Researchers from Tsinghua University, Nanjing Tech University, University of Chinese Academy of Sciences and The Hong Kong Polytechnic University have reported a new way to make deep-blue perovskite LEDs much brighter and more stable. Their work focuses on growing ultra-smooth, defect-poor single-crystal thin films that unlock efficient deep-blue emission for future displays and lighting.
The team developed in situ–grown single-crystal thin films of the 2D perovskite PEA₂PbBr₄ using a carefully controlled crystal growth process in air. These films are large-area, highly ordered, and atomically smooth, with a trap density far lower than conventional polycrystalline perovskite films. To achieve this film quality, they combined a two-stage thermal annealing process with a spatially confined growth setup using a specially treated, highly hydrophobic cover glass. Additives such as excess PEABr and a polymer (PVP) were used to slow down nucleation, improve crystal quality, and further boost the photoluminescence efficiency while keeping the surface extremely flat.
Compared with standard polycrystalline films, these single-crystal thin films have far fewer grain boundaries, much lower defect density, and much higher stability in air. As a result, they emit light more efficiently, with a narrow deep-blue spectrum and reduced nonradiative losses that usually plague wide-bandgap perovskites.
Using these engineered films, the team built deep-blue LEDs with a typical stack of ITO/PTAA/perovskite/TPBi/LiF/Al and a perovskite layer about 2.4 micrometers thick. Even at this thickness, the devices showed efficient charge transport and reached a luminance of 179 cd m⁻² at 419 nm, among the brightest deep-blue 2D perovskite LEDs reported so far, although the external quantum efficiency still leaves room for future improvement.
The study links better crystal quality and fewer specific defects (especially problematic bromide vacancies in the perovskite plane) directly to higher efficiency and narrower emission. This positions single-crystal perovskite thin films as a promising platform for practical deep-blue emitters in next-generation displays, solid-state lighting, and potentially laser applications.
