Dual-Interface Passivation Strategy using Imidazolium Ionic Liquid for High-Performance CsPbI2Br Perovskite Photovoltaics

Abstract

Interfacial defects at the junction between CsPbI₂Br perovskite layer and the electron transport layer triggered significant nonradiative recombination and charge carrier loss, severely compromising the efficiency and stability of CsPbI₂Br 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 SnO₂ surface and buried CsPbI₂Br interface. Systematic characterizations revealed that TMBr synergistically enhances charge transport dynamics through two distinct mechanisms: 1) suppression of under-coordinated Sn⁴⁺ cations and oxygen vacancies (V_O) at the SnO₂ 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 CsPbI₂Br 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.