Sequentially Fluorinated PTAA Polymers for Enhancing VOC of High-Performance Perovskite Solar Cells

The energy level alignment of the perovskite and hole transporting materials (HTMs) is essential for increasing the open-circuit voltage (V-oc) and enhancing the performance of perovskite solar cells (PSCs). In this work, new sequentially fluorinated poly(triarylamine) polymers (PTAA, 1F-PTAA, and 2F-PTAA) with tuned highest occupied molecular orbital (HOMO) energy levels are developed and applied as HTMs into PSCs. The fluorination approach successfully leads to stepwise downshifting of the HOMO levels of PTAA derivatives, resulting in an obvious increase in the V-oc and power conversion efficiency (PCE) of the PSCs. In particular, introduction of 1F-PTAA polymer in (FAPbI(3))(0.85)(MAPbBr(3))(0.15)-based mesoporous n-i-p structure PSCs achieves the high stabilized PCE of 21.2% at the maximum power point with improved V-oc of 1.14 V. To elucidate the importance of the optimized degree of fluorination of PTAA polymers on the photovoltaic performances, the optical, electrical, photophysical properties, and doping behaviors of the fluorinated PTAA derivatives are investigated.