Thin Film CIGS Photovoltaics
Rommel Noufi
SoloPower, Inc.
5981 Optical Court, San Jose, CA 95138
www.solopower.com • email: rnoufi@solopower.com
2008 SoloPower
Acknowledgements:
Bulent Basol
SoloPower, Inc., California
Robert Birkmire
Institute of Energy Conversion, Delaware
Bolko von Roedern, Michael Kempe, and
Joel Del Cueto
National 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 Companies
Production of CIGS modules has also been demonstrated by:
Würth Solar, Showa Shell, Honda, and Global Solar Energy
(<20 MW manufactured)
Ascent, CO
DayStar Technologies, NY/CA
Energy Photovoltaics, NJ
Global Solar Energy, AZ
HelioVolt, TX
ISET, CA
MiaSole, CA
NanoSolar Inc., CA
SoloPower, CA
Solyndra, CA
Stion, CA
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Aleo Solar, Germany
AVANCIS, Germany
CIS Solartechnik, Germany
CISEL, France
Filsom, Switzerland
Honda, Japan
Johanna Solar Tech, Germany
Odersun, Germany
PVflex, Germany
Scheuten Solar, Holland
Showa Shell, Japan
Solarion, Germany
Solibro, Sweden
SULFURCELL, Germany
Würth Solar, Germany
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CIGS Device Structure
ZnO, ITO
2500 Å
CdS
700 Å
CIGS
1-2.5 µm
Mo
0.5-1 µm
Glass,
Metal Foil,
Plastics
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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
S2232B1-3
S2232B1-2
S2229A1-3
S2229A1-5
S2229B1-2
S2213-A1-3
0.704
0.713
0.717
0.720
0.724
0.731
0.740
34.33
33.38
33.58
32.86
32.68
31.84
31.72
79.48
79.54
79.41
80.27
80.37
80.33
78.47
19.2
18.9
19.1
19.0
19.0
18.7
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
theoretical
High
efficiency
range
Absorber band gap (eV)
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Closing the Gap between
Laboratory Cells and Modules
Primary Focus: Utilizing Lab Technology base to
translate 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.
CIGS Modules Process Sequence
Substrate
preparation
Base
Electrode
First
Scribe
Absorber
Third
Scribe
Top
Electrode
Second
Scribe
Junction
Layer
External
Contacts
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Encapsulation
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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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Challenges
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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,
Thin Cells Summary
e.g. threshold
thickness nonuniformity,
pin-holes
- Challenge is to
reduce thickness
and maintain
performance
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0.4 µm cell - Optical
Absorption
80
%T, A, QE
60
T
QE
40
20
R of Cell
0
400
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600
800
1000
Wavelength (nm)
1200
1400nm
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 Advances
• SoloPower has developed a low cost electrodeposition process to manufacture CIGS solar cells
and modules
V
electrolyte
anode
• A conversion efficiency approaching 14% has been
confirmed at NREL
• Modules have been manufactured demonstrating
process flow
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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
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C2318
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SoloPower Confidential
Future Commercial Module Performance
Based on today’s champion cell results and a module/cell-ratio of 80%
Future commercial
performance
Relative
Performance
(s.p. Si =1)
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)
Technology
Relative-cost/relativeperformance (50% thin film
cost advantage)
Source: Bolko Von Roedern, PVSC 2008, IEEE May 12,2008, San Diego
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Best Production-Line
PV Module Efficiency Values
Ranked Module
Efficiency (%)
19.3
(non-stan)
17.4
(non-stan)
14.4
(non-stan)
14.2
(multi)
14.1
(mono)
13.9
(mono)
13.8
(multi)
13.7
(multi)
13.4
(mono)
13.4
(mono)
13.4
(multi)
13.1
(ribbon)
11.3
(CIGS)
Same module with
lowe st power rating
Descriptio n of best module
SunPower 315 (SunPower rear-point contacted cells, mono-Si)
Tcoeff = -0.38 %/C, VOC/cell = 673 mV
Sanyo HIP -205BAE (single crysta l CZ Si, HIT
(Tcoeff = -0.30 %/C), VOC/cell = 717 mV
Advent Solar Advent 240 (emitter wrap thru multi-Si)
Tcoeff= -0.52%/C, VOC/cell = 610 mV
Kyocera KC200GHT-2 (cast multi-Si diffused cells)
Tcoeff.(only given for Voc, -0.123 V/C), VOC/cell = 609 mV
Sharp NU-185 (mono-Si, standard)
-0.485%/C, VOC/cell = 629 mV
BP4175 (mono-Si – standard)
Tcoeff= -(0.5±0.05) %/C, VOC/cell = 606 mV
BP BP3230 multi-Si standard cells)
Tcoeff= -(0.5±0.05) %/C, VOC/cell = 607 mV
Sharp ND-224-U1 (multi-Si, diffused)
Tcoeff=-0.485%/C , VOC/cell = 610 mV
SolarWorld Sunmodule 175/165/155 (mono-Si “Shell”)
Tcoeff.: VOC= -0.33V/C, VOC/cell = 617 mV
Also as Sharp 216, then 13.3% efficient 25-y ltd
warranty
Also SW 155, efficiency 11.9%
Power-warranty 12/90%, 25/80%
SunTech STP 260S-24V/b (mono-Si diffused cells) VOC/cell = 615 mV
25-y ltd warranty
Solar World AG SW 225 (multi-Si) Tcoeff.: VOC= -0.33V/C,
VOC/cell = 613 mV
Evergreen Solar ES 195 (string ribbon Si)
Tcoeff= -0.49%/C, VOC/cell = 609 mV
Solibro SL1-85 (CIGS)
Tcoeff=-0.45%/C
Also SunPower 305, efficiency 18.7%
Also HIP-180BA E, efficiency 15.3%
Also A dvent 210, efficiency 12.6%
Only one rating listed,
Also Sharp NU-170, efficiency 13.0%
Also BP4165, efficiency 13.1%
Also BP3210, efficiency 12.6%, 25-y ltd warranty
Also SW 200, efficiency 11.9%
Also ES-180 efficiency 12.0%
Also as SL1-60, then eff. is 8.0%
From Manufacturers’ Web Sites Compiled by Bolko von Roedern, September 2008
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Best Production-Line
PV Module Efficiency Values (cont.)
Ranked Module
Efficiency (%)
11.2
(CIGS)
11.0
(CIS)
10.4
(CdTe)
9.0
(CdTe)
8.5
(a-Si/nc-Si)
8.2%
(a-Si/nc-Si)
8.0
(CIGS)
6.3
(a-Si 1-j)
6.3
(a-Si 3-j)
6.3
(a-Si 1-j)
5.9
(a-Si 1-j)
5.9
(a-Si/a-Si)
5.3
(a-Si/a-Si)
Same module with
lowe st power rating
Descriptio n of best module
Honda HEM125PA (CIS)
WürthSolar WS GOO25 E080 (CIS)
Tcoeff.= -0.36 %/C
First Solar FS-275 (CdTe)
Tcoeff= -0.25 %/C Voc/cell = 773 mV
Calyxo CX 65 (CdTe)
Tcoeff= -0.25 %/C
Sharp NA-901-WP (90-W) (amorphous/nanocrystalline Si tandem)
Tcoeff=-0.24%/C
Sontor SN2-145 (amorphous/nanocrystalline Si tandem)
Tcoeff=-0.40%/C
GSE Solar GSE 33060
Tcoeff=-0.5%/C
Mitsubishi Heavy MA100 T2 (single j. a-Si, VHF deposition),
Tcoeff.= -0.2 %/C
Uni-Solar PVL 136 (triple-j. amorphous silicon roofing laminate),
Tcoeff = - 0.23%/C
Kaneka T-SC(EC)-120 (single-j. a-Si)
No Tcoeff. given
Ersol Nova-T GOO25 E080 (single-j. a-Si)
Tcoeff.= -0.31 %/C
Schott Solar ASI-TM86 (same-bandgap double junction a-Si)
Tcoeff = - 0.20%/C
EPV EPV-42 (same-bandgap double junction a-Si)
Tcoeff = - 0.19%/C
Also available as 115W, then 10.3% efficient
Also WS GOO25 E075, efficiency 10.3%
(warranty 20/80%)
Also FS-260, efficiency 8.3% (25-y ltd warranty)
Also as CX 35 , then eff. is 4.9%
Also Sharp NA-801 (80W)
Efficiency 7.6% (warranty: 10/90%, 20/80%)
Also as SN2-125 , then eff. is 7.0%
Only one rating, but +/-15% power spec,
25-y ltd warranty
Only one rating
(warranty 20/80% warranty)
Also as 124 W, eff. 5.7%
(20-year ltd warranty)
Only one rating
(ltd warranty 25/80%)
Also available as 70 W, eff. then 4.9%
From Manufacturers’ Web Sites Compiled by Bolko von Roedern, September 2008
2008 SoloPower
Also ASI TM78, eff 5.4%
20-y ltd warranty
Also EPV-40, eff 5.1%
(warranty 25/80%)
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
DOE, Solar America Initiative Projections and Goals
• Costs are
constant 2005
dollars
• Residential and
commercial are
cost to customer
Solar Electricity cost
• Utility is cost of
generation
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CIGS Manufacturing
Requirements for a CIGS absorber film growth technique for high
efficiency devices include:

For high quality
–
Stoichiometric control
[Cu/(Ga+In), Ga/(Ga+In), S/(S+Se)]
– Good microstructure
– Bandgap control

For low cost
–
–
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Low cost equipment
High materials utilization
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