Fabrication of stable, large-area, thin-film CdTe photovoltaic modules. Annual subcontract report, 10 May 1991--9 May 1992

Abstract

Solar Cells, Inc (SCI) has a program to produce 60 cm X 120 cm solar modules based on CdTe films. The method of choice for semiconductor deposition is condensation from high temperature vapor`s. Early work focussed on Close Spaced Sublimation and Chemical Vapor Deposition using elemental sources, but later equipment designs no longer strictly conform to either category. Small area efficiency has been confirmed by NREL at 9.3% on a 0.22 cm{sup 2} device (825 mV Voc, 18.2 mA/cm{sup 2} Jsc, and 0.62 FF) deposited on a 100 cm{sup 2} substrate. On 8 cell, 64 cm{sup 2} submodules, the best result to date is 7.3% (5.9 V Voc, 130 mA Isc, and 0.61 FF). CdS, CdTe, and ZnTe films have been deposited onto 60 cm X 120 cm substrates - single cells produced from this material have exceeded 8% efficiency, 64 cm{sup 2} submodules have exceeded 5%. Module efficiency is limited by mechanical defects - mostly shunts - associated with processing after deposition of the semiconductor layer`s. Present best result is 1.4% total area efficiency. In anticipation of more advanced designs, CdTe films have also been deposited from apparatus employing elemental sources. This project is in an early stage and has produced only rudimentary results. A pro-active Safety, Health, Environmental and Disposal program has been developed. Results to date indicate that both employees and the environment have been protected against overexposure to hazards including toxic chemicals.