Lee Yu-bin, a student on the research team led by Professor Kim Younghoon of the Department of Chemistry at Kookmin University (President Jeong Seung Ryul), in collaboration with Professor Lee Bo Ram of Sungkyunkwan University, and the research team led by Professor Lee Tae Kyung at Hanyang University, has published a research paper titled “Direct Integration of Conductive, Emissive Perovskite Nanocrystals into Efficient Light-Emitting Diodes Without Post-Synthetic Ligand Exchange” in *Advanced Functional Materials*, a world-renowned international journal in the field of materials science. This journal is a world-renowned publication covering innovative research across the entire field of materials science, including functional materials, nanotechnology, chemistry, and physics. With an Impact Factor of 19.9, it ranks among the top 5% of journals according to the JCR.

Perovskite nanocrystals (PNCs) are attracting attention as a key material for next-generation display light-emitting diodes (LEDs) due to their high luminous efficiency, excellent color purity, and solution processability. However, the surfaces of perovskite nanocrystals produced using conventional synthesis methods contain large amounts of organic ligands with long hydrocarbon chains; these ligands are highly electrically insulating and hinder charge transport between nanocrystals. Consequently, to fabricate high-performance devices, a separate “post-synthetic ligand exchange” process—in which long ligands are replaced with short ones after synthesis—has generally been required.

To address this issue, the research team controlled the surface chemistry of the nanocrystals from the synthesis stage onward using an SN2-reaction-based heat-up synthesis method. This allowed them to significantly reduce the amount of oleate ligands present on the surface of conventional nanocrystals and, instead, realize CsPbBr₃ perovskite nanocrystals with low ligand density, stabilized by a Br⁻-rich surface. In particular, experimental and theoretical calculations demonstrated that the OAM/Br⁻ surface combination forms more stable surface bonds than the conventional OAM/oleate combination, thereby suppressing surface defect formation and maintaining excellent optical properties despite the low organic ligand density.

Furthermore, the developed perovskite nanocrystal thin film exhibited lower energy disorder and improved crystal alignment characteristics compared to nanocrystals synthesized by conventional methods, and charge transport between nanocrystals was also significantly enhanced.

Consequently, a maximum external quantum efficiency (EQE) of 11.4% was achieved in an LED in which the nanocrystals were directly incorporated into the emissive layer without undergoing any separate post-synthesis ligand exchange process. This represents an approximately fourfold improvement compared to the 2.7% achieved by devices using perovskite nanocrystals synthesized via conventional methods.

The maximum luminance also improved more than fivefold, from 59 cd m⁻² to 314 cd m⁻², while the full width at half maximum (FWHM) of the emission spectrum decreased from 21 nm to 17 nm, simultaneously achieving high color purity.

The greatest significance of this study lies in demonstrating that the post-synthesis ligand exchange process—long considered an essential step for realizing high-performance perovskite nanocrystal devices—can be omitted. By precisely controlling the surface ligand density and halide passivation of the nanocrystals from the synthesis stage onward, the team simultaneously achieved excellent luminescence characteristics and high electrical conductivity, and demonstrated that these can be directly applied to actual LED devices. These results are expected to simplify the fabrication process for future light-emitting devices utilizing perovskite nanocrystals and expand the potential for their direct application in various optoelectronic devices.

Notably, Lee Yu-bin, a student in the Department of Chemistry at Kookmin University, participated as a co-first author alongside Researcher Kim Ji-geon and Researcher Seok Gyeong-eun of Sungkyunkwan University, further enhancing the significance of this research. Lee Yu-bin contributed to the study by analyzing the surface properties of perovskite nanocrystals and applying them to light-emitting devices, thereby demonstrating her research capabilities in the field of next-generation optoelectronic materials and devices.

Meanwhile, this study featured Researcher Kim Ji-geon and student Lee Yu-bin from Kookmin University, along with Researcher Seok Gyeong-eun from Sungkyunkwan University, as co-first authors, while Professor Lee Tae Kyung of Hanyang University, Professor Lee Bo Ram of Sungkyunkwan University, and Professor Kim Younghoon of Kookmin University served as co-corresponding authors.