07 veschetti ines
TRANSCRIPT
Overview of several bifacial
solar cells technologies
1
solar cells technologies
Y. Veschetti, R. Cabal, D. Munoz, S. Harrison, S. Gall
INES-CEA
Outline
•Two cells technologies compatible for bifacial application
���� a-Si:H/c-Si Heterojunction (HET) and PERT n-type Si
• HET R&D and Industrial development
���� Bifacial properties
• n-type PERT solar cells development
bifiPV Workshop Y. Veschetti
• n-type PERT solar cells development
���� Overview of various processes
���� Initial bifacial properties
���� Process adaptation to improve bifacial behaviour
•Conclusion et perspectives
Two bifacial solar cells on n-type silicon
SiO2 / SiNx
SiO2/
SiNx
Si(n)P- BSF
B-Emitter
Rear electrode
Front electrode
a-Si:H/c-Si heterojunction PERT n-type cell
Courtesy of Sanyo HITTM cell
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� nmax 23.7% (lab) � n = 21% prod [1]� T (°C) coefficient� Simple process < 10 steps � Low T - process� Thin substrate compatible
� nmax = 19.7% (lab) [2] � n ~ 18.5 - 19% prod� Simple process < 10 steps (potentially)� Compatible with p-type prod line� Thin substrate compatible
SiNxRear electrode
[1] 2AO.2.6, SANYO Electric, 26th EPVSEC (2011)
[2] Boescke, Bosch Solar, n-type workshop, Konstanz (2011)
Heterojunction development at INES
(n) c-Si
(i)/(p) a-Si:H
(i)/(n) a-Si:H
ITO
ITO
Ag
(n) c-Si
(i)/(p) a-Si:H
(i)/(n) a-Si:H
ITO
ZnO:B
Ag
Non bifacial configuration Bifacial configuration
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ITO
Ag
ZnO:B
Al
Best cell result certified S (cm²)Jsc
(mA.cm²)Voc (mV) FF (%) η (%)
Non bifacial cell (FZ) 105.0 36.3 732 77.9 20.7
Bifacial cell (Cz) 148.6 35.2 729 77.9 20.0
• Same amount of fabrication steps for both configuration
• Similar efficiency potential
���� Respective interest will be determined at the module level
HET: Bifacial characteristic
Increased reflectivity on the rear side due to a larger metal coverage
���� Substrate & ITO resistivity limitations
Illumination Reff (%)Jsc
(mA.cm²)Voc (mV) FF (%) η (%)
Front side 6.7 34.6 719 74.3 18.5
Rear side 9.6 31.8 717 74.4 17.0
90100
Inte
rnal
Qu
antu
m e
ffic
ien
cy
bifiPV Workshop Y. Veschetti
0102030405060708090
300 500 700 900 1100
Wavelength (nm)
Inte
rnal
Qu
antu
m e
ffic
ien
cy
(%)
Front side Rear side
Efficiency ratio
RS/FS = 92%
Room for improvement by
optimizing the a-Si:H(n+)
layers
• 35MW HET Labfab at INES Start up by the end of 2011
Towards Industrial Application in Europe :
Silicon Heterojunction solar cells :LABFAB
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• The PECVD and TCO line are working since december 2011
• Wet & screen printing hardware set up ongoing
• First cells after 3 months show high efficiency!!! >19%
• Uniformity tests ongoing on 90x90 cells 125PSQ
N-type PERT cell – Reference INES process
Si(n) Phosphorus BSF
Boron Emitter
Thermal SiO2\ SiNx
Rear s.p. grid
Front s.p. grid
Thermal SiO2 \ SiNx ARC
Texturing
Rear diffusion barrier
BCl3 emitter diffusion
BSG and barrier etching
POCl3 BSF diffusion
Front diffusion barrier
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POCl3 BSF diffusion
Dry oxidation
Front & Rear PECVD SiN
PSG and barrier etching
Front & Rear SP grid
Contact firing
148.6 cm² Cz-Si
Jsc
(mA/cm²)Voc (mV) FF (%) η (%)
Best 38.1 635.0 79.5 19.3
13 steps
Heading towards higher efficiencies
N Cz-Si
p+
N+
SiO2/SiN
N Cz-Si
p+
N+
SiO2/SiN
Implied Voc Cell Voc
Measurement of implied Voc
prior to metallization steps
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Gap between implied Voc and final cell Voc
SiO2/SiN SiO2/SiN
� Issues on Voc limitation:
Impact of SP metallization
Co-diffused n-type cell process3 fewer steps
Process simplification 1: co-diffusion
Reference n-type cell process
KOH texturing
Diffusion barrier
BCl3 diffusion
Barrier & BRL removal
Diffusion barrier
POCl3 diffusion
BSG/PSG removal
PECVD SiO2(B) deposition
Co-diffusion POCl3 furnace
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Cell resultJsc
(mA.cm²)Voc (mV) FF (%) η (%)
Cz (4Ω.cm; 180µm; 138.3cm²)
Ave. (x9) 37.2 631.1 79.2 18.6
best 37.2 632.9 80.2 18.9
BSG/PSG removal
Thermal oxidation
Front & rear SiN
Front & rear screen-printing
Co-firing
Process simplification 2: Ion Implantation
Standard n-type process Implantation process
Front B-implant
Back P-implant
Texturing
Rear side diffusion barrier
Front Boron diffusion
Barrier and BRL etching
Front diffusion barrier
Back POCl3 diffusion
Standard n-type process Implantation process
Front B-implant
Back P-implant
Texturing
Rear side diffusion barrier
Front Boron diffusion
Barrier and BRL etching
Front diffusion barrier
Back POCl3 diffusion
Collaborative project with
- Potentially lowest $/Wp solution
� Higher efficiency at lower cost
- Higher cell yield
� 4 Fewer steps and lower breakage
- Best wafer-wafer doping repeatability
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Thermal oxidation
Front and back PECVD SiN
Back P-implant
Thermal oxidation
Front/back metallization
Back POCl3 diffusion
Barrier and PSG etching
Thermal oxidation
Front and back PECVD SiN
Back P-implant
Thermal oxidation
Front/back metallization
Back POCl3 diffusion
Barrier and PSG etching
19.5% efficiency potential
� Process under development
� FF limitation being addressed
- Best wafer-wafer doping repeatability
� better binning, higher value
Cell resultImplied Voc (mV)
Voc (mV)Jsc
(mA.cm²)FF (%) η (%)
Cz (239cm²) 655 630.7 38.4 76.2 18.5
Co-firing
Cell results: 156PSQ Cz wafers
Bifacial performance of reference BCl3 process
80
100
Inte
rnal
Qu
antu
m
Illumination Reff (%) Voc (mV) Jsc (mA.cm²) FF (%) η (%)
Front side 5.3 630.7 38.6 78.3 19.1
Rear side 6.7 624.8 33.2 78.6 16.3
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Ratio efficiency
rearside/front side = 85%
� Higher reflectivity
� Heavy BSF non adapted0
20
40
60
80
300 500 700 900 1100
Wavelength (nm)
Inte
rnal
Qu
antu
m
Eff
icie
ncy
Front sideRear side
Process modification for bifacial application
Texturing
Rear diffusion barrier
BCl3 emitter diffusion
BSG and barrier etching
POCl3 BSF diffusion 840°C
Front diffusion barrier
� Identical grid on both side
� Use of wet oxidation at 700°C
� No distribution of P- BSF
� Lighter doping (60 Ω/�)
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Wet oxidation
Front PECVD SiN
PSG and barrier etching
Front & Rear SP grid
Contact firing
Rear PECVD SiN
P c
on
cen
tra
tio
n (
cm-3
)
Bifacial properties with adapted process
Illumination Voc (mV) Jsc (mA.cm²) FF (%) η (%)
Front side 627.4 38.8 77.0 18.7
Rear side 624.5 35.3 78.0 17.2
60
80
100
Inte
rnal
Qu
antu
m
effi
cien
cy (
%)
bifiPV Workshop Y. Veschetti
0
20
40
300 500 700 900 1100
Wavelength (nm)
Inte
rnal
Qu
antu
m
effi
cien
cy (
%)
Front sideRear side
Ratio η rear side/ front side = 92%
Positive effect of a lighter BSF
CONCLUSION
� Overview of two high efficiencies cell technologies HET & PERT cell
HETEROJUNCTION:
� Efficiency ratio RS/FS = 92%
� Room for improvement (work on a-Si:H(n+))
� Limitation of rear side reflectivity (grid density)
PERT cell:
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PERT cell:
� Description of simple fabrication processes
� Ratio of efficiency RS/FS = 92% using adapted process
� Room for improvement without degrading the front performance
� Perspectives:
Fabrication of bifacial modules
� B. Soria, presentation Tuesday at 11.20
Acknowledgements :Workshop organizers
LCP team
bifiPV Workshop Y. Veschetti
Merci de votre attention
1525/04/2012
Many thanks for your attention !
CONTACT : [email protected]