Bulk Heterojunction Perovskite Solar Cells Incorporated with Conjugated Polyfluorenes

Ambipolar transport characteristics of metal halide perovskites (MHPs) enable both hole and electron to be transported simultaneously in perovskite solar cells (PSCs); however, unbalanced charge transport is a fundamental limitation in boosting power conversion efficiency (PCE) of PSCs. Compared to the PSCs with either n-i-p or p-i-n device structures, bulk heterojunction (BHJ) PSCs, inspired by organic photovoltaics, are recognized as superior for balancing charge transport and maximizing interface interactions. This study reports high-performance BHJ PSCs, where the BHJ composites are composted with the n-type MHPs mixed with the p-type conjugated polyfluorenes. In the systematic studies, it is indicated that a small amount of conjugated polyfluorenes component can boost the crystallinity and grain size of the MHP thin film. Moreover, BHJ composite thin films possess boosted charge carrier mobility and a tendency of balanced charge transport and suppress both radiative and non-radiative charge carrier recombinations. Most importantly, an efficient photoinduced charge transport within the BHJ composite thin film boosts photocurrent. As a result, the PSCs based on the n-type MHPs:p-type conjugated polyfluorenes BHJ composite thin film exhibit 23.46% of PCE and boost stability. The results demonstrate a facial method to approach high-performance PSCs.