Operando Multimodal Electron Microscopy of Perovskite Nano-LEDs: Nanoscale Degradation and Recovery Behavior

Understanding degradation mechanisms in halide perovskites under operation is crucial to improving device stability, yet direct nanoscale observation during electrical biasing remains challenging. Here, we report the fabrication of planar nano-perovskite LEDs integrated into an electron-transparent circuit, enabling simultaneous electrical, structural, and optical characterization of perovskite devices directly inside electron microscopes. In situ biasing shows that volatilization of Br2 accompanied by the formation of Pb0, PbBr2, and CsBr phases is significantly more pronounced at the cathodic region, indicating a pathway closely linked to cathodic reduction rather than anodic oxidation. The nano-LEDs also exhibit electroluminescence (EL) within the microscope, enabling temperature estimation via EL tracking, which is valuable for nanoscale devices in operando TEM, where thermal probing is difficult. Cathodoluminescence (CL) mapping further identifies regions susceptible to material loss prior to biasing through a characteristic red shift in the CL spectrum, highlighting the link between local defect density and electrical instability. Remarkably, applying a moderate reverse bias (≤7 V) induced reversibility of the degraded structure, while higher reverse biases promoted defect formation. These results establish a comprehensive in situ platform for probing degradation, recovery, and biasing strategies in perovskite optoelectronic devices.