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Professors Jin Young Oh of the Department of Chemical Engineering and Seong Jun Kang of the Department of Advanced Materials Engineering for Information & Electronics developed new light emitting polymer materials for stretchable displays and secured the next-generation display source technology

Stretchable displays are attracting attention as the next generation form factor after the foldable displays, and this research has provided a key piece of technological improvement in terms of stretchable light-emitting semiconductor materials that are essential for full-scale development of stretchable displays. The research result was published on June 22 in the prominent academic journal Science Advances (IF 14.980) under the title, “Intrinsically stretchable three primary light-emitting films enabled by elastomer blend for polymer light-emitting diodes.”

Innovative mixture of light emitting semiconductor and elastomer molecular unit which stretches like rubber while emitting light
In tandem with the recent development of polymer light emitting diode (OLED/PLED) material technology, stretchable light emitting material called “Super Yellow” has also been introduced, which can only emit greenish yellow light and require to be mixed with a polar material. Professor Oh emphasized, “In order to create a stretchable display, a light-emitting material that can implement all three primary colors of light―red, green, and blue (RGB)―is essential.”

Materials used for stretchable displays must be capable of producing the three primary colors of light while remaining constantly elastic. To develop a light-emitting material that meets these requirements, the research team used polymer light-emitting semiconductor that implements the three primary colors of light and elastomer (rubber). In previous studies, the mixing between the polymer light emitting semiconductor material and the elastomer did not go smoothly, resulting in excessive phase separation which limited the elasticity of the light emitting semiconductor material. Professor Oh said, "In this study, we formed a nanostructure with thin film heat treatment so that the combined material can be stretched at similar surface energy and intermolecular mixing can smoothly occur."

New light-emitting polymer material can be used in any industry requiring a display
The new material developed by the research team maintained a brightness of over 1,000 cd/m2 even at low voltage (less than 5v) and maintained stable luminosity performance even after undergoing 1,000 elasticity stress tests. Professor Kang emphasized, “This study has great potential for expansion and practical application. If various light emitting materials are mixed with elastomers, new functionality can be imparted. If an inorganic material-based light emitting material was used, for instance, it may exhibit improved material stability. It is of great significance that we have secured source material technology with this research breakthrough.”

The new light-emitting material can bring a significant leap forward to the development of the stretchable display industry. Professor Oh stressed, “The new stretchable display can be used in many ways.” It can be applied not only to consumer electronics such as stretchable smartphones, but also to the development and expansion of wearable displays such as robots and electronic skin, so it can be used in all industries that require displays. The research team now plans to focus on integrating diverse properties and functionalities to the materials, such as self-healing by grafting self-healing materials or auto-luminosity sensing with electro-optical devices that sense light.

The two subdivisions of the research team each focused on its strength in that Professor Oh’s division studied materials and Professor Kang's division researched optical devices. Professor Kang said, “I am proud that the combined talents and strengths of our Kyung Hee community have achieved outstanding results.” In addition, the first authors of the research article, Students Min Woo Jeong (Chemical Engineering, Ph.D. 1st term) and Jin Hyun Ma (Advanced Materials Engineering for Information & Electronics, Master’s 3rd term) are former undergraduate research students. Student Jeong said, “When I first entered the University, I only had a vague interest in research. But in my sophomore year, I was able to identify my area of interest while taking major courses. After a lab meeting with my professor, I was convinced that I should enroll into the undergraduate research student program. I learned so much from the professor's sincere attitude toward research, and even after entering graduate school, I am still very much interested in research.” This research project was supported by the National Research Foundation of Korea and the Korea Evaluation Institute of Industrial Technology.