Atomic-scale visualisation of interfacial degradation in halide perovskites via multidimensional in-situ electron microscopy

Halide perovskite light-emitting diodes (PeLEDs) promise high-efficiency, low-cost optoelectronics, yet their operational instability remains a critical barrier to practical deployment. Here, we develop a multimodal in-situ electron microscopy approach that integrates four-dimensional scanning transmission electron microscopy (4D-STEM), energy-dispersive X-ray spectroscopy (EDS), and atomic-resolution imaging to directly visualize structural and chemical evolution in a working PeLED with nanometre precision. Our in-situ biasing measurements uncover nanoscale structural and chemical transformations initiated at transport layer interfaces, including the formation of metallic lead and lead-rich secondary phases, as well as strain-driven grain fragmentation. Upon biasing, we observe the partial transformation of the metallic Al contact to insulating AlCl₃. Crucially, while the perovskite emitter’s bulk remains relatively intact, our experiment shows that degradation is localized at interfaces. By comparing in-situ and ex-situ measurements, these results establish a mechanistic link between interfacial strain, ionic transport, and electrochemical reactions in working devices, and provide a broadly applicable framework for nanoscale degradation analysis in complex multilayered optoelectronic systems using multimodal in-situ biasing microscopy.