■ 제 목: Overcoming Fundamental Limitations of Light-Emitting Nanomaterials for Next-Generation Displays
■ 연 사: 조힘찬 박사 (University of Chicago)
■ 일 시: 2020년 11월 10일(화) 오전 10시
■ 참가자 접속정보 (9:55분까지 참가를 부탁드립니다)
회의 ID: 808 075 7553
회의 비밀번호: 2020mse
회의 링크: https://kaist.zoom.us/j/8080757553
■ Abstract : In this talk, I will present my research to overcome fundamental limitations of light-emitting nanomaterials including metal halide perovskites and colloidal inorganic quantum dots (QDs) for their display applications. Before 2014, room-temperature electroluminescence from metal halide perovskites was considered as almost impossible due to strong exciton dissociation at room temperature. I have solved this problem by identifying fundamental efficiency-limiting factors and developing two novel strategies: (1) In-situ fabrication of perovskite nanocrystals based on crystallization control and (2) introducing quasi-2D structures with ligand-like A-site cations (Ruddlesden-Popper phase).[2,3] Those strategies led to a world-first breakthrough in brightness and efficiency of perovskite light-emitting diodes (LEDs) at room temperature (external quantum efficiency = 8.5%, which was >20,000 times higher than control and even comparable to those of organic LEDs and QD LEDs). These works greatly stimulated PeLED research and totally changed the paradigm of display industry that focused only on organic or QD emitters. On the other hand, precision patterning of QDs is a critical step to fabricate displays incorporating QD color filters and QD LED subpixels in form of RGB matrix. However, high-resolution patterning of solution-processed QD layers is fundamentally challenging because conventional patterning methods cannot simultaneously meet the requirements of high resolution, pattern uniformity, high throughput, and high PLQY. To overcome this challenge, I developed a direct, scalable, and nondestructive route for high-resolution patterning of QDs and QLEDs. A specially designed nanocrystal ink, “photopatternable emissive nanocrystals (PEN)”, consists of gradient core/shell QDs and photoacid generators which enable photochemically activated reactions leading to in-situ ligand exchange in the QD films. Uniform electroluminescence patterns of RGB QD LEDs with features size down to 1.5 µm were demonstrated while preserving the structural, electronic and emissive properties of patterned QDs.