Light-Induced Halide Sublimation and Diffusion in 2D Halide Perovskites

To address stability challenges in two-dimensional (2D) perovskite semiconductor materials, an improved understanding of the degradation origins and pathways under external stimuli is needed. Here, we investigate the evolution of halide redistribution within various 2D halide perovskites (<i>n</i> = 1 to 3) lateral heterostructures using <i>in-situ synchrotron </i>nanoprobe X-ray fluorescence (nano-XRF) microscopy. The heterostructures comprise distinguishable iodine (I) and bromine (Br) regimes laterally. Continuous UV exposure leads to iodine sublimation in high-dimensional 2D perovskites and a visible amount of Br diffusion to the previously iodine-rich regime. In contrast, bromine is relatively more stable than iodine in <i>n</i> = 2 and 3 heterostructures, with no significant change in total Br concentration. Additionally, combining nano-XRF mapping and X-ray absorption spectroscopy, we found a reduction of dimensionality in the previously iodine-rich regime in crystals with <i>n</i> &gt; 1 after UV exposure, indicating significant structural reconfiguration beyond ion migration. These findings provide new insights into the photo-induced ion migration and degradation mechanisms of 2D perovskite materials and shed light on future materials design.