Microcrystalline silicon-germanium alloys for absorption layers in thin film solar cells

Thin microcrystalline silicon-germanium films (mu c-Si1-xGex:H) prepared by PECVD at 95 MHz have been investigated. The optical absorption of these films increases in the infrared spectral region with increasing germanium content. In addition to the shift of the indirect gap an increase of the absorption coefficient above the band edge is observed. The material shows high crystallinity and exhibits good structural quality similar to pure mu c-Si:H films. The films are homogeneous on a macroscopic to a microscopic scale as confirmed by Raman spectroscopy and Electron Microscopy methods, p-i-n solar cells with mu c-Si1-xGex:H i-layers have been prepared for the first time. An efficiency of eta = 3.1 % under AM1.5 has been obtained for a cell with 150 nm thin i-layer.