Chemical Vapor Deposition of Thin-Film Polycrystalline Si for Low-Cost Solar Cells. Third Quarterly Technical Progress Report, February 2, 1980-May 2, 1980

摘要

The program has emphasized a study of the transport properties of p-type polycrystalline Si films as functions of average grain size and impurity doping concentration. Preliminary investigations of nucleation and early-stage growth phenomena in such films have also been carried out to provide improved understanding of the fundamental properties of the films that limit photovoltaic performance and thus to establish a good technical basis for subsequent attempts to achieve improved performance in solar cells using such films. Also, the study of transport properties was extended to n-type polycrystalline Si films. The transport studies have involved preparation of sets of B-doped p-type and P-doped n-type polycrystalline films grown simultaneously by SiH sub 4 pyrolysis in H sub 2 on polycrystalline high-purity alumina substrates in a range of average grain sizes (approx. 1 mu m to approx. 125 mu m) and with a range of impurity doping concentrations from approx. 10 exp 15 to >10 exp 20 cm exp -3 , primarily at approx. 985 exp 0 C. The p-type films have been characterized in detail by measurements of transport properties of a function of sample temperature in the range 77 to 420 exp 0 K. The results of these investigations are described in detail. In particular, the height of the intergrain barrier in polycrystalline Si as a function of doping concentration as well as average grain size has been determined, and comparisons of these experimental results with the predictions of the grain-boundary trapping model for conduction in polycrystalline Si are made. Sets of CVD polycrystalline and single-crystal films have been used for the fabrication of solar cells, utilizing both vapor-grown and P-diffused junctions. The experimental solar cell structures have had generally poor photovoltaic properties, in most instances for easily diagnosed reasons. (ERA citation 06:008768)