Degradation and failure mechanisms of a-Si:H solar cells with aluminum contacts

Low temperature (100°C-300°C) annealing effects on a-Si:H solar cells with Al contacts have been investigated. A reduction in shunt resistance upon annealing in the temperature range of 150-180°C for thirty minutes was observed indicating degradation of the cells. Visible morphological changes of the aluminum surface and the a-Si:H film underneath initiate at approximately 170°C. Thirty minute annealing at 180°C decreased the shunt resistance by a factor of 50 and the solar cells showed a considerable decrease in efficiency and fill factor. Annealing at 200°C and higher degraded the solar cells to the point that no conversion occurred. The degradation and failure mechanisms of the solar cells can be explained using a simple model involving aluminum diffusion into the silicon followed by crystallization and type conversion of the n⁺ a-Si:H due to aluminum counterdoping