Overcoming the luminescence instability of colloidal mixed-halide perovskite quantum dots through ion motion confinement

Abstract

Colloidal lead halide perovskite quantum dots (PQDs) display great potential for flexible light-emitting applications; however, the practicability, especially for the mixed halide PQD counterparts, is restricted by color deterioration and intensity decline in photoluminescence (PL) caused by unintentional variation in stoichiometric ratios due to ion migration upon exposure to light. Herein, we present a collaborative strategy to stabilize the PL by confining ion motion in colloidal PQDs. Specifically, we modify the surface of CsPbBr_1.5I_1.5 QDs with a zwitterionic ligand, sulfobetaine-18, to retard ion migration and accelerate its entropy-driven reverse process (ion intermixing in the dark) simultaneously. Furthermore, we propose a high-repetition, pulse-width-modulation-enabled optical excitation approach, whereby the ion migration/intermixing kinetics can be finely controlled by adjusting the excitation duty cycle. Taken together, we attain unprecedentedly stable PL from the colloidal mixed halide PQD solution, displaying constant intensity and negligible wavelength shifts (less than 3 nm) during the 25-minute quasi-continuous photoexcitation.