Pure Chloride 2D/3D Heterostructure Passivation for Efficient and Stable Perovskite Solar Cells

To date, organic–inorganic hybrid perovskite solar cells (PSCs) have reached a certified efficiency of 25.7%, showing their great potential in industrial commercialization. However, defects at the surface and grain boundaries hinder their device performance and long‐term stability. Herein, long‐chain dodecylammonium halides (DACl, DABr, and DAI) to treat the perovskite surface and improve the device performance are introduced. It is found that the three passivators can all form 2D perovskites but with different halide compositions. The DACl‐treated perovskite forms a pure chloride DA 2 PbCl 4 2D perovskite, while the DABr and DAI‐treated surfaces form a pure iodide DA 2 PbI 4 2D perovskite. Compared with the DA 2 PbI 4 layer, it is found that the DA 2 PbCl 4 passivation layer can more effectively passivate defects, improve carrier separation at the perovskite surface, and optimize the energy alignment between the perovskite film and hole transport layer. As a result, a champion power conversion efficiency of 23.91% is achieved for the DACl‐treated PSCs. Moreover, the device maintains around 95% of its initial efficiency after 1000 h storage under relative humidity of 10% at 25 °C.