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

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.