A research team at Seoul National University, led by Prof. Tae-Woo Lee, has developed highly efficient large-area perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency (EQE) of 22.5% and pixel size of 102 mm2.
Professor Tae-Woo Lee's research team developed the scalable coating method of perovskite nanocrystals to make uniform large-area emitting films that helped fabricate these highly efficient large-area PeLEDs.
Current high-efficiency, large-area PeLED research is usually based on bulk polycrystalline thin films. Since the bulk polycrystalline perovskite is simultaneously crystallized during the film formation, the quality of the fabricated PeLED is severely affected by the environment and thus the reproducibility is limited. Typically in large-area PeLEDs, it is hard to control the crystal growth to achieve small and fine nanograins. Additionally, the spin-coating method, which is widely accepted in PeLED research, has inherent limitations on uniformity and mass-production of large-area thin film. Therefore, previously reported PeLEDs showed significant efficiency drop in large-area devices.
Professor Tae-Woo Lee and his research team have suggested that overcoming the previous intrinsic problems in large-area device can be realized by the use of colloidal perovskite nanocrystals which have a size of several nanometers. In such a small dimension, charge carriers can be spatially confined to achieve high luminescence efficiency and organic ligands present in the surface of the nanocrystal can effectively suppress the ion migration and charge trapping. Also, highly uniform and reproducible large-area thin films can be achieved with colloidal perovskite nanocrystals which decouples the crystallization of perovskite from the film formation process.
The Seoul National University research team developed simple modified-barcoating which facilitates the evaporation of residual solvent. PeLEDs that incorporated the uniform modified-barcoated perovskite nanocrystal films achieved EQE of 23.26% and EQE of 22.5% in a large pixel area of 102 mm2 with high reproducibility.
Prof. Tae-Woo Lee said, “This study has developed a technology essential for manufacturing large-area devices, which was the biggest obstacle to commercialization of PeLEDs.” He also commented “It is expected to contribute to the commercialization of PeLEDs by providing the way toward a development of large-scale industrial displays and solid-state lighting that uses perovskites”.