Formation of interface defects by enhanced impurity diffusion in microcrystalline silicon solar cells

The origin of the difference in the optimum processing temperature of microcrystalline silicon (μc-Si:H) solar cells depending on the device structure has been studied. The two different type structures have been compared with each other, a superstrate-type cell, and a substrate-type cell where the order of the deposited layer is p-i-n and n-i-p, respectively on the substrate. We fabricate μc-Si:H solar cells at various deposition temperatures of the i layer under contamination-free conditions using an ultrahigh vacuum system. We found that the optimum temperature for the superstrate-type cell is lower than that for the substrate-type cell and that a significant degradation of the cell performance occurs during the deposition of the i layer at higher temperatures. We ascribed the degradation to the formation of the defect at the p/i interface due to the enhanced diffusion of the boron from the underlying layer to the intrinsic layer. We also found that this degradation and the enhanced diffusion do not take place for phosphorous or postdeposition annealing. We speculate that the enhanced boron diffusion is mediated by the SiSi bond breaking and its accompanying structural relaxation caused by atomic hydrogen. © 2002 American Institute of Physics.