Visualizing Bulk Heterogeneities in CsPbBr₃ Single Crystals via Two-Photon Photoluminescence Microscopy

Halide perovskites are renowned for their high performance in photovoltaics and LEDs and have recently shown great promise as next-generation radiation detectors. Despite rapid advancements in device performance, their full potential remains limited by microscale heterogeneity and defects that impede local charge transport properties. Contrary to visible light, which has a short absorption depth, X-rays and gamma rays penetrate much deeper, requiring millimeter-thick single crystals. This means conventional one-photon excitation techniques are insufficient for providing a full picture of the crystal properties owing to their surface-limited nature. In this work, we combine one-photon and two-photon confocal photoluminescence microscopy to probe both the surface and bulk of cesium lead bromide single crystals. By systematically comparing Bridgman-grown crystals of varying quality, we identify a consistent trend linking photoluminescence properties to radiation detection performance. Under one-photon excitation, high-quality crystals exhibit marginally larger diffusion coefficients and 3–5 times longer carrier lifetimes, leading to enhanced diffusion lengths and charge transport. Strikingly, two-photon photoluminescence maps reveal more morphological defects within the bulk of low-quality crystals, with two-photon diffusion measurements further showing that these defects curtail local carrier diffusion. This work directly visualizes spatial heterogeneity buried within the bulk and quantifies its impact on the diffusion of charge carriers. These findings underline the importance of achieving homogeneous crystallization to improve bulk quality and the performance of perovskite radiation detectors.