Direct Synthesis of Quaternary Alkylammonium-Capped Perovskite Nanocrystals for Efficient Blue and Green Light-Emitting Diodes.

Cesium lead halide nanocrystals (CsPbX NCs) are new inorganic light sources covering the entire visible spectral range and exhibiting near-unity efficiencies. While the last years have seen rapid progress in green and red electroluminescence from CsPbX NCs, the development of blue counterparts remained rather stagnant. Controlling the surface state of CsPbX NCs had proven to be a major factor governing the efficiency of the charge injection and for diminishing the density of traps. Although didodecyldimethylammonium halides (DDAX; X = Br, Cl) had been known to improve the luminescence of CsPbX NCs when applied postsynthetically, they had not been used as the sole long-chain ammonium ligand directly in the synthesis of these NCs. Herein we report a facile, direct synthesis of DDAX-stabilized CsPbX NCs. We then demonstrate blue and green light-emitting diodes, characterized by the electroluminescence at 463-515 nm and external quantum efficiencies of 9.80% for green, 4.96% for sky-blue, and 1.03% for deep-blue spectral regions.