Dual‐Interface Passivation Strategy using Imidazolium Ionic Liquid for High‐Performance CsPbI 2 Br Perovskite Photovoltaics

Interfacial defects at the junction between CsPbI 2 Br perovskite layer and the electron transport layer triggered significant nonradiative recombination and charge carrier loss, severely compromising the efficiency and stability of CsPbI 2 Br perovskite solar cells (PSCs). Herein, the 1‐tetradecyl‐3‐methylimidazole bromide salt (TMBr) is introduced as a dual‐interface passivator to mitigate defects at both the SnO 2 surface and buried CsPbI 2 Br interface. Systematic characterizations revealed that TMBr synergistically enhances charge transport dynamics through two distinct mechanisms: 1) suppression of under‐coordinated Sn 4+ cations and oxygen vacancies ( V O ) at the SnO 2 interface, leading to improved conductivity and electron mobility; and 2) passivation of Pb‐I antisite defects and undercoordinated halide ions (Br − /I − ) within the buried perovskite interface, enabling the formation of high‐quality CsPbI 2 Br films. Consequently, the TMBr‐modified device achieved a remarkable open‐circuit voltage ( V OC ) of 1.324 V, and thus, associated with a high PCE of 17.27%, along with long‐term stability, retaining 95.5% of its initial PCE after 720 h under ambient conditions (∼25°C and ∼25% RH), underscoring the critical role of interfacial defect management in advancing PSC performance.