Abstract
Engineering of inorganic-organic lead halide perovskites for photovoltaic applications has experienced significant advances in recent years. However, the use of the relatively expensive spiro-OMeTAD as a hole-transporting material (HTM) poses a challenge due to dopant-induced degradation. Herein we introduce two new three-armed and four-armed HTMs (BTT-4 and BTT-5) based on isomeric forms of benzotrithiophene (BTT). The isomerism impact on the optical, electrochemical and photophysical properties and the photovoltaic performance is systematically investigated. Perovskite solar cells (PSCs) using BTT-4 and BTT-5 as HTMs show remarkable light-to-energy conversion efficiencies of 19.0% and 18.2%, respectively, under standard measurement conditions. These results validate the readily available BTT heteroaromatic structure as a valuable core for the design of highly efficient HTMs for the preparation of PSCs.