Superoxide radical derived metal-free spiro-OMeTAD for highly stable perovskite solar cells
Linfeng Ye, Jiahao Wu, Sergio Catalán‐Gómez, Yuan Li, Riming Sun, Ruihao Chen, Zhe Liu, J. M. Ulloa, A. Hierro, Pengfei Guo, Yuanyuan Zhou, Hongqiang Wang
Abstract
Lithium salt-doped spiro-OMeTAD is widely used as a hole-transport layer (HTL) for high-efficiency n-i-p perovskite solar cells (PSCs), but unfortunately facing awkward instability for commercialization arising from the intrinsic Li+ migration and hygroscopicity. We herein demonstrate a superoxide radicals (•O2−) derived HTL of metal-free spiro-OMeTAD with remarkable capability of avoiding the conventional tedious oxidation treatment in air for highly stable PSCs. Present work explores the employing of variant-valence Eu(TFSI)2 salts that could generate •O2− for facile and adequate pre-oxidation of spiro-OMeTAD, resulting in the HTL with dramatically increased conductivity and work function. Comparing to devices adopting HTL with LiTFSI doping, the •O2−-derived spiro-OMeTAD increases the PSCs efficiency up to 25.45% and 20.76% for 0.05 cm2 active area and 6 × 6 cm2 module, respectively. State-of-art PSCs employing such metal-free HTLs are also demonstrated to show much-improved environmental stability even under harsh conditions, e.g., maintaining over 90% of their initial efficiency after 1000 h of operation at the maximum power point and after 80 light-thermal cycles under simulated low earth orbit conditions, respectively, indicating the potentials of developing metal-free spiro-OMeTAD for low-cost and shortened processing of perovskite photovoltaics. The migration and hygroscopicity of lithium salt in doped spiro-OMeTAD hampers the device efficiency of perovskite solar cells. Here, the authors employ Eu(TFSI)2 salts to generate superoxide radical for facile pre-oxidation, achieving enhanced efficiency and stability of solar cells and modules.