文摘
It has been shown that in hybrid polymer鈥搃norganic photovoltaic devices not all the photogenerated excitons dissociate at the interface immediately, but can instead exist temporarily as bound charge pairs (BCPs). Many of these BCPs do not contribute to the photocurrent, as their long lifetime as a bound species promotes various charge carrier recombination channels. Fast and efficient dissociation of BCPs is therefore considered a key challenge in improving the performance of polymer鈥搃norganic cells. Here we investigate the influence of an inorganic energy cascading Nb<sub>2sub>O<sub>5sub> interlayer on the charge carrier recombination channels in poly(3-hexylthiophene-2,5-diyl) (P3HT)鈥揟iO<sub>2sub> and PbSe colloidal quantum dot鈥揟iO<sub>2sub> photovoltaic devices. We demonstrate that the additional Nb<sub>2sub>O<sub>5sub> film leads to a suppression of BCP formation at the heterojunction of the P3HT cells and also a reduction in the nongeminate recombination mechanisms in both types of cells. Furthermore, we provide evidence that the reduction in nongeminate recombination in the P3HT鈥揟iO<sub>2sub> devices is due in part to the passivation of deep midgap trap states in the TiO<sub>2sub>, which prevents trap-assisted Shockley鈥揜ead鈥揌all recombination. Consequently a significant increase in both the open-circuit voltage and the short-circuit current was achieved, in particular for P3HT-based solar cells, where the power conversion efficiency increased by 39%.
