Interface Engineering in Perovskite Light-Emitting Diodes: Fundamentals, Characterization, Strategies, and Applications

Interface engineering has emerged as a critical strategy for advancing perovskite light-emitting diodes (PeLEDs), enabling remarkable improvements in the device efficiency, stability, and spectral purity. This Review provides a comprehensive overview of interface engineering in PeLEDs, beginning with the fundamental principles that govern carrier injection, transport, and recombination at heterojunctions between perovskite emitters and charge-transport layers. We then survey advanced characterization techniques, including photoelectron spectroscopy, scanning probe microscopy, and time-resolved optical methods, that elucidate interfacial energy-level alignment, defect states, charge dynamics, and degradation pathways. On the basis of these insights, we systematically discuss versatile engineering strategies, such as self-assembled monolayers, dipole interlayers, dimensional regulation, and passivation schemes, to mitigate non-radiative recombination, balance charge fluxes, and enhance operational stability. Finally, we highlight emerging applications spanning high-resolution displays, flexible lighting, and lasing while outlining key challenges and future directions toward commercial realization. This Review aims to offer a holistic framework linking interfacial design to device performance, guiding next-generation PeLED development.