What parameters can be reliably deduced from the current-voltage characteristics of an organic bulk-heterojunction solar cell?

Abstract

Through the analysis of scales and simplification of the drift-diffusion device model, we have obtained a quantitative description of the mechanisms underlying the current-voltage (j–V) characteristics of organic bulk-heterojunction solar cells. The mechanisms have been resolved into the competition between the photogeneration, recombination, and extraction/injection rates, which determines the bulk charge carrier concentration; and the combined effect of the built-in field and the boundary layers in shaping the electric potential distribution, which determines the bulk field. The relationships between the j–V characteristics and standard model parameters have been captured with analytical expressions and verified through 1-D numerical simulations. We have determined that while the charge carrier generation rate can be reliably extracted with the device model from j–V measurements alone, the effective density of states and built-in potential, and the mobility and recombination prefactor are clustered pairs that can only be decoupled through other characterization techniques.