Hole Delayed-Release Effect of Inorganic Interfacial Dipole Layer on Charge Balance for Boosting CsCuI Light-Emitting Diodes.

CsCuI light-emitting diodes (LEDs) have attracted tremendous interest due to their environmental friendliness, low-cost processing, and broadband luminescence properties. However, their hole injection efficiency usually towers over electron injection efficiency owing to the intrinsic Cu vacancy-mediated excess hole concentration and wide bandgap of CsCuI, generating severe charge imbalance. Here, we designed an inorganic interfacial dipole layer (IDL) based on lithium chloride to exert a hole delayed-release effect for charge balance in CsCuI LEDs by selectively modulating the energy levels of the contact layers. Accordingly, the IDL-based CsCuI LEDs exhibit a record champion brightness of 2620 cd/m along with a three times enhanced peak external quantum efficiency of 3.73% at 565 nm. Meanwhile, the universality of the hole delayed-release effect of inorganic IDLs is verified by demonstrating enhanced CsCuI LEDs incorporated with other alkali metal salt-based IDLs. This work provides a comprehensive guideline for optimizing the charge transport of lead-free LEDs by charge delayed-release effect of IDLs toward next-generation eco-friendly display applications.