Aromatic 2,2-Diphenylethylamine Ligand Exchange of FACsPbBr Perovskite Nanocrystals for High-Efficiency Pure Green Light-Emitting Diodes.

Perovskite nanocrystals (NCs) with long alkyl ligands cannot easily form high-quality composite films owing to their poor dispersibility in π-conjugated small molecules and polymer host materials. In this study, we demonstrated that the aromatic ligand exchange of mixed-cation FACsPbBr NCs using 2,2-diphenylethylamine (DPEA) can not only enable the fabrication of high-efficiency light-emitting diodes (LEDs) but also allows dispersibility in host materials. The DPEA-NC film exhibited a pure green wavelength of 530 nm and a full width at half-maximum of 20.9 nm with a photoluminescence quantum yield of 90.9%. A DPEA-NC LED achieved a luminance of 39,700 cd/m and an external quantum efficiency of 18.6% even in a thick NC film. Interestingly, the DPEA-NCs formed a composite film with small-molecule tris(4-carbazoyl-9-ylphenyl)amine. The operational stability of this composite LED was eight times higher than that of the DPEA-NC LED owing to enhanced hole-electron charge balance and the suppression of perovskite NC degradation. Therefore, the aromatic DPEA ligand exchange of perovskite NCs is an effective way to improve their electrical properties and operational device stabilities.