A CsPbBr₃/ZIF-8 nanocomposite with uniform nanocrystal distribution and strong interfacial coupling achieved through ligand exchange exhibits efficient charge separation and enhanced photocatalytic activity.

CsPbBr₃ (CPB) perovskite nanocrystals (NCs) have attracted considerable interest due to their outstanding charge carrier mobility, long diffusion lengths, and efficient visible light absorption, making them ideal candidates for photocatalysis, light-emitting diodes (LEDs), solar cells, and photodetectors. However, their practical applications are limited by poor environmental stability. We employed a metal-organic framework (MOF) to address this challenge as a stabilizing matrix, selecting ZIF-8 for its exceptional thermal and chemical stability, high surface area, and versatile synthesis routes. The CPB/ZIF-8 nanocomposite was synthesized by integrating hot-injection-produced CPB nanocrystals with ZIF-8 using an optimized mixing approach, ensuring a uniform NCs distribution. Electron microscopy (EM) analysis confirmed the well-controlled and uniform distribution of the NCs on the surface of the ZIF-8. Moreover, the Fourier-transform infrared spectroscopy (FTIR) revealed ligand exchange, where the imidazole linkers of the ZIF-8 structure replace the NCs ligands. The process promotes almost epitaxial attachment of the latter, thus promoting effective charge interactions in the integration process. The unshifted absorbance spectra verified the preservation of optical activity, whereas a 92% quenching in photoluminescence (PL) indicated efficient charge separation and reduced electron-hole recombination. To investigate charge transfer mechanisms, photocatalytic dye degradation under visible light irradiation was employed using methyl orange (MO) and bromocresol green (BCG) as model dyes. The CPB/ZIF-8 nanocomposite exhibited significantly enhanced photocatalytic performance, achieving 1.48 and 1.75 times higher degradation rates for MO and BCG, respectively, compared to pristine CPB NCs. Electron paramagnetic resonance (EPR) studies demonstrated superior radical generation capabilities, particularly hydroxyl radicals (•OH), further confirming enhanced charge transfer and photocatalytic efficiency. These findings underscore the synergistic interaction between CPB NCs and ZIF-8, positioning the CPB/ZIF-8 nanocomposite as a promising material for photocatalysis and optoelectronic applications.

Zero-dimensional (0D) and three-dimensional (3D) halide perovskite nanocrystals (HP-NCs), owing to their unique optoelectronic properties, are extensively studied for photocatalytic activity. However, HPs are highly sensitive to light, humidity, and other environmental factors, which accelerate their decomposition. Understanding the decomposition process is crucial for gaining insights into how to stabilize HP-NCs. Here, we investigate the radical-driven decomposition process and dynamics of the 0D C4PbBr6 and 3D CsPbBr3 NCs under the influence of visible light and a polar solvent by electron paramagnetic resonance (EPR) spectroscopy. Our findings indicate that light accelerates radical formation over time, making the decomposition of HP-NCs a self-sustaining process. Upon illumination of the NCs, hydroperoxyl radicals are formed first, followed by unconventional Br, Cs, and Pb-related radicals, indicating the initiation of NC decomposition. The decomposition of CsPbBr¬3 NCs starts after 3 min of light exposure, while C4PbBr6 NCs take 18 min, indicating the greater stability of the latter. Additionally, we evaluated the photocatalytic activity of the HPs toward degrading organic dyes. The 3D CsPbBr3 NCs performed as superior photocatalysts compared to their 0D Cs4PbBr6 NCs counterparts. Yet, linking the results of EPR measurements with the photocatalytic efficacy suggests that the CsPbBr3 NCs undergo degradation during the photocatalytic process, thereby serving as a sacrificial agent to enhance photocatalytic activity. The understanding derived from EPR spectroscopy in tracking radical formation and dynamics can be extended to enhance the stability and efficiency of various nanomaterials in optoelectronic and photocatalytic applications, thus contributing to advancements beyond the HP family.

Halide perovskites (HPs) exhibit outstanding optoelectronic properties, making them highly attractive for advanced photonic and electronic applications. Among them, cesium lead bromide (CsPbBr₃) exhibits high photoluminescence efficiency, narrow emission linewidths, and excellent color purity, making it suitable for light-emitting diodes, photodetectors, scintillators, and lasers. However, its practical application remains limited by intrinsic instability and environmental stressors such as moisture, heat, oxygen, and illumination. This review discusses the fundamental degradation mechanisms in HPs, using CsPbBr₃ as a representative system, primarily in nanocrystals (NCs), while also considering thin-film and bulk forms. Intrinsic instability arises from the soft ionic lattice, a relatively low tolerance factor, and anharmonic lattice dynamics, which promote defect formation, ion migration, and structural distortion. Low activation energies for ionic transport enable migration of halide (Br⁻) and A-site (Cs⁺) ions, leading to defect accumulation, non-radiative recombination, and phase instability. In NCs, surface-dominated effects further accelerate degradation, driven by high defect densities and ligand desorption. Extrinsic factors promote degradation through hydrolysis, photoinduced defect formation, radical-driven reactions, and transformation into secondary phases. These processes can be intensified when multiple environmental stressors act simultaneously, reducing operational stability. These processes form a coupled, condition-dependent degradation network. Their interactions and relative contributions depend on the material form and environmental or operational conditions. Overall, this review highlights the interconnected roles of lattice dynamics, defect formation, ionic transport, and environmental interactions in governing the instability of CsPbBr₃-based HPs.