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.