Bulk heterojunction perovskite hybrid solar cells with large fill factor

A major limitation to increasing the efficiency of perovskite hybrid solar cells (pero-HSCs) is the fact that the diffusion length of the electrons is shorter than that of the holes. To facilitate the electron extraction efficiency in pero-HSCs and to make this efficiency comparable with that of the holes, we fabricated bulk heterojunction (BHJ) pero-HSCs by mixing perovskite materials with water-/alcohol-soluble fullerene derivatives. The observed enhanced short-circuit current densities (JSC) and enlarged fill factors (FF) were a result of the balance in the charge carrier extraction efficiency and the enlarged interfacial area between the perovskite materials and the fullerene derivatives. Significantly improved power conversion efficiencies were obtained for these BHJ pero-HSCs. A greater than 22% increase in power conversion efficiency was observed for the BHJ pero-HSCs compared with planar heterojunction pero-HSCs. A remarkable 86.7% FF, the highest reported value for pero-HSCs, was observed for the BHJ pero-HSCs. Our strategy of using a BHJ structure in pero-HSCs offers an efficient and simple way to further increase the performance of these devices.