Ligands Anchoring Stabilizes Metal Halide Perovskite Nanocrystals

Instability of colloidal iodine-based inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (IPNCs) represents a major obstacle in lead-halide IPNC research and application. Herein, a ligand-anchoring process is reported that enables significantly improved colloidal stability of the iodine-based IPNCs for over 10 months in ambient. Apart from the previous efforts in searching for strong binding ligands to cap the IPNCs to incrementally reduce the exposure of the IPNC surface to the harsh colloidal environment, the ligand-anchoring method demonstrates that such an exposure can be reduced substantially by suppressing the dynamic ligand exchange around the colloidal IPNCs. In the IPNC synthesis solution with common oleic acid (OA) and oleylamine (OLA) ligands with relative weak binding to IPNCs, a systematic reduction of the ligand concentration using hexane by an order of magnitude has shown to be effective in achieving OA/OLA ligand-anchored iodine-based IPNCs with superior stability as confirmed in optical absorption, photoluminescence, H-1 solution nuclear magnetic resonance spectroscopy, and photoresponse. This result has revealed that the intermittent exposure of the IPNC surface during the dynamic ligand exchange is a primary mechanism underlying the colloidal IPNC instability, which can be resolved in the ligand-anchoring process by suppressing such dynamic activities.