Prof. Doh C. Lee (KAIST, South Korea)
Wednesday, March 27th, 2024, 10:30-12:00, L0411 (Building 4, Koganei Campus)
Title: Enhancing Quantum Dot Light Emitting Devices: Sub-Bandgap Turn-On and Electrobrightening via Advanced Charge Transport Layer Engineering
Prof. Doh C. Lee
Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Korea
Over the past decade, QD-LEDs have experienced remarkable improvements in device efficiency, yet the mechanism behind barrierless hole injection at voltages below the bandgap remained elusive. Our research team has identified the Fermi level alignment, influenced by surface states, as the key factor enabling this phenomenon. This alignment, coupled with the macroscopic electrostatic potential gain from the restructured energy environment, facilitates hole injection into quantum dots. Contrary to previous assumptions, we demonstrate that the energy level alignment significantly outweighs the local carrier injection barrier alteration caused by the Coulombic force of a charge in quantum dots. Our findings elucidate the mechanism of barrierless carrier injection in QD-LEDs and propose a broader design principle for efficient electroluminescent systems utilizing nanocrystal emitters. Additionally, I will discuss the electrobrightening effect observed in quantum dots using ZnMgO as an electron transport layer instead of ZnO. 過去10年間、量子ドット発光デバイス（QD-LED）は効率の向上において驚くべき進展を遂げてきましたが、バンドギャップ以下の電圧での障壁のないホール注入のメカニズムは未解明でした。私たちの研究チームは、表面状態に影響を受けるフェルミ準位の整列を、この現象を可能にする鍵として特定しました。この整列は、再構築されたエネルギー環境からの巨視的な静電ポテンシャルの利得と組み合わさり、量子ドットへのホール注入を促進します。従来の仮定とは異なり、エネルギーレベルの整列が、量子ドット内の局所キャリア注入バリアの変化を、クーロン力によるものよりも大幅に上回ることを示しています。私たちの研究結果は、QD-LEDにおける障壁のないキャリア注入のメカニズムを明らかにし、ナノクリスタル発光体を利用した効率的な電気発光システムの広範な設計原則を提案しています。さらに、ZnOの代わりに電子輸送層としてZnMgOを使用した量子ドットで観察される電気明るさ効果についても議論します
References
H. Lee, B. G. Jeong, W. K. Bae, D. C. Lee, J. Lim, “Surface state-induced barrierless carrier injection in quantum dot electroluminescent devices.” Nature Communications 12, 5669 (2021).
Doh C. Lee is a Professor in the Dept. of Chemical and Biomolecular Engineering at Korea Advanced Institute of Science and Technology (KAIST). Since 2001, he has been a director of both Energy and Environmental Research Center (EERC) and Quantum Materials Research Center (QMaRC) at KAIST. He received both his B.S. and M.S. degrees in Chemical Engineering from Seoul National University. His Master’s thesis under the supervision of Prof. Sang Heup Moon entails Dr. Lee’s research results on the heterogeneous catalysis of selective hydrogenation of 1,3-butadiene to 1-butene. He then moved to the University of Texas at Austin and completed his Ph.D study in 2007 under the supervision of Prof. Brian Korgel. For his thesis work on magnetic interactions in ferromagnetic and superparamagnetic nanocrystals and solution-phase synthesis of silicon nanowires and carbon nanotubes, he was awarded a Harrington Dissertation Fellowship in 2006, a prestigious recognition given to two graduate students per year from the entire campus. In 2007, he joined the research group of Dr. Victor Klimov at Los Alamos National Laboratory as a Director’s Postdoctoral Fellow and worked in the exciton dynamics of quantum dots. His current research focus is the study of heterostructure quantum dots for their use in light-emitting device applications and photochemical reactions for solar-to-fuel conversion. Prof. Lee is expanding his research interests into hydrogen production, such as water electrolysis and dry reforming of methane.
Host: Satria Zulkarnaen Bisri, Sustainable Quantum Nanomaterials and Devices (SEMANTICS), Dept. Applied Physics & Chemical Engineering, Tokyo University of Agriculture and Technology.