Microcrystalline SiGe Absorber Layers in Thin-film Silicon Solar Cells

We report on physical properties of microcrystalline silicon-germanium (μc-SiGe:H) absorber layers for the use as a bottom structure in silicon based multijunction thin-film solar cells. Due to incorporation of Ge the absorption of the film is enhanced compared to pure μc-Si:H films. This provides the opportunity to significantly reduce the absorber layer thickness. The experiments were carried out in a 13.56 MHz PECVD reactor using germane, silane and hydrogen as process gases. Single layers were characterized for their optical and electrical properties. Results from single and multijunction solar cells using a μc- SiGe:H absorbers will be shown. In tandem solar cells a reduction of about 60% of the absorber layer thickness could be reached by using SiGe alloys compared to pristine silicon tandem cells.