Jeonbuk National University (JBNU) (President Yang O-bong) Professor Seunghee Lee's research team (Graduate School of Engineering, Department of Nano-Convergence Engineering, Department of Polymer-Nano Engineering, Dept. of JBNU-KIST Industry-Academia Convergence Research) Research Professor Minsu Kim has succeeded in developing a technology that maximizes the photoluminescence color-conversion efficiency of quantum dots for display applications using organic-inorganic composite nano-scatterers. 

Quantum dots enable displays with higher color reproducibility and a wider color gamut, and are thus attracting attention as next-generation display materials. To date, commercialized quantum-dot displays have implemented quantum dots in sheet form within a polymer matrix and placed them in front of liquid-crystal display backlights, or, more recently, produced premium TVs by using inkjet printing to form red and green pixels on top of blue OLEDs so that the blue light is color-converted to red and green at each pixel. This color conversion by which quantum dots absorb a specific color and emit another is called photoluminescence. Photoluminescence efficiency is a key factor when applying these materials to displays.

Until now, various quantum-dot synthesis methods have been used to increase photoluminescence efficiency. The research team developed a technology that achieves higher color-conversion efficiency from the same quantum dots by incorporating organic-inorganic composite nano-scatterers into the polymer matrix that houses the quantum dots. The nano-scatterers consist of a composite of polymer-dispersed liquid crystal (PDLC), a highly promising material for smart windows, and titanium dioxide nanoparticles, which have a high UV reflectance and are used as raw materials for UV blockers.

By forming a PDLC-type nano-scatterer via photopolymerization-induced phase separation, they optimized the optical path and scattering characteristics within the color-conversion layer so that blue light does not leak out without being converted but instead repeatedly encounters internal quantum dots, thereby maximizing color-conversion efficiency.

In inkjet printing, when using a mixture of quantum dots, titanium dioxide nanoparticles, and polymer resin, inorganic particles tend to cause nozzle clogging or precipitation in solution. By mixing anisotropic organic molecules with flowable characteristics, it is possible to form scatterers while mitigating precipitation and related issues. This approach secures material properties that are highly advantageous for solution stability and solvent-based processing.

As a result of this research, they confirmed that, when nano-scatterers were formed from a solution at an optimal concentration that remained stable for more than three days without precipitation or agglomeration, the external quantum efficiency (EQE) involved in color conversion increased up to 58.6%. 

Research Professor Minsu Kim said, “This approach provides a direction for increasing external quantum efficiency while maintaining high stability in solvent processing,” and added, “It is expected to be a technology that can be widely applied and adapted in quantum-dot displays.” 

The study involved Research Professor Minsu Kim, Dayeon Lee (M.S., graduated), and Hayoung Jeong (M.S. candidate). It was carried out with support from the National Research Foundation of Korea (Mid-Career Researcher Support Program) and the Ministry of Education's 4th phase Brain Korea 21 Program (BK21-FOUR), and was published under the title 'Superior photoluminescence of quantum dot displays via organic-inorganic composite scatterers' in Composites Part B: Engineering (IF=13.1), an international journal ranked in the top 1% in the field of composite materials and engineering.