Two Birds with One Stone: Defect Passivation and Energy Level Optimization Achieved by Using Ionic Liquid Additives for Printable Mesoscopic Perovskite Solar Cells with Efficiency beyond 16%

Printable mesoscopic perovskite solar cells (p-MPSCs) have received extensive attention from researchers and entrepreneurs worldwide because of their low cost, simple manufacturing process, and feasible fabricate in air. However, the wide application of p-MPSCs is limited by their relatively low power conversion efficiency (PCE). Herein, we propose a performance enhancement strategy for p-MPSCs by introducing 1-benzyl-3-methylimidazolium chloride (BZMIMCl) ionic liquid into a perovskite precursor. The BZMIMCl ionic liquid optimized the crystallization of perovskite films, modulated the energy band alignment of the perovskite, and improved carrier transport, thereby enhancing the overall photovoltaic parameters and stability of p-MPSCs. The champion PCE of the BZMIMCl-optimized device was 16.06%. Moreover, the unencapsulated p-MPSCs containing BZMIMCl maintained ∼89.6% of its maximum value after being stored for 60 days in an atmospheric environment (25 ± 5 °C @ 50 ± 5% RH, in the dark). This work further promotes the application of ionic liquids in the development of efficient p-MPSCs.