Separating Crystal Growth from Nucleation Enables the in-situ-controllable Synthesis of Nanocrystals for Efficient Perovskite Light-emitting Diodes.

Colloidal perovskite nanocrystals (PNCs) display bright luminescence for light-emitting diode (LED) applications; however, they require post-synthesis ligand exchange that may cause surface degradation and defect formation. In-situ-formed PNCs achieve improved surface passivation using a straightforward synthetic approach, but their LED performance in the green wavelength is not yet comparable with that of colloidal PNC devices. Here we find that the limitations of in-situ-formed PNCs stem from uncontrolled formation kinetics: conventional surface ligands confine perovskite nuclei but fail to delay crystal growth. We introduce a bifunctional carboxylic-acid-containing ammonium hydrobromide ligand that separates crystal growth from nucleation, leading to the formation of quantum-confined PNC solids exhibiting a narrow size distribution. Controlled crystallization is further coupled with defect passivation using deprotonated phosphinates, enabling improvements in photoluminescence quantum yield to near unity. We fabricate green LEDs with a maximum current efficiency of 109 cd A -1 and average external quantum efficiency of 22.5% across 25 devices - exceeding the performance of colloidal PNC-based counterparts; We further document a 45.6-hour operating half-time for an unencapsulated device in N 2 with an initial brightness of 100 cd m -2 . This article is protected by copyright. All rights reserved.