Extraordinary Mass Transport and Self-Assembly: A Pathway to Fabricate Luminescent CsPbBr₃ and Light-Emitting Diodes by Vapor-Phase Deposition

Halide perovskites have been shown to be promising materials in making light-emitting diodes. At present, almost all of perovskite materials are made by solution-based synthesis. There are very limited reports on fabricating perovskite LEDs by vapor-phase deposition (VPD), a method that can be easily scaled up for commercial production. In this paper, dual-source VPD is used to fabricate stable CsPbBr₃ perovskite thin films with excellent luminescent properties. Scanning electron microscope and atomic force microscope studies show that CsPbBr₃ films, when coated with a thin LiBr overlayer, demonstrate an extraordinary mass transport at room temperature to re-assemble into well-defined islands. LiBr is also shown to passivate nonradiative defects and boost photoluminescence performance of the CsPbBr₃, improving the intensity by a factor of 11 for a nominal 18 nm perovskite film and leading to extremely narrow photoluminescence peaks (16 nm FWHM). This self-assembled perovskite LED shows major improvement in the electroluminescence performance, almost tripling the brightness of reference devices. X-ray photoelectron spectroscopy measurement shows that surface LiBr improves Cs/Pb chemical stoichiometry, reduces Br vacancies, and shift the Fermi energy level toward conduction band minimum.