Implications of gas-barrier properties in realizing the self-recovery of photodegraded CsPbBr₃perovskite nanocrystals

Fluorescent CsPbBr₃perovskite nanocrystals (NCs) degraded by photoinduced desorption of surface ligands can exhibit self-recovery; however, irreversible oxidative damage from oxygen in the atmosphere must be avoided. In this work, gas-barrier polymer films made of ethylene vinyl alcohol (EVOH) and ethylene vinyl acetate (EVA) copolymers were investigated as sealing materials for CsPbBr₃NC films. The NC film covered with EVOH showed photodegradation with blackening and photoluminescence quenching under light excitation, while self-recovery of the optical properties was observed during dark storage. These phenomena were attributed to the photoinduced desorption of surface ligands (and thus the formation of surface defects) and their re-adsorption, respectively. In contrast, self-recovery did not occur when an EVA film was used. X-ray photoelectron spectroscopy indicated the formation of Pb-O bonds for the EVA-coated film. Thus, EVOH, which has a lower oxygen permeability than EVA, successfully prevented irreversible damage by permeated oxygen. This is an important finding for the reuse or lifetime-extension of CsPbBr₃NCs.