Asymmetrical benzothiadiazole core-based hole transport materials for planar perovskite solar cell

For the purpose of fabricating high performance hole transport materials (HTMs) for n-i-p planar perovskite solar cells (PSCs), two asymmetric and one symmetric structured donor-acceptor-donor (D-A-D) type small molecules (a-BTC, a-BTBC and BTDC) were synthesized by introducing two different peripheral groups toward benzothiadiazole core. The a-BTBC with longer π conjugation lengths shows good film formation property, higher hole mobility and conductivity, and achieves power conversion efficiency (PCE) of 23.5 %. It can retain 80 % of the initial PCE after aging 30 days in an ambient condition with relative humidity of 40–60 %. Our results show the potential and provides reference for molecular design of asymmetric structured HTMs.