High-Rate Deposition of Intrinsic Amorphous Silicon Layers for Solar Cells Using Very High Frequency Plasma at Atmospheric Pressure

Abstract

We have investigated the electrical and optical properties of hydrogenated amorphous silicon (a-Si:H) films prepared with extremely high deposition rates using very high frequency (VHF) plasma of gas mixtures containing He, H2, and SiH4 at atmospheric pressure. VHF power is a very important deposition parameter governing the dissociation of SiH4 molecules and the structural relaxation of the film. When the deposition parameters are optimized, the optical gap of the film can be controlled by the H2/SiH4 ratio without appreciable deterioration in photoconductivity. On the basis of the results, the a-Si:H films have been applied to the intrinsic layers (i-layers) of p–i–n single-junction solar cells. An initial efficiency of 8.25% is obtained for the cell with an i-layer prepared at a very high deposition rate of 128.1 nm/s. However, the results suggest that unknown factors limiting cell performance still exist in the fabrication process of a-Si:H solar cells.