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In this paper, we present results of collection efficiency versus wavelength measurements on thick (⩾1 μm) amorphous silicon Schottky barrier photovoltaic devices illuminated through both the ohmic and Schottky contacts. These results enable us to infer the zero-field minority carrier diffusion length in amorphous silicon-based alloys by using an appropriate theoretical model. For intrinsic a-Si:H (hydrogen) films produced by the glow discharge of silane this was found to be ∼2,100 Å. Our novel approach of illuminating the devices through the ohmic contact ensures that the collection efficiency results are extremely sensitive to the minority carrier diffusion length, and we also compare this approach to surface photovoltage type experiments which we show can lead to overestimation of this quantity.

The depletion of energy resources should produce an increase in the range of applications for terrestrial solar cells. The main factor determining the extent of this increase will be cost. In this respect, thln-film solar cells are particularly promising. Recent work on cells based on doped amorphous silicon is reviewed in detail. The properties of this relatively new material are still poorly understood. CONTENTS

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Metal-insulator-semiconductor-type photovoltaic devices using amorphous Si:F:H alloys have been fabricated. Conversion efficiencies of up to 6.3% under AM:1 illumination have been observed. These represent the highest efficiencies yet reported for amorphous thin-film solar cells.