Radiation hardness of AlGaAs n-i-p solar cells with higher bandgap intrinsic region
The radiation hardness of AlGaAs single-junction solar cells is investigated for various n-i-p solar cell designs. The material composition in both the n-p regions is varied between 3.5% and 16% Al-content, whereas the intrinsic region has a higher Al-content between 3.5% and 23%. The beginning-of-life and end-of-life quantum efficiency and current - voltage characteristics are discussed to establish trends as a function of material bandgap. It is found that, increasing the Al-content of AlGaAs tends to increase the radiation hardness of the solar cells up to an efficiency remaining factor of 85%. This enhancement mostly originates from an improved open circuit voltage remaining factor that is caused by a deterioration of the beginning-of-life performance as the Al-content increases. However, a degradation in photocurrent is observed for increasing Al content in the intrinsic region, which is partially due to minority carrier potential barriers at the base/intrinsic heterointerface. In general, increasing the bandgap of the intrinsic region improves radiation hardness, but the formation of potential barriers for minority carriers must be avoided. The diffusion lengths and damage coefficients are also extracted by modeling the quantum efficiency.