Interparticle Ion Migration in Cesium Lead Mixed-Halide Perovskite Nanocrystal Superlattices

Lead mixed-halide perovskite nanocrystals offer exceptional optical properties but suffer from ionic instability and ion migration under external stimuli, challenging their integration into devices. While such effects have been well studied in individual NCs and films, their impact on nanocrystal assemblies remains less understood. Here, we investigate the effect of strong external electric fields on self-assembled CsPbBr_2.4Cl_0.6 nanocrystal superlattices. By positioning individual superlattices between micrometer-sized capacitor plates, we analyze field-induced changes in photoluminescence, elemental composition, and morphology. We observe position-dependent changes in emission energy correlated with halide ion redistribution, revealed by energy-dispersive X-ray analysis, resulting from a nonuniform electric field across the superlattice, and supported by finite-element simulations. In situ mass spectrometry detects bromide sublimation, suggesting a combination of inter- and intraparticle halide diffusion. Irreversibility of photoluminescence and morphological changes further support a field-driven reorganization. These findings reveal responses of CsPbBr_2.4Cl_0.6 superlattices subject to external electric fields, relevant for their implementation in optoelectronic applications.