.

Substratepreparation

Base Electrode

AbsorberFirstScribe

ThirdScribe

TopElectrode

JunctionLayer

SecondScribe

ExternalContacts Encapsulation

CIGS Modules Process Sequence

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CIGS Modules are Fabricated On: (cont.)

II. Metallic web using roll-to-roll deposition; individual cells are cut from the web; assembled into modules.

III. Plastic web using roll-to-roll deposition; monolithic integration of cells.

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ChallengesChallenges

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Long-Term Stability (Durability)

• Improved module package allowed CIGS to pass damp heat test (measured at 85°C/85% relative humidity).

• CIGS modules have shown long-term stability. However, performance degradation has also been observed.

• CIGS devices are sensitive to water vapor; e.g., change in properties of ZnO.

- Thin Film Barrier to Water Vapor

- New encapsulants and less aggressive application process

• Stability of thin film modules are acceptable if the right encapsulation process is used.

• Need for better understanding degradation mechanisms at the prototype module level.

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Processing Improvements:

I. Uniform Deposition over large area:

(a) significant for monolithic integration

(b) somewhat relaxed for modules made from individual cells

II. Process speed and yield: some fabrication approaches have advantage over others

III. Controls and diagnostics based on material properties and film growth: benefits throughput and yield, reliability and reproducibility of the process, and higher performance

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Processing Improvements: (cont.)

IV. Approaches to the thin film CIGS Deposition

1. Multi-source evaporation of the elements

- Produces the highest efficiency

- Requires high source temperatures, e.g., Cu source operates at 1400°-1600°C

- Inherent non-uniformity in in-line processing

- Fast growth rates my become diffusion limited

- Complexity of the hardware with controls and diagnostic

- One of a kind hardware design and construction

- Expensive

- Throughput, and material utilization need improvement

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Processing Improvements: (cont.)

IV. Approaches to the thin film CIGS Deposition (cont.)

2. Reaction of precursors in Se and/or S (Selenization)to form thin film CIGS: two stage process- Variety of materials delivery approaches:

(a) sputtering of the elements (b) electroplating of metals or binaries (c) Printing of metal (or binaries) particles on

substrate

- Reaction time to form high quality CIGS films is limited by reaction/diffusion- Modules on glass are processed in batch mode in order to deal with long reaction time- Flexible roll-to-roll requires good control of Se vapor and reaction speed- Ga concentration thru the film is inhomogeneous limiting performance

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Processing Improvements: (cont.)

V. Reduction of the thickness of the CIGS film- Reduces manufacturing costs: higher throughput and less

materials usage

- More sensitive to yield, e.g. threshold thickness non-uniformity, pin-holes

- Challenge is to reduce thickness and maintain performance

Thin Cells Summary

2008 SoloPower

0.4 µm cell - Optical

80

60

40

20

0

%T

, A, Q

E

1400nm12001000800600400Wavelength (nm)

QE

Absorption

T

R of Cell

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Toward Low Cost

• Module performance is a significant determining factor of cost

• Cell processing affects performance

• The benefits of each process and how it is handled in manufacturing need to be assessed

• To date, relatively high cost methods adapted for manufacturing

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• SoloPower has developed a low cost electro-deposition process to manufacture CIGS solar cells and modules

• A conversion efficiency approaching 14% has been confirmed at NREL

• Modules have been manufactured demonstrating process flow

electrolyteanode

VV

SoloPower Advances

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The Electrodeposition Process

• Hardware is low cost

• Can be high throughput once the hardware is tuned to the specifics of the process

• Near 100% material utilization

• Pre-formed expensive materials are not required, e.g. sputtering targets, nano-particles

• Crystallographically oriented CIGS films with good morphology and density have been demonstrated

• Thickness and composition control of the deposited films are integral part of the process

• Readily scalable

2008 SoloPower2008 SoloPower SoloPower Confidential

C2318

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Future Commercial Module Performance

Based on today’s champion cell results and a module/cell-ratio of 80%

TechnologyFuture commercial

performance

Relative Performance

(s.p. Si =1)

Relative-cost/relative-performance (50% thin film

cost advantage)

Silicon (non-stand)

19.8% 1.18 0.85 (competitive)

Silicon (standard)

17.0% 1.00 1.00 (reference)

CIS 15.9% 0.94 0.53 (highly competitive)

CdTe 13.2% 0.78 0.64 (highly competitive)

a-Si (1-j) 8.0% 0.47 1.06 (about the same)

a-Si (3-j) (or a-Si/nc-Si)

9.7% 0.57 0.88 (competitive)

Source: Bolko Von Roedern, PVSC 2008, IEEE May 12,2008, San Diego

2008 SoloPower

Best Production-LinePV Module Efficiency Values

Ranked Module Efficiency (%)

Description of best module Same module with

lowest power rating

19.3 (non-stan)

SunPower 315 (SunPower rear-point contacted cells, mono-Si) Tcoeff = -0.38 %/C, VOC/cell = 673 mV

Also SunPower 305, efficiency 18.7%

17.4 (non-stan)

Sanyo HIP-205BAE (single crystal CZ Si, HIT (Tcoeff = -0.30 %/C), VOC/cell = 717 mV Also HIP-180BAE, efficiency 15.3%

14.4 (non-stan)

Advent Solar Advent 240 (emitter wrap thru multi-Si) Tcoeff= -0.52%/C, VOC/cell = 610 mV

Also Advent 210, efficiency 12.6%

14.2 (multi)

Kyocera KC200GHT-2 (cast multi-Si diffused cells) Tcoeff.(only given for Voc, -0.123 V/C), VOC/cell = 609 mV

Only one rating listed,

14.1 (mono)

Sharp NU-185 (mono-Si, standard) -0.485%/C, VOC/cell = 629 mV

Also Sharp NU-170, efficiency 13.0%

13.9 (mono)

BP4175 (mono-Si – standard) Tcoeff= -(0.5±0.05) %/C, VOC/cell = 606 mV

Also BP4165, efficiency 13.1%

13.8 (multi)

BP BP3230 multi-Si standard cells) Tcoeff= -(0.5±0.05) %/C, VOC/cell = 607 mV

Also BP3210, efficiency 12.6%, 25-y ltd warranty

13.7 (multi)

Sharp ND-224-U1 (multi-Si, diffused) Tcoeff=-0.485%/C , VOC/cell = 610 mV

Also as Sharp 216, then 13.3% efficient 25-y ltd warranty

13.4 (mono)

SolarWorld Sunmodule 175/165/155 (mono-Si “Shell”) Tcoeff.: VOC= -0.33V/C, VOC/cell = 617 mV

Also SW 155, efficiency 11.9% Power-warranty 12/90%, 25/80%

13.4 (mono)

SunTech STP 260S-24V/b (mono-Si diffused cells) VOC/cell = 615 mV 25-y ltd warranty

13.4 (multi)

Solar World AG SW 225 (multi-Si) Tcoeff.: VOC= -0.33V/C, VOC/cell = 613 mV

Also SW 200, efficiency 11.9%

13.1 (ribbon)

Evergreen Solar ES 195 (string ribbon Si) Tcoeff= -0.49%/C, VOC/cell = 609 mV

Also ES-180 efficiency 12.0%

11.3 (CIGS)

Solibro SL1-85 (CIGS) Tcoeff=-0.45%/C

Also as SL1-60, then eff. is 8.0%

From Manufacturers’ Web Sites Compiled by Bolko von Roedern, September 2008

2008 SoloPower

Best Production-LinePV Module Efficiency Values (cont.)

Ranked Module Efficiency (%)

Description of best module Same module with

lowest power rating

11.2 (CIGS)

Honda HEM125PA (CIS)

Also available as 115W, then 10.3% efficient

11.0 (CIS)

WürthSolar WS GOO25 E080 (CIS) Tcoeff.= -0.36 %/C

Also WS GOO25 E075, efficiency 10.3% (warranty 20/80%)

10.4 (CdTe)

First Solar FS-275 (CdTe) Tcoeff= -0.25 %/C Voc/cell = 773 mV

Also FS-260, efficiency 8.3% (25-y ltd warranty)

9.0 (CdTe)

Calyxo CX 65 (CdTe) Tcoeff= -0.25 %/C

Also as CX 35 , then eff. is 4.9%

8.5 (a-Si/nc-Si)

Sharp NA-901-WP (90-W) (amorphous/nanocrystalline Si tandem) Tcoeff=-0.24%/C

Also Sharp NA-801 (80W) Efficiency 7.6% (warranty: 10/90%, 20/80%)

8.2% (a-Si/nc-Si)

Sontor SN2-145 (amorphous/nanocrystalline Si tandem) Tcoeff=-0.40%/C

Also as SN2-125 , then eff. is 7.0%

8.0 (CIGS)

GSE Solar GSE 33060 Tcoeff=-0.5%/C

Only one rating, but +/-15% power spec, 25-y ltd warranty

6.3 (a-Si 1-j)

Mitsubishi Heavy MA100 T2 (single j. a-Si, VHF deposition), Tcoeff.= -0.2 %/C

Only one rating (warranty 20/80% warranty)

6.3 (a-Si 3-j)

Uni-Solar PVL 136 (triple-j. amorphous silicon roofing laminate), Tcoeff = - 0.23%/C

Also as 124 W, eff. 5.7% (20-year ltd warranty)

6.3 (a-Si 1-j)

Kaneka T-SC(EC)-120 (single-j. a-Si) No Tcoeff. given

Only one rating (ltd warranty 25/80%)

5.9 (a-Si 1-j)

Ersol Nova-T GOO25 E080 (single-j. a-Si) Tcoeff.= -0.31 %/C

Also available as 70 W, eff. then 4.9%

5.9 (a-Si/a-Si)

Schott Solar ASI-TM86 (same-bandgap double junction a-Si) Tcoeff = - 0.20%/C

Also ASI TM78, eff 5.4% 20-y ltd warranty

5.3 (a-Si/a-Si)

EPV EPV-42 (same-bandgap double junction a-Si) Tcoeff = - 0.19%/C

Also EPV-40, eff 5.1% (warranty 25/80%)

From Manufacturers’ Web Sites Compiled by Bolko von Roedern, September 2008

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Further Reading Sources

“Accelerated UV Test Methods for Encapsulants of Photovoltaic Modules”

“Stress Induced Degradation Modes in CIGS Mini-Modules”Michael D. Kempe et al, Proceedings of the 33rd IEEE,PVSC, May 11, 2008, San Diego

“Modeling of Rates of Moisture Ingress into Photovoltaic Modules” Michael D. Kempe, Solar Energy Materials & Solar Cells, 90 (2006) 2720–2738

“Stability of CIS/CIGS Modules at the Outdoor Test Facility Over Two Decades”J.A. del Cueto, S. Rummel, B. Kroposki, C. Osterwald, A. Anderberg,

Proceedings of the 33rd IEEE,PVSC , May 11, 2008, San Diego

“Pathways to Improved Performance and Processing of CdTe & CuInSe2 Based Modules” Robert W. Birkmire, Proceedings of the 33rd IEEE,PVSC, May 11, 2008, San Diego

“The Role of Polycrystalline Thin-Film PV Technologies in Competitive PV Module Markets” Bolko von Roedern and Harin S. Ullal,

Proceedings of the 33rd IEEE,PVSC , May 11, 2008, San Diego

“High Efficiency CdTe and CIGS Thin Film Solar Cells: Highlights and Challenges” Rommel Noufi and Ken Zweibel

Proceedings of the 4th WCPEC, May 7, 2006, Hawaii

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The End

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PV Energy Cost

• Costs are constant 2005 dollars

• Residential and commercial are cost to customer

• Utility is cost of generation

Solar Electricity cost

DOE, Solar America Initiative Projections and Goals

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CIGS Manufacturing

For high quality– Stoichiometric control

[Cu/(Ga+In), Ga/(Ga+In), S/(S+Se)]– Good microstructure – Bandgap control

For low cost– Low cost equipment– High materials utilization

Requirements for a CIGS absorber film growth technique for high efficiency devices include: