Cesium-doped Ti₃C₂T_x MXene for efficient and thermally stable perovskite solar cells

Ti₃C₂T_x MXenes have been shown to be promising candidates for use in various applications. Herein, we prepare functionalized Ti₃C₂T_x MXene nanosheets doped with cesium (Cs) and introduce them into a lead iodide (PbI₂) precursor solution for perovskite solar cells (PSCs) through a two-step deposition method, combining the advantages of both additives. Our theoretical and experimental analysis reveal that cesium plays an important role in improving perovskite crystallization and thus leads to enlarged crystal grains, long-lived carrier lifetimes, and reduced charge recombination compared with the devices fabricated without and with undoped Ti₃C₂T_x MXene. PSCs integrated with cesium-doped Ti₃C₂T_x MXene deliver high photovoltaic efficiency of up to 21.57% with excellent thermal stability. The incorporation of Cs-Ti₃C₂T_x paves the way to further improve the photovoltaic performance and thermal stability of PSCs by indirectly introducing dopants.