Constructing Efficient Hole-Transporting Materials by Tuning Fluorine Substitution for Inverted Perovskite Solar Cells with Efficiency Exceeding 20%

Three pyrrolo[3,2-b]pyrrole (PP) core building block-based dopant-free hole-transporting materials (HTMs) with different fluorine substitutions are synthesized and applied in inverted perovskite solar cells (PSCs). The number and the position of fluorine substitutions display a significant effect on the photochemical and photovoltaic performances of the resulting HTMs. The hexafluorine-substituted HTM 6FPPY shows excellent hole extraction efficiency and achieves a prominent power conversion efficiency (PCE) of 20.1% with negligible hysteresis and good long-term stability. This work provides an avenue for the design of low-cost, dopant-free HTMs for high-performance inverted PSCs.