The origin of the difference in the optimum processing temperature of microcrystalline Si (µc-Si:H) solar cells depending on the device structure was studied. The 2 different types of structure were compared with each other. They were a superstrate-type cell, and a substrate-type cell in which the order of the deposited layer was p-i-n and n-i-p on the substrate. Some µc-Si:H solar cells at various deposition temperatures of the i layer were fabricated under contamination-free conditions by using an ultra-high vacuum system. It was found that the optimum temperature for the superstrate-type cell was lower than that for the substrate-type cell and that a significant degradation of the cell performance occurred during the deposition of the i layer at higher temperatures. The degradation was attributed to the formation of the defect at the p/i interface due to the enhanced diffusion of the B from the underlying layer to the intrinsic layer. It was also found that this degradation and the enhanced diffusion do not take place for P or post-deposition annealing. It was speculated that the enhanced B diffusion was mediated by the Si-Si bond breaking and its accompanying structural relaxation caused by atomic H.

Formation of Interface Defects by Enhanced Impurity Diffusion in Microcrystalline Silicon Solar Cells. Y.Nasuno, M.Kondo, A.Matsuda, H.Fukuhori, Y.Kanemitsu: Applied Physics Letters, 2002, 81[17], 3155-7