Understanding perovskite light-emitting diodes through transmission electron microscopy: materials structure, optical regulation and devices

Perovskite light-emitting diodes (PeLEDs) hold great promise in various fields such as displays, lighting, and optical communications. The external quantum efficiency (EQE) of advanced green, red, and near-infrared PeLEDs has already surpassed 20%. To effectively promote the development of PeLEDs, the ability to accurately characterize the structure and composition of perovskite materials is crucial. The comprehensive transmission electron microscopy (TEM) techniques, which combine high-resolution imaging, diffraction, in-situ structural measurements and spectroscopic analysis, allow for in-depth characterization in the temporal, spatial, momentum, and even energy domains with outstanding resolution. In this review, we present the latest advances in PeLEDs and systematically review notable strategies for optimizing the microstructure and charge behavior of perovskite emitters, such as metal ion doping, compositional engineering, organic ligand surface passivation, and size engineering. Additionally, we highlight the significant applications of TEM in PeLEDs. This technique can provide information regarding morphology, crystal structure, composition, surface ligand, interface and stability of perovskite emission layer, which facilitates phase identification, compositional analysis, and degradation mechanism determination, among others. The purpose of this review is to guide future characterizations of these electron beam-sensitive materials via TEM, and provide comprehensive perspective and reference for highly efficient PeLEDs.