Amorphous-silicon solar cells. Final report, 1 October 1980-31 December 1981

An analysis of the transport in p-i-n cells indicates that back diffusion of carriers can account for approximately half of the observed losses in the collection efficiency at short wavelengths. Auger electron spectroscopy has been used to show that a-Si:H films become continuous after 40 to 50 A of growth. High conductivity films have been produced in both dc and rf discharges and consist of a mixture of microcrystalline and amorphous phases in both cases. The surface photovoltage method has been used to measure hole diffusion lengths in undoped a-Si:H as large as 1.1 ..mu..m (while exposed to 0.1-AMl illumination). The Hall mobility in p-type a-Si:H films can exhibit either a positive or negative sign depending on boron doping level and measurement temperature; values as large as 0.2 cm/sup 2/V/sup -1/s/sup -1/ have been observed at room temperature. We have fabricated p-i-n solar cells using microcrystalline p-layers, and these cells have exhibited conversion efficiencies as high as 6.6% and open-circuit voltages as high as 920 mV. With a-(Si,C):H p layers, open-circuit voltages as large as 933 mV have been observed. Photovoltage profiling of p-i-n cells has shown that most of the open-circuit voltage is generated by the p/i interface andmore » that unstable cells possess a zero-field region near the center of the i layer. Contact studies have shown that the contribution of the TCO/p interface to the series resistance is usually negligible, but the n/Ti-Al interface may contribute 1 to 10 ..cap omega.. cm/sup 2/.« less