Defect characterization of polycrystalline silicon layers obtained by aluminum-induced crystallization and epitaxy

Abstract

AbstractTo reduce the harmful influence of grain boundaries in polycrystalline Si layers we make absorber layers on foreign substrates with columnar grains with a grain width larger than the grain thickness. Such layers with a grain size in the range of ~1-100 µm can be obtained by aluminum-induced crystallization and epitaxy. Until now however, the open-circuit voltage of solar cells made from such layers was quasi-independent of the grain size. To understand this fact, defect etching and Electron Backscattered diffraction (EBSD) measurements were performed to investigate the crystallographic defects. A very large density (~ 109 cm-2) of intra-grain defects (IGD) was found. Room temperature Electron Beam Induced Current (EBIC) measurements were done to localize and investigate the electrically active defects. The intra-grain defects found with defect etching showed a strong recombination activity. These results indicate that the unexpected quasi-independence on the grain size of the open-circuit voltage of our pc-Si solar cells is due to the presence of numerous electrically active intra-grain defects.