Hole transport materials (HTMs) with appropriate energy levels and comprehensive passivation effects help to obtain highly efficient and stable perovskite solar cells (PSCs). Electron-deficient character-induced HTMs can generate varying energy level alignments near the HTM/perovskite interface. Herein, we report the synthesis and investigation of two new dipolar HTMs, WWC103 and WWC105, based on 2-(1,1-dicyanomethylene)rhodamine and 4-cynophenylacetonitrile acceptors, enabling high-efficiency mixed-cation mixed-halide perovskite solar cells. Apart from having different acceptors, these HTMs are built on a heterocyclic frame, which can provide passivation effects and improve the morphology of the perovskite layer. As a result, these dopant-free HTM-based solar cells show a high open-circuit voltage and good power conversion efficiency. Among both, the solar cell based on the HTM with 2-(1,1-dicyanomethylene)rhodamine exhibits a high open-circuit voltage of 1.09 V with a champion power conversion efficiency of over 20.51%. The improved performance of WWC103 over WWC105 (19.74%) is attributed to the new acceptor, which, in addition to providing good energy-level alignments and hole mobility, also holds the ability to passivate the defects. The findings suggest a new acceptor unit for constructing dopant-free HTMs for efficient PSCs.
Keywords: donor−acceptor; dopant-free hole transport materials; inverted perovskite solar cells; passivation; perovskite absorber.