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Thin microcrystalline silicon-germanium films (μ-Sil.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 μ-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 pc-Sil-xGex:H i-layers have been prepared for the first time. An efficiency of η = 3.1 % under AM1.5 has been obtained for a cell with 150 nm thin i-layer.

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Profiled buffer layers at the interfaces of amorphous silicon–germanium (a-SiGe:H) solar cells are routinely used to avoid band-gap discontinuities and high-defect densities at the p/i and i/n interfaces. It is shown that such profiled a-SiGe:H buffer layers can be replaced by a constant band-gap a-Si:H buffer, an inverse profiled a-SiGe:H buffer, or even a 3-nm-thin (δ) buffer at some distance away from the interface without losses in the open-circuit voltage VOC and fill factor while maintaining the same short current density jSC. In view of these results, common model assumptions for a-SiGe:H solar cells have to be revised.

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