Over the past decade, metal halide perovskites have garnered significant attention for their exceptional optical, electronic, and optoelectronic properties. Lead-based perovskites have been extensively studied as light-harvesting materials in photovoltaic technologies [1]. So far, metal halide perovskites have been applied in wide range of fields including photovoltaic cells, solar-to-fuel energy conversion devices, light-emitting diodes (LEDs), lasers, photodetectors, scintillators, thin-film transistors, and waveguides [2].
To address the toxicity associated with lead-based perovskites, researchers have shifted focus toward developing lead-free alternatives. Recently, all-inorganic copper halides, such as CsCu₂X₃ (X = Cl, Br), have emerged as promising candidates due to their enhanced air and thermal stability [3].
Here we show the structural stability of Cs₃Cu₂Cl₅ nanocrystals under ambient-like environments and photon illumination using a combination of in-situ transmission electron microscopy (TEM), synchrotron-based diffraction, and cathodoluminescence microscopy. In order to decouple the effects of external stimuli from the electron beam induced changes, the electron beam irradiation effects on Cu halides has been firstly investigated. Using electron diffraction and high-resolution TEM imaging, we found that Cu halides exhibit nearly tenfold greater electron beam stability compared to all-inorganic lead-based perovskites under low to medium dose fluences. Unlike lead-based halides, where Pb segregates into nanoparticles under beam exposure, Cu halides degrade via distinct mechanisms, influenced by their crystal size and the presence of surface ligand. These findings offer insight into the structural degradation mechanisms of Cs₃Cu₂Cl₅ which are important for their applications in optoelectronic devices.