Effect of band tail states on the performance of organic solar cells

Organic solar cells (OSCs) without proper encapsulation undergo a continuous degradation when exposed to air. However an interim improvement in the performance of freshly made OSCs is often observed after they are subjected to a short exposure to air. The mechanism of such an interim performance improvement has not been fully understood yet. In this study, it is found that the band tail states in the photo active layer, formed due to the air exposure, correlated closely with the initial enhancement in the performance of OSCs. The results reveal that the longer lifetime and larger charge separation distance, caused by the presence of the band tail states, are beneficial for the charge separation and collection in OSCs. The free carriers generated from charge-exciton interaction also contribute to the increase in photocurrent.