Comment on Interface state recombination in organic solar cells

In a recent paper, Street et al. [Phys. Rev. B 81, 205307 (2010)] propose first-order recombination due to interface states to be the dominant loss mechanism in organic bulk heterojunction solar cells, based on steady-state current-voltage characteristics. By applying macroscopic simulations, we found that under typical solar-cell conditions, monomolecular or bimolecular recombination cannot be inferred from the slope of the light-intensity-dependent photocurrent. In addition, we discuss the validity of calculating a mobility-lifetime product from steady-state measurements. We conclude that the experimental technique applied by Street et al. is not sufficient to unambiguously determine the loss mechanism.