Homogenization and Rapid Oxidation of Spiro‐OMeTAD with Ionic Liquids for Efficient Perovskite Solar Cells

Abstract Spiro‐OMeTAD is widely recognized as the most effective hole transport layer (HTL) for n‐i‐p perovskite solar cells (PSCs), which typically requires doping with LiTFSI to overcome its low inherent conductivity. However, the doping takes a prolonged oxidation (≈24 h) in an ambient atmosphere, hindering the commercial development. Moreover, the aggregation of LiTFSI leads to poor conductivity and accelerated degradation of the HTL, which are often ignored. This study introduces the long‐chain ionic liquid 1‐octyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (OMIMTFSI) as a multifunctional additive to mitigate the aggregation of LiTFSI and promote the oxidation of Spiro‐OMeTAD simultaneously. The strong electrostatic interactions between OMIM + and LiTFSI, coupled with the dispersion effect of OMIM + in chlorobenzene, effectively hamper the aggregation of LiTFSI, beneficial for uniform doping and enhanced conductivity. The OMIM + also facilitates rapid oxidation of Spiro‐OMeTAD by attracting lone pair electrons from the triphenylamine group. As a result, the power conversion efficiency of PSCs processed in air is significantly improved from 21.48% to 24.04% with enhanced stability, maintaining over 80% of initial values after storing in air for 1360 h or under light and heat treatment for 500 h. This strategy provides valuable insights of designing lithium salt‐doped Spiro‐OMeTAD for efficient and stable PSCs.