Revelating mechnism of light ideality factor in organic solar cells

Abstract Light ideality factor, the slope of open-circuit voltage versus the logarithm of the illumination intensity, is a topic of continuing debate in solar cells. However, the generally accepted interpretation of the ideality factor will fail when the factor is larger than 2. This work demonstrates that the mechanism for light ideality factor is degeneracy of carriers by using the generalized Einstein coefficient in the drift-diffusion model. Moreover, this work proposes that the light ideality factor should satisfy the relation of 0:1:2:4 under different illumination conditions. This work challenges the generally accepted interpretation of the ideality factor and provides a better understanding of organic solar cells.