Direct Observation of Stimulus-Dependent Degradation Pathways in Metal Halide Perovskites via Light-Coupled Atmospheric In Situ Gas-Cell TEM

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Over the past decade, perovskite solar cells (PSCs) have achieved remarkable performance gains with power conversion efficiencies exceeding 25%, approaching those of leading silicon photovoltaic technologies while offering potentially lower production costs [1, 2]. However, their operational instability under environmental stressors such as moisture, heat, and light illumination remains a critical barrier to long-term deployment compared to conventional silicon technology [2]. While light exposure is critical for generating photoexcited charge carriers in metal halide perovskites (MHPs), it simultaneously induces ion migration, phase segregation, and degradation, severely limiting device longevity [3]. As MHPs often fail or degrade during operation, understanding the interplay between external stimuli and intrinsic material instability is therefore essential for improving perovskite device reliability. In situ gas-cell transmission electron microscopy (GC-TEM) has emerged as a powerful platform for directly visualizing the structural and compositional evolution of catalytic and solar cell materials under realistic environments. Here, we employ a novel optical-fiber-coupled atmospheric GC-TEM holder and an ultra-thin silicon nitride (SiNx) microchip [4] to study the stability of MHPs under different gas environments, electron-beam dose conditions, and light illumination. By systematically varying the imaging dose and performing dedicated dose-controlled experiments, we reliably decouple electron-beam effects from light-driven transformations, which is critically important for studying beam- and light-sensitive processes with optical-fiber-coupled GC-TEM. We demonstrate that the electron-beam-induced decomposition of CsPbBr3 is faster in Ar than in vacuum, indicating a radiolysis-driven chemical process involving halide loss and the formation of metallic Pb, with degradation rates increasing at higher electron fluxes. Moreover, we captured the light-driven formation of nanoscale Pb-rich domains in real-time, which preferentially nucleate at grain boundaries. Our observations demonstrate that electron irradiation and light illumination activate fundamentally distinct degradation pathways in CsPbBr3, providing in situ insight into stimulus-dependent degradation mechanisms relevant to real device operating environments. Experiments were conducted using an aberration-corrected JEOL ARM200CF S/TEM (200 kV) equipped with a Gatan OneView CMOS camera and Protochips Atmosphere system [5].