High‐Efficiency Perovskite Solar Cells with Imidazolium‐Based Ionic Liquid for Surface Passivation and Charge Transport

Abstract Surface defects have been a key constraint for perovskite photovoltaics. Herein, 1,3‐dimethyl‐3‐imidazolium hexafluorophosphate (DMIMPF 6 ) ionic liquid (IL) is adopted to passivate the surface of a formamidinium‐cesium lead iodide perovskite (Cs 0.08 FA 0.92 PbI 3 ) and also reduce the energy barrier between the perovskite and hole transport layer. Theoretical simulations and experimental results demonstrate that Pb‐cluster and Pb‐I antisite defects can be effectively passivated by [DMIM] + bonding with the Pb 2+ ion on the perovskite surface, leading to significantly suppressed non‐radiative recombination. As a result, the solar cell efficiency was increased to 23.25 % from 21.09 %. Meanwhile, the DMIMPF 6 ‐treated perovskite device demonstrated long‐term stability because the hydrophobic DMIMPF 6 layer blocked moisture permeation.