How does changing substituents affect the hole transport characteristic of butterfly-shaped materials based on fluorene–dithiophene core for perovskite photovoltaics

Abstract

Ten butterfly-shaped compounds based on fluorene–dithiophene (FDT) core containing para-substituted N,N-phenylamine moieties were designed as hole transporting materials (HTMs) for perovskite solar cells (PSCs). Among different HTMs, only HOMO level of NO2 containing molecule was placed lower than the that of CH3NH3PbI3 (MAPbI3) perovskite which confirmed all materials but the NO2 substituted compound could efficiently inject holes from the MAPbI3 towards the Au cathode electrode. Also, the LUMO levels of all HTMs indicated higher energies compared to that of MAPbI3 verifying inhibited electron backward transport to the Au cathode electrode. The HTM with NMe2 substituent showed maximum hole mobility of 1.033 × 10−3 cm2V−1s−1 which was greater than those of the reference FDT-OMe HTM and Spiro-OMeTAD. The FDT-H illustrated the biggest open-circuit voltage (VOC), fill factor (FF) and power conversion efficiency (PCE) of 1.149 V, 0.895 and 23.342%, respectively, establishing it could be the best HTM candidate for high performance MAPbI3-based PSCs. The photovoltaic parameters of PSCs containing formamidinium lead iodide (FAPbI3) and FDT-core or Spiro-OMeTAD HTMs were superior to those of the MAPbI3-based solar cells.