Impact of Blend Morphology on Interface State Recombination in Bulk Heterojunction Organic Solar Cells

International audienceThis work is a re-investigation of the impact of blend morphology and thermal annealing on the electrical performance of regioregular P3HT:PC 60 BM. The blend is first characterized by combining atomic force microscopy, X-rays diffraction and Time-of-Flight experiments. Then, current-voltage characteristics of photodiode devices are measured in the dark and under illumination. Finally, the existence of exponential tails of electronic gap states is experimentally confirmed by measuring the device spectral response in the sub-band gap regime. This method reveals the existence of a large density of gap states, which is partially reduced by successive annealing steps. The comparison between drift and diffusion 2 simulations and charge transport experiments show that, when band gap tails are properly taken into account, simulations can satisfactorily reproduce experimental currents under both dark and illumination conditions as a function of voltage and annealing time. This work further confirms the critical impact of tails states on the performance of solar cells