Hole transporting materials (HTMs) play a critical role in ameliorating the performance of perovskite solar cells (PSCs). Dedicated HTMs can improve not only the hole extraction and efficiency but also the stability. Herein, PFDT-COOH and its fluorinated derivative, PFDT-2F-COOH, are introduced as dopant-free HTMs for inverted PSCs. Compared to PFDT-COOH, PFDT-2F-COOH exhibits a deeper highest occupied molecular orbital (HOMO) level, a higher work function on indium tin oxide electrodes, and an elevated built-in potential in the device. The PFDT-COOH device based on FA_1−xMA_xPbI₃ mixed-cation perovskite exhibits a champion power conversion efficiency (PCE) of 20.64%, while the PFDT-2F-COOH device exhibits a champion PCE of 21.68%, which is close to the highest value (21.7%) attained in inverted single-junction PSCs. The elevated efficiency is attributed to reduction of carrier recombination and enhancement of carrier extraction via the fluorination strategy. In addition, the two devices also show excellent operational and thermal stabilities. Therefore, our work offers a feasible strategy for preparing high efficiency and stable inverted PSCs.

中文翻译：

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通过氟化不含掺杂剂的空穴传输材料，在倒钙钛矿太阳能电池中实现超过21％的效率

空穴传输材料（HTM）在改善钙钛矿太阳能电池（PSC）的性能中起关键作用。专用HTM不仅可以改善孔的提取和效率，还可以提高稳定性。此处，PFDT-COOH及其氟化衍生物PFDT-2F-COOH作为反向PSC的无掺杂HTM引入。与PFDT-COOH相比，PFDT-2F-COOH表现出更深的最高占据分子轨道（HOMO）水平，在铟锡氧化物电极上的更高的功函以及更高的内置电势。基于FA _{1- x} MA _x PbI ₃的PFDT-COOH设备混合阳离子钙钛矿的最佳功率转换效率（PCE）为20.64％，而PFDT-2F-COOH器件的最佳功率转换效率为21.68％，接近于反向单结所达到的最高值（21.7％）。 PSC。效率的提高归因于载流子重组的减少和通过氟化策略的载流子提取的增强。此外，这两种器件还具有出色的操作和热稳定性。因此，我们的工作为制备高效，稳定的反相PSC提供了可行的策略。