Optimization of c-Si films formed by zone-melting recrystallization for thin-film solar cells

摘要

Zone-Melting Recrystallization (ZMR) is able to transform microcrystalline Si films on amorphous substrates into high quality multicrystalline films with grain size comparable to mc-Si ingot material. To reduce the costs of the process a new method to grow the necessary capping oxide directly in the ZMR system has been explored. Further the dependence of crystallographic and electrical film quality on scan speed and film thickness has been investigated. Si film quality has been evaluated by in-situ observation of the solidification front morphology, by Etch Pit Density (EPD) mappings, Modulated Free Carrier Absorption (MFCA) mappings and the preparation of test solar cells. A clear correlation between film properties and solar cell parameters was found. Hydrogen passivation is capable to improve the quality of the Si films significantly. From films grown at low scan speed up to 13.5% efficient thin-film solar cells were fabricated.