Implementing a Two‐in‐One Defect Passivation Strategy Utilizing CsX for High‐Performance Printable Carbon‐Based Perovskite Solar Cells

Abstract In the rapidly advancing realm of perovskite solar cells, the rectification of defects has surfaced as a crucial scientific challenge. The control over defect states, especially in printable mesoscopic perovskite solar cells (p‐MPSCs), is hindered by the complexities of screen‐printing technology. Here a novel “two‐in‐one” defect passivation strategy is presented, through doping TiO₂ paste with cesium halide salts (CsX, where X = F, Cl, Br, I) to integrate all‐inorganic Cs halides, particularly CsF, into the electron transport layer in p‐MPSCs. Owing to the robust interaction between F⁻ ions and TiO₂ compared to Cs⁺ ions, and the inability of F⁻ to infiltrate the perovskite lattice, F⁻ and Cs⁺ play distinct roles starting from the buried interface of the p‐MPSCs. Specifically, F⁻ can rectify the oxygen vacancies on the TiO₂ surface, thus alleviating the residual stress at the perovskite's buried interface. Simultaneously, Cs⁺ diffuses to the top perovskite and mends the methylamine vacancies. As a result, the PCE of the optimal device, based on F‐doped TiO₂, witnesses a significant improvement from 16.18% (control) to 18.24%. The two‐in‐one strategy utilizing CsX from the buried interface can well realize the all‐inorganic defect rectification, thereby offering a promising prospect for the enhancement of p‐MPSC performance.