Joint research team develops new method to produce high-efficiency perovskite LEDs
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0 From left in the top row are Kim Young-hoon, a professor in the Department of Chemistry at Kookmin University; Kim Ji-geon, a researcher at the university; and Lee Yu-bin, who has completed her master’s coursework at the university. From left in the bottom row are Lee Bo-ram, a professor in the Department of Advanced Materials Science and Engineering at Sungkyunkwan University; Seok Gyeong-eun, a researcher at the university; and Lee Tae-kyung, a professor in the Department of Organic and Nano Engineering at Hanyang University. Courtesy of Kookmin University
A joint research team from Kookmin University, Sungkyunkwan University and Hanyang University has developed highly efficient perovskite light-emitting diodes (LEDs) without the need for a separate post-synthetic ligand-exchange process.
The findings were published in Advanced Functional Materials, an international journal in the field of materials science, under the title “Direct Integration of Conductive, Emissive Perovskite Nanocrystals into Efficient Light-Emitting Diodes Without Post-Synthetic Ligand Exchange.”
The team was led by Kim Young-hoon, a professor in the Department of Chemistry at Kookmin University; Lee Bo-ram, a professor in the Department of Advanced Materials Science and Engineering at Sungkyunkwan University; and Lee Tae-kyung, a professor in the Department of Organic and Nano Engineering at Hanyang University.
The three professors served as co-corresponding authors of the collaborative study.
Lee Yu-bin, who has completed her master’s coursework at Kookmin University, also participated as a co-first author alongside Kim Ji-geon, a researcher at the university, and Seok Gyeong-eun, a researcher at Sungkyunkwan University.
Kookmin University said Lee contributed to key parts of the study, including analyzing the surface properties of perovskite nanocrystals and applying them to light-emitting devices, highlighting her research expertise in next-generation optoelectronic materials and devices.
Perovskite nanocrystals have emerged as promising materials for next-generation display LEDs owing to their high luminescence efficiency, excellent color purity and solution processability.
However, nanocrystals produced using conventional synthesis methods have surfaces covered with large amounts of organic ligands with long hydrocarbon chains, which impede charge transport between nanocrystals.
As a result, fabricating high-performance devices has generally required a post-synthetic ligand-exchange process to replace these long-chain ligands with shorter ones.
To overcome these limitations, the research team controlled the surface chemistry of the nanocrystals from the synthesis stage using a heat-up synthesis method based on a bimolecular nucleophilic substitution reaction.
The team developed perovskite nanocrystal films that exhibited lower energetic disorder and more ordered crystalline structures than films made from conventionally synthesized nanocrystals. Charge transport between the nanocrystals was also significantly enhanced.
A schematic illustration of perovskite nanocrystal technology / Courtesy of Kookmin University
Building on these improvements, the team achieved a maximum external quantum efficiency of 11.4 percent in LEDs that directly incorporated the nanocrystals into the emissive layer without a separate post-synthetic ligand-exchange process.
This was approximately four times higher than the 2.7 percent achieved by devices using conventionally synthesized nanocrystals.
The study demonstrates that excellent luminescence and electrical conductivity can be achieved without the post-synthetic ligand-exchange process previously required for high-performance perovskite nanocrystal devices.
By precisely controlling the surface ligand density and halide passivation of nanocrystals during synthesis, the approach is expected to simplify LED fabrication and expand the potential applications of these materials in other optoelectronic technologies.
