Heterocyclic Functionalized Donor-Acceptor Hole-Transporting Materials for Inverted Perovskite Solar Cells

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.