Piezoelectric Photothermal Study of the Optical Absorption Spectra of Microcrystalline Silicon

Abstract

The piezoelectric photothermal (PPT) signals from hydrogenated microcrystalline silicon (µc-Si:H) films were measured and the effects of the deposition rate on the optical properties were investigated. Increasing the deposition rate resulted in (i) a decrease in optical absorption coefficient, (ii) a shift in effective energy gap to the higher photon energy side, and (iii) a increase in the density of localized states originating from a structural disorder. These results led to a reduction in the photovoltaic conversion efficiency of the solar cells for high-deposition-rate samples. The usefulness of the PPT method for investigating the optical properties of thin and transparent µc-Si:H films was also demonstrated.