Hybridization of SnO2 and an In-Situ-Oxidized Ti3C2Tx MXene Electron Transport Bilayer for High-Performance Planar Perovskite Solar Cells

Tuning the electrical conductivity of two-dimensional (2D) MXenes by modifying the termination groups and controlled oxidation offers great potential for photovoltaic applications. Here, in-situ-oxidized Ti3C2Tx (O–Ti3C2Tx) MXene was introduced to form a nanoscale heterojunction with SnO2 that was applied as an electron transport layer (ETL) in a MAPbI3 perovskite solar cell (PSC). Taking advantage of the transition from metallicity to semiconductivity during the oxidation process of Ti3C2Tx, the properties of Ti3C2Tx could be tuned to have its energy levels well matched with the perovskite. Besides, the insertion of O–Ti3C2Tx improved the electron mobility of the SnO2 ETL. Hence, the O–Ti3C2Tx/SnO2 heterojunction offered better electron extraction and reduced recombination between the ETL and the perovskite, thus rendering an increase of the power conversion efficiency (PCE) from 17.68% to 20.09% and enhancement of stability in air.