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Research on high-efficiency, single-junction, monolithic thin-film amorphous silicon solar cells. Semiannual subcontract progress report, 1 October 1984-31 March 1985

One of several tasks of the research reported here is the study of light-induced defects in intrinsic amorphous silicon, including both photoconductivity decay and recovery kinetics. The recovery was found to be thermally activated. The interdiffusion of Al and Si across the Al/a-Si:H interface has also been studied. As far as bulk diffusion of Al and Si is concerned, the interface appears stable at solar cell operating temperatures. However, substantial out-diffusion of Si through Al grain boundaries has been detected. Computer programs have been written for optical analysis of multi-layered, thin-film cells with and without light trapping. The energy dependence of the refractive index for undoped a-Si:H and p-type a-Si/sub x/C/sub 1-x/:H has been determined from reflectance and transmittance measurements. The effect of tin oxide morphology on cell performance has also been investigated. Granular tin oxide leads to lower open-circuit voltages but higher currents, fill factors, and efficiencies. Light soaking and annealing studies have been performed on single-junction cells, and the results suggest a reduction in carrier collection length due to excess carrier recombination. The influence of tin oxide resistivity and transmission on module design has also been investigated, and the effect of tin oxide thickness calculated.