Front And Back Contacts For Flexible CIGS Solar Cells Torsten Winkler, Sascha Kreher FHR Anlagenbau GmbH 01458 Ottendorf-Okrilla, Germany Contact:
[email protected]
Front And Back Contacts For Flexible CIGS Solar Cells
Extended Abstract Providing back and front contact for CIGS solar cells seems to be a kind of standard task for proven machine supplier as well as for cell manufacturer. Although both technologies are widely used, they all have their limitations and always some new aspects need to be considered. Using PI as a base for the solar cell results in some additional challenges in comparison with using glass for it. On the one hand Roll-to-Roll sputter systems with a much higher degree on sophisticated mechanical components to be used instead of Inline-systems. On the other hand some features of the plastic substrate like outgassing, shrinking behaviour, skin structure and low thermal capacity require a technical and technological adjustment to figure out optimized sputter parameter. Furthermore the continuous improvement of the major components of sputter machines like targets, magnet bars and power supplies result in a need for evaluation and qualification. This paper discusses the optimization of the mentioned sputtering processes considering a variety of technical option and parameter. As a consequence of the commissioning procedure at both processes FHR Anlagenbau GmbH qualified appropriate targets in combination with sufficient power supplies to meet the expectation of the customer.
2012 AIMCAL Web Coating & Handling Conference
© FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells CIGS thin-film solar cell Example of layer stack
0.6 mm
1 µm
Front foil / Barrier / Encapsulant TCO (ZnO:Al)
0.03 µm
CdS
< 2.0 µm
Cu(In,Ga)Se2
0.5 µm
Mo Substrate foil 2012 AIMCAL Web Coating & Handling Conference
© FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells
Back contact requirements - Molybdenum CIGS on glass
Special requirements • Na diffusion capability or/ Na barrier • Pattern ability
Common requirements •Layer thickness •Conductivity •Homogeneity •Barrier function
2012 AIMCAL Web Coating & Handling Conference
CIGS on flexible web material Special requirements • Low stress – avoid wrinkles • Bendability • Adhesion on organic foil • Pattern ability if needed © FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells Magnetron sputtering Specific resistivity Mo @800nm on PI foil for different machines/ setups consistent 2.5E-07
Ohm*m
2.0E-07 1.5E-07 1.0E-07 5.0E-08 0.0E+00 0
50
100
150 Temperature /°C
spec. Resistivity for various process pressures
200
optimized, low stress
250
300
300nm on glass
2012 AIMCAL Web Coating & Handling Conference
© FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells Magnetron sputtering of Molybdenum Layer stress, adhesion and pattern ability vs. process pressure
Laser patterning quality a.u.
•Adhesion pass/ fail
•Proc. of the 24th IEEE Photovoltaic Specialists Conference (IEEE, New York, 1995), pp. 164-167. •SODIUM DIFFUSION, SELENIZATION, AND MICROSTRUCTURAL EFFECTS ASSOCIATED WITH VARIOUS MOLYBDENUM BACK CONTACT LAYERS FOR •CIS-BASED SOLAR CELLS •John H. Scofield; Physics Department, Oberlin College, Oberlin, OH 44074 and S. Asher, D. Albin, J. Tuttle, M. Contreras, D. Niles, R. Reedy, A. Tennant, and R. Noufi •National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401
2012 AIMCAL Web Coating & Handling Conference
Process pressure
© FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells
Front contact requirements CIGS on glass
Special requirements •Pattern ability
Common requirements •Layer thickness •Conductivity •Optical properties •Homogeneity
2012 AIMCAL Web Coating & Handling Conference
CIGS on flexible web material Special requirements • Low stress • Bendability • (Pattern ability if needed) © FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells
TCO raw target material dependencies @ 200°C in production system
Raw material supplier
#1
#2
#3
Transmission n-ZnO:Al2O3; 2%wt AM1.5 weighted
89,8..90,0
89,4..89,5
89,9..90,1
Transmission i-ZnO:Al2O3; 1%wt AM1.5 weighted
87,7
88,3..88,4
-------------
Arcing behavior
good
good
fair
Different target raw materials from different suppliers are suitable for different TCO-processes
2012 AIMCAL Web Coating & Handling Conference
© FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells TCO raw target material dependencies @ 200°C Average transmission vs. specific resistivity for conductive ZnO:Al2O3
Transmission (average) %
95 90 85 Target raw material supplier 1 80 Target raw material supplier 2 75 70 65 60 400.0
500.0
600.0
700.0
800.0
900.0
1000.0
Specific resistivity / µOhm * cm 2012 AIMCAL Web Coating & Handling Conference
© FHR Anlagenbau GmbH
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Front And Back Contacts For Flexible CIGS Solar Cells
Conclusion Requirements for processes on foils are different compared to rigid substrate Each layer needs different optimization for roll to roll processing Target material plays important roll in process optimization Behavior of target material from different suppliers is different Each process ,e.g. n-ZnO vs. i-ZnO can be optimized with different target material from different suppliers to achieve the best performance for each layer
2012 AIMCAL Web Coating & Handling Conference
© FHR Anlagenbau GmbH
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