Charge-Carrier Behavior and Molecular Interface Engineering in Perovskite Light-Emitting Diodes

Molecular interface engineering has become increasingly important for improving the efficiency and stability of perovskite light-emitting diodes (PeLEDs). Although highly emissive perovskite materials have advanced rapidly, their translation into high-performance devices remains limited by interfacial losses, unbalanced charge injection, and instability under electrical operation. In this review, we first discuss charge-carrier behavior in perovskite materials and devices, with emphasis on radiative and non-radiative recombination, carrier accumulation under injection, and the device-level consequences of interfacial constraints. We then examine the development of interfacial molecular strategies in PeLEDs, including self-assembled monolayers and related interfacial molecules, and summarize how such molecular layers influence charge injection, interfacial recombination, local electronic structure, and film formation at both charge-injection interfaces. On this basis, we further consider the implications of these interfacial effects for molecular regulation in light-emitting devices, with particular attention to electronic regulation under bias, chemically persistent passivation, and structural compatibility with emissive-layer formation. By connecting carrier physics, interfacial function, and molecular regulation, this review aims to provide a clearer framework for understanding and developing molecular interfacial strategies for high-performance PeLEDs.