Microcrystalline silicon-germanium thin films prepared by the chemical transport process using hydrogen radicals

摘要

We propose microcrystalline silicon-germanium (mu c-SiGe) as a bottom cell material of triple-junction solar cells in order to improve the conversion efficiency of thin film solar cells. The mu c-SiGe thin films were prepared by the chemical transport process using Si and Ge targets exposed to hydrogen radicals. We successfully produced highly photosensitive mu c-SiGe films with relatively low Ge composition by increasing the gas pressure, and observed the photovoltaic effect in pin solar cell structures. However, it was difficult to produce mu c-SiGe films with higher Ge composition. We found that a small amount of argon introduction into the chemical transport process enables us to increase Ge composition at the high pressure. Moreover, the argon introduction seems effective to maintain the electrical properties in relatively high Ge composition. The results suggest that the mu c-SiGe thin films prepared by the chemical transport process are one of the candidates for new photovoltaic materials.