Band gap grading in microcrystalline silicon germanium thin film solar cells

In this work, hydrogenated microcrystalline silicon germanium (μc-SiGe:H) thin film solar cells with a novel band gap grading profile have been designed. By comparing different profile types (normal profile, reverse profile and no profile), the normal profile was formed in sequence by the superposition of a high Ge content layer, a Ge content grading layer and a μc-Si:H layer has been proposed. This structure exhibits higher short-circuit current density (Jsc) than conventional cell design with the similarly Ge content owing to the enhancement of the infrared response. Finally, an initial efficiency of 6.53% was achieved by μc-SiGe:H solar cell with this novel cell structure. The results have demonstrated a great potential of the μc-SiGe:H solar cells as the infrared absorber in multi-junction silicon based thin film solar cells.