In-Situ Interfacial Reaction Induced Amino-Rich Oxide Surface to Grow High-Quality FAPbBr3 Crystals for Efficient Inverted Light-Emitting Diodes

Iodine-based perovskite light-emitting diodes (PeLEDs) utilizing zinc oxide (ZnO) films as electron-transporting layers (ETLs) show excellent efficiency and stability. However, the poor understanding of the reaction between bromine-based perovskites and ZnO films hinders the preparation of high-quality bromine-based perovskites on ZnO films. Here, we demonstrate an in situ interfacial amidation reaction between one amino group of formamidinium bromide (FABr) and sol–gel ZnO film, leaving unreacted amino groups to form an amino-rich ZnO/perovskite interface. The density of amino groups, which can regulate the crystallization of FAPbBr3, is determined by the original carboxylate groups of the ZnO film. Carboxylate groups-rich zinc–magnesium oxide film is further developed to grow high-quality FAPbBr3 crystals. The resultant inverted PeLEDs show a low turn-on voltage of 1.8 V and a peak external quantum efficiency of 12.7%, the highest efficiency reported for green-emissive PeLEDs prepared directly on ZnO-based films. This significant discovery provides a promising route toward achieving high-performance inverted bromine-based PeLEDs on oxide ETLs.