Non-equivalent donor-acceptor polymers are particularly studied as dopant-free hole-transporting materials of perovskite solar cells (PVSCs) for the first time. Polymer F-15 with the appropriate D : A ratio over 1 : 1 presents suitable energy levels, high hole mobility, and good interface morphology, thus endowing the PVSCs a champion power conversion efficiency of 20.37 % with high device stability.

Abstract

Electron donor (D)-electron acceptor (A) type conjugated polymers present bright prospects as dopant-free hole-transporting materials (HTMs) for perovskite solar cells (PVSCs). Most of the reported D-A polymeric HTMs contain equivalent amounts of D and A units, while the appropriate excess proportion of D units could optimize the aggregation state of polymer chains and improve the hole transport properties of the polymers. Herein, a non-equivalent D-A copolymerization strategy was utilized to develop three indacenodithiophene-benzotriazole-based polymeric HTMs for PVSCs, named as F-10, F-15, and F-20, and the equivalent D-A polymer F-00 was studied in parallel. Effects of D : A ratio on the hole transport properties of these D-A type polymeric HTMs, including energy level, molecular stacking, hole mobility, and surface morphology, were investigated by theoretical simulation and test analysis. F-15 performed best due to the appropriate D : A ratio, endowing the PVSCs a champion power conversion efficiency of 20.37 % with high stability, which confirms the fine-tuning D : A ratio via non-equivalent D-A copolymerization strategy is very helpful to construct D-A type polymeric HTMs for high-performance PVSCs.