Deprotonation Process Modulated Compositional Transformation in ZnO-Based Red Perovskite Light-Emitting Diodes

Mixed formamidinium–cesium (FA–Cs) cation perovskite light-emitting diodes (LEDs) with ZnO as the electron transport layer exhibit excellent optoelectronic performance primarily due to the deprotonation reaction between the ZnO layer and FA⁺ cations. This reaction promotes FA–Cs ion exchange, forming high-quality mixed FA–Cs perovskites. However, the understanding of the deprotonation-driven structural transformation in mixed iodide–bromide (I–Br) perovskites remains incomplete. Here, we reveal that the interfacial deprotonation process, which can be modulated by the ZnO layer thickness, suppresses the formation of low-dimensional perovskites, decreases the FA–Cs ratio at the A site of formed three-dimensional perovskite, and reduces the defect density of its buried interface. With this approach, we achieve a mixed I–Br perovskite red LED with a peak external quantum efficiency of 11% at a high luminance of 6858 cd m^–2.