Photocatalytic Degradation of Alkyl Halide Molecules and Anion Exchange in Dispersions of CsPbBr₃ Perovskite Nanocrystals

Since the first successful implementation of bottom-up growth of colloidal cesium lead halide perovskite nanocrystals (PNCs), these materials have generated intense interest and much activity. This has been motivated by the combination of unique photophysical properties with the ionic nature of the semiconducting cores. One interesting property of these materials is the ability to substitute the halide elements in the crystal lattice through anion exchange.<br/>Here, we present a detailed investigation of the photo-assisted anion exchange reaction of CsPbBr₃ NCs dispersed in chlorinated solvents. We probe the kinetics of this process by varying the irradiation source, time, structure of the solvent molecules and the corresponding reduction potentials. We further carry out a thorough characterization of the PNC intermediates during the irradiation period until complete anion exchange, using optical and fluorescence spectroscopy measurements, powder X-ray diffraction (PXRD) and supplement them with x-ray fluorescence spectroscopy (XRF) to track changes in the crystal structure and stoichiometry. Our findings indicate that the PNC acts as a photocatalyst promoting the degradation of solvent molecules, via a dissociative electron transfer process. The transformation requires photons with energy that exceeds the bandgap of the materials. It also generates reactive chloride ions, triggering intensity- and time-dependent anion exchange concomitant with shifting of the optical characteristics of the samples.