- Flexible PV modules for BIPV - Potential for cost reductions and aesthetic integration - Challenges for processing thin silicon wafer Dr. Andrew Skumanich, SolarVision Consulting

1. Thin Films and Thin Wafers:
Challenges and
Opportunities with BIPV
PV Summit
June 3 rd 2009
Andy Skumanich, Ph.D.
SolarVision Consulting
SVC 2009 PV Summit Conference Page 1

2. Outline
Opportunities and challenges
• Market potential for BIPV
– Flexible PV modules
• Challenges
– Potential for cost reduction and aesthetic integration
• Thin film trajectory: CE and cost
– Various types including CIGS
• Ultra-thin wafer trajectory: thickness, CE, and cost
– PV processing sequence
– Handling considerations
• Conclusions
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3. Market Opportunities
• General PV forecast: 6-9 GW in 2010
• Demand for glass: 2010 – 1Billion m2 WW
– Take 1/10% as BIPV, 10% CE
1GW of PV glass
• Roof-tops residential: coverage by PV
– 7 million new houses in typical year
– If 1/10% have BIPV roof, 10%CE
1GW of rooftop PV for residential
• BIPV could potentially be a major market driver
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4. SVC 2009 PV Summit Conference Page 4

5. BIPV Market Requirements
• Aesthetics, cost
• Customizability
• Product availability
• Product features: Flexibility, Shape, etc.
• Market opportunity for flexible TF, and c-Si foils
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6. Challenges
• Thin Film:
– Improved efficiency
– Flexible substrate extends applications – maintain CE
– Viability of materials without exchange
• Wafer based c-Si:
– Foils which are flexible and robust
– Improved efficiency for ultra-thin wafers – recover CE
– Processing of wafers-to-cells
• Common
– Customizability in design
– Product range
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7. Turn-key Landscape: TF & c-Si
a-Si and CIGS CdTe c-Si
Tandem
• Oerlikon (11) • Centrotherm • (Roth & Rau) Full chain:
• AMAT (14) • Centrotherm
• Ulvac (3) • Schmid
• Other misc
Multiple sub-
lines
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8. Thin Film CE gains
• CIGS starting to show promise
– Turnkey line from Centrotherm
• a-Si needs to achieve >10% capability
• CdTe needs to confirm reliability
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9. Centrotherm CIGS Turn-key
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10. Value of thin wafers for c-Si PV
• Potential benefits
– Improved theoretical conversion efficiency
– Potentially improved flexibility below 100um
C.E. vs Thickness (R&D data) Strength vs Thickness
CZ P-type !!
(w/ B-O)
Post-
degradation
??
S. Schoenfelder EuroSim, 2006
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11. Cell Efficiency vs. Thickness
Conversion
Efficiency %
24 SunPower
Solar Cell
22
Conventional
20
Solar Cell
18 Cost reduction
16
14
12
10
350 300 250 200 150 100
Cell Thickness (microns)
Solar cell thickness reduction is a key cost reduction path. SunPower solar cell
efficiency improves as wafer thickness decreases versus conventional solar cells
which become less efficient on thinner wafers.
11
SVC 2009 PV Summit Conference Page 11

12. Wafer Thickness Roadmap
350
Multi -
300 crystalline
Wafer Thickness (um)
250
200
150 SunPower
150
120
mono c-Si,
100 (125mm)
Mono -
50 crystalline
0
2002 2004 2006 2008 2010 2012
(Source: NREL Silicon Strategy, Dick Swanson – SunPower, SVC)
12
SVC 2009 PV Summit Conference Page 12

13. Cell Efficiency Roadmap
Cell Efficiency History and NREL Plan
Conversion Efficiency
25
SunPower
mono c-Si,
20
CE (%)
15
Mono -
10 crystalline
Multi -
crystalline
5
0
2002 2004 2006 2008 2010 2012
(Source: NREL Silicon Strategy, Dick Swanson – SunPower, SVC)
13
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14. Ultra-thin wafer processing
• Aggressive activities world wide
– EU: Fraunhofer Institute
– Japan: NEDO
– USA: various including commercial companies
• Key developments: e.g. back surface treatment
– Example is GIT – Dr. Ajeet Rohatgi
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15. GIT modeling for sub 100um wafers
• Bulk lifetime, thickness, BSRV and BSR targets for achieving 19-20% efficiency cells with
screen printed front contacts
21
Our Goal
20
19
Efficiency (%)
18
17 Current Status
lifetime=100us, BSRV=50cm/s, BSR=97%
16
lifetime=100us, BSRV=400cm/s, BSR=65%
15 lifetime=25us, BSRV=50cm/s, BSR=97%
lifetime=25us, BSRV=400cm/s, BSR=65%
14
0 100 200 300 400 500 GIT Dr.
Solar Cell Thickness (um)
Ajeet
Rohatgi
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16. Roadmap to 20%-efficient c-Si solar
cells with screen printed contacts
22%
20.1% 20.0%
20% 19.3%
18.2%
18%
17.0%
Efficiency
16%
14%
12%
10%
Current Solar Improved Text, BSR (97%) High Sheet Res. Reduce Cell
Cell AR & SP BSRV Emitter (R=100 Thickness (100
GIT Dr.
(Ref=1.04% (100cm/s) ohm/sq) µm) Ajeet
FF=79.1% Rohatgi
M.C.=5.0)
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17. New Process Vs Full Al BSF IQE & RetroRefl
100 100
90 90
80 80
New Full Al
70 Process BSF
70
Reflectance (%)
60 Voc(mV) 652 639 60
IQE (%)
Jsc(mA/cm 2) 39.4 37.9 New Process
50 50
FF(%) 78.1 78.9
40 Eff (%) 20.1 19.1 40
30 30
Full Al BSF
20 20
10 10 GIT Dr.
Ajeet
0 0
300 400 500 600 700 800 900 1000 1100 1200
Rohatgi
Wavelength (nm)
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18. IV-curve for the best Screen Printed
New Process cell
0.16
0.14
0.12
0.10
? : 20.1 %
Isc (A)
0.08 VOC : 652 m V
JSC : 39.4 mA/cm2
0.06 FF : 78.1 %
0.04
0.02
0.00 GIT Dr.
0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 Ajeet
Voc (mV)
Rohatgi
Dielectric passivated rear LBSF raised the efficiency from 19.1 to 20.1%
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19. Handling issues
• Breakage
– Of course the major concern for module manufacturers
• Warped wafers cause issues
– Ultra thin may have benefits and drawbacks
• Start-stop needs to be abrupt for high tpt
– Wafers act like “wings” during motion
• Multiple challenges for handling
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20. Alternative Companies for Handling
• Equipment: Automation Technology Inc:
– Bernoulli grippers
– But still not developed
• Researchers at the Texas Manufacturing Assistance Center (University
of Texas, Arlington)
– prototype air system able to both acquire wafers from a stack and move
them along a track with no moving components
– contrasts with Bernoulli grippers which only acquire wafers and must use
manipulators and robotic elements to move wafers
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21. Summary
• Decreasing thickness still moving forward
– Market leaders driving to wafers 150um and then below
– New improvements for thin films (CIGS specifically)
• Market forces will be pushing prices down
– Foreseeable future: more pressure on cost reduction
– Companies with tech advantages will survive
• Thin Film are steadily developing improved CE with
CIGS leading in CE, (not in market)
– Multiple challenges: higher CE >10% at low cost production
• Thin, and ultra-thin wafers now are driving processing
– Mulitple challenges: maintain CE below 100um, breakage
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22. Conclusions
• Industry needs to drive metrics and dimensions
– BOS may be substantially lower for frame and labor
– May be closer to “grid parity” with lower BOS
• Increased focus on BIPV is also required
• Also, product portfolio needs to be expanded
– Flexible, multi-dimensional, etc.
• Current development capabilities can open up the
BIPV market in increase the demand for TF and ultra-
thin c-Si
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23. TF BIPV
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24. SolarVision Consulting
Contact: Dr. Andy Skumanich
AndySkumanich@gmail.com
www.solarvisionconsulting.com
SVC 2009 PV Summit Conference Page 24