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.