Precisely controlled organic halide evaporation for efficient vacuum-deposited perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) represent a compelling platform for next-generation display technologies owing to their unique optoelectronic properties. Although vacuum deposition offers the scalability and uniformity required for commercialization, vacuum-deposited PeLEDs typically exhibit lower external quantum efficiencies (EQEs) than their solution-processed counterparts. Addressing this challenge requires innovative strategies to achieve carrier confinement and suppress non-radiative recombination. In this study, we prepare high-efficiency vacuum-deposited PeLEDs through the precise compositional tailoring of Cs1−xMAxPbBr3 nanocrystals (NCs; MA = methylammonium) embedded within a wide-bandgap Cs4PbBr6 matrix via controlled co-evaporation. The addition of a small amount of PbBr2 to MABr significantly enhances the evaporation stability of the latter as well as the uniformity of the resulting films, thereby enabling controlled growth of Cs1−xMAxPbBr3 NCs. The MA content (x) in the resulting Cs1−xMAxPbBr3/Cs4PbBr6 nanostructures is precisely tuned and monitored in situ using a residual gas analyzer. At the optimal x (0.19), we achieve a remarkable 1.9-fold EQE enhancement compared with that of the MA-free device. This improvement is attributed to the controlled incorporation of MA cations, which increases the average NC size and inter-particle spacing. Structural modifications enhance photoluminescence intensity and prolong exciton decay lifetimes, indicating suppression of non-radiative recombination pathways associated with surface defects.