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

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, D1-A-D2-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 D1 and D2 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. Ternary copolymerization strategy and side-chain engineering are employed to develop three dopant-free hole-transporting materials for perovskite solar cells. Terpolymer PT-Cz50 bearing the optimal side-chain ratio of thiophene and carbazole also surpass its polymer blend counterpart PA-Cz50, due to the superior molecular aggregation and stacking pattern, and endows the devices a champion power conversion efficiency of 22.53% and high stability.image