An assessment of the suitability of rf sputtered amorphous hydrogenated Si as a potential solar cell material

Abstract

We review several material properties thought to be important for the production of high efficiency amorphous semi-conductor Schottky barrier solar cells, with particular reference to a systematic study made in this laboratory of amorphous Si:H alloys prepared by rf sputtering. These requirements include: (a) an optical gap which efficiently absorbs the solar spectrum in a thin film, (b) a Fermi level position close to the conduction band for a large work function difference between metal and semiconductor, (c) high photoconductivity, (d) long carrier migration lengths, and (e) a low overall density of gap states. Using our data on these electronic properties, we show that we can satisfy these conditions somewhat by depositing at an argon pressure of 20 mTorr. Furthermore, we demonstrate, using a simple Schottky barrier structure, that significant improvements in device performance are achieved, particularly in open circuit voltage, as the above properties are optimized. Other factors which might still limit the performance of the device are discussed, and from an examination of the temperature dependence of the short circuit current, we conclude that the most likely to be important is the "effective" diffusion length for valence band holes. © 1980 AIME.