Synchronous Elimination of Excess Photoinstable PbI2 and Interfacial Band Mismatch for Efficient and Stable Perovskite Solar Cells

Abstract Eliminating the undesired photoinstability of excess lead iodide (PbI 2 ) in the perovskite film and reducing the energy mismatch between the perovskite layer and heterogeneous interfaces are urgent issues to be addressed in the preparation of perovskite solar cells (PVSCs) by two‐step sequential deposition method. Here, the 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF 4 ) is employed to convert superfluous PbI 2 to more robust 1D EMIMPbI 3 which can withstand lattice strain, while forming an interfacial dipole layer at the SnO 2 /perovskite interface to reconfigure the interfacial energy band structure and accelerate the charge extraction. Consequently, the unencapsulated PVSCs device attains a champion efficiency of 24.28 % with one of the highest open‐circuit voltage (1.19 V). Moreover, the unencapsulated devices showcase significantly improved thermal stability, enhanced environmental stability and remarkable operational stability accompanied by 85 % of primitive efficiency retained over 1500 h at maximum power point tracking under continuous illumination.