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Interface Reactions in CdTe Solar Cell Processing

Published online by Cambridge University Press:  10 February 2011

D. Albin ,
R. Dhere ,
A. Swartzlander-Guest ,
D. Rose ,
X. Li ,
D. Levi ,
D. Niles ,
H. Moutinho ,
R. Matson  and
P. Sheldon
D. Albin
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
R. Dhere
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
A. Swartzlander-Guest
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
D. Rose
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
X. Li
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
D. Levi
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
D. Niles
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
H. Moutinho
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
R. Matson
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
P. Sheldon
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
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Abstract

Currently, the best performing CdS/CdTe solar cells use a superstrate structure in which CdTe is deposited on a heated CdS/SnO2/Glass substrate. In the close-spaced-sublimation (CSS) process, substrate temperatures in the range 550°C to 620°C are common. Understanding how these high processing temperatures impact reactions at the CdS/CdTe interface in addition to reactions between previously deposited layers is critical. At the SnO2/CdS interface we have determined that SnO2 can be susceptible to reduction, particularly in H2 ambients. Room-temperature sputtered SnO2 shows the most susceptibility. In contrast, higher growth temperature chemical vapor deposited (CVD) SnO2 appears to be much more stable. Elimination of unstable SnO2 layers, and the substitution of thermal treatments for H2 anneals has produced total-area solar conversion efficiencies of 13.6% using non-optimized SnO2 substrates and chemical-bath deposited (CBD) CdS. Alloying and interdiffusion at the CdS/CdTe interface was studied using a new lift-off approach which allows enhanced compositional and structural analysis at the interface. Small-grained CdS, grown by a low-temperature CBD process, results in more CdTe1-x.Sx alloying (x=12–13%) relative to larger-grained CdS grown by high-temperature CSS (x7sim;2–3%). Interdiffusion of S and Te at the interface, measured with lift-off samples, appears to be inversely proportional to the amount of oxygen used during the CSS CdTe deposition. Our highest efficiency to date using CSS-grown CdS is 10.7% and was accomplished by eliminating oxygen during the CdTe deposition.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 485: Symposium G – Thin Film Structures for Photovoltaics , 1997 , 215
Copyright
Copyright © Materials Research Society 1998

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