High‐Efficiency Carbon‐based CsPbI₂Br Perovskite Solar Cells from Dual Direction Thermal Diffusion Treatment with Cadmium Halides

Abstract In recent years, carbon‐based CsPbI₂Br perovskite solar cells (PSCs) have attracted more attention due to their low cost and good stability. However, the power conversion efficiency (PCE) of carbon‐based CsPbI₂Br PSCs is still no more than 16%, because of the defects in CsPbI₂Br or at the interface with the electron transport layer (ETL), as well as the energy level mismatch, which lead to the loss of energy, thus limiting PCE values. Herein, a series of cadmium halides are introduced, including CdCl₂, CdBr₂ and CdI₂ for dual direction thermal diffusion treatment. Some Cd²⁺ ions thermally diffuse downward to passivate the defects inside or on the surface of SnO₂ ETL. Meanwhile, the energy level structure of SnO₂ ETL is adjusted, which is in favor of the transfer of electron carriers and blocking holes. On the other hand, part of Cd²⁺ and Cl⁻ ions thermally diffuse upward into the CsPbI₂Br lattice to passivate crystal defects. Through dual direction thermal diffusion treatment by CdCl₂, CdI₂ and CdBr₂, the performance of devices has been significantly improved, and their PCE has been increased from 13.01% of the original device to 14.47%, 14.31%, and 13.46%, respectively. According to existing reports, 14.47% is one of the highest PCE of carbon‐based CsPbI₂Br PSCs with SnO₂ ETLs.