Hole‐Transporting Polymers Bearing Fine‐Tuning Side Chains via Ternary Copolymerization Strategy for High‐Performance Perovskite Solar Cells

Abstract The binary electron donor–electron acceptor (D‐A) type conjugated polymers have proven to be efficient dopant‐free hole‐transporting materials (HTMs) for the n‐i‐p perovskite solar cells (PVSCs). However, D‐A type terpolymeric HTMs containing two D units are not exploited. Reserving the high‐planarity backbone of benzodithiophene (BDT)‐benzodithiophene‐4,8‐dione, D 1 ‐A‐D 2 ‐A type terpolymers PT‐Cz30, PT‐Cz50, and PT‐Cz70 are obtained by side‐chain engineering and ternary copolymerization strategy, in which BDT bearing the side chains of thiophene and carbazole serves as D 1 and D 2 units, respectively. PT‐Cz50 performs best due to the appropriate side‐chain ratio around 1:1. Meanwhile, a polymer blend HTM PA‐Cz50 is studied for comparison, in which two binary D‐A polymers PBDB‐T and PBDB‐Cz are blended with the molar ratio of 1:1. Containing similar side‐chain composition, terpolymer PT‐Cz50 presents superior hole transport properties over the polymer blend PA‐Cz50 and endows better device performances to the PVSCs with a promising power conversion efficiency of 22.53% and high device stability.