https://scholar.dgist.ac.kr/handle/20.500.11750/231 2026-04-04T13:36:29Z https://scholar.dgist.ac.kr/handle/20.500.11750/58943 Title: Boosting Efficiency and Longevity of Quantum Dot Light-Emitting Diodes with Dibenzofuran-Incorporated Hole Transport Materials Featuring High Bond Dissociation Energy Author(s): Hwang, Youngjun; Jung, Hyeonwoo; Kim, Jongyoun; Lee, Dongwoo; Lee, Youngu Abstract: The intrinsic degradation of quantum dot light-emitting diodes (QLEDs) is often attributed to the insufficient stability of hole transport materials (HTMs), which adversely affects both efficiency and operational lifetime. Despite efforts to address this issue, HTMs with high bond dissociation energy (BDE) for enhanced QLED performance remain underdeveloped. Here, a series of dibenzofuran (DBF)-incorporated HTMs with high BDE is synthesized to improve QLED efficiency and longevity. Among them, poly(9,9-dioctylfluorene-co-N,N-diphenyldibenzo[b,d]furan-1-amine) (1-PFDBF) exhibits superior hole mobility, high BDE, extended exciton lifetime, and reduced trap density. Green QLEDs employing 1-PFDBF achieve a maximum external quantum efficiency (EQEmax) of 25.71%, a maximum current efficiency of 102.98 cd A(-)(1), and a maximum power efficiency of 75.69 lmW(-)(1), significantly outperforming poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)diphenylamine) (TFB)-based QLEDs. Notably, the EQEmax of 1-PFDBF-based green QLEDs ranks among the highest for devices utilizing triarylamine-based HTMs. Furthermore, the operational half-lifetime of the 1-PFDBF-based QLEDs is approximate to 15 900 h at 1 000 cd m(-)2 and approximate to 1 460 000 h at 100 cd m(-)2, making a significant increase of 3 600% and 6 600%, respectively, compared to TFB-based QLEDs. These findings establish DBF incorporation as an effective strategy for enhancing HTM BDE and hole mobility, optimizing charge balance within QLEDs, and ultimately enabling high-efficiency and long-lasting QLEDs. 2025-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58944 Title: Anisotropic Dynamic Disorder of π-Stacking and Static Disorder in Organic Electron Transporting Materials with Isomorphic Crystal Structures Author(s): Lee, Chae-Won; Puc, Uros; Lee, Jeong Hyeon; Cho, Na Young; Lee, Jong Bum; Lee, Yun-Sang; Kim, Jin Chul; Yoon, Woojin; Yun, Hoseop; Jang, Seokhoon; Lee, Youngu; Kim, Jong H.; Kwak, Sang Kyu; Jazbinsek, Mojca; Kwon, O-Pil Abstract: In organic semiconductors, charge transport is strongly correlated with intermolecular π–π interactions and the dynamic disorder caused by solid-state phonon vibrations. However, for pure π–π stacking of semiconducting cores, solid-state phonon vibrations and their directional characteristics are relatively unexplored. In this work, solid-state phonon vibrations using experimental and theoretical phonon-resolved analyses of single crystals are studied, for which a series of organic electron-transporting naphthalene diimide (NDI) analogs as a model system is designed. The three NDI analogs in this series exhibit isomorphic crystal structures with a brickwork-type assembly characterized by pure face-to-face π–π stacking, but different π–π stacking distances. The as-grown NDI single crystals exhibit strong anisotropic phonon vibrations, with substantial differences observed between the directions parallel and perpendicular to the π–π stacking, appearing in two distinct THz frequency ranges (below and above 7 THz). These vibrations originate from the out-of-plane and in-plane movements of the NDI cores, respectively. For vacuum-deposited polycrystalline films, despite having isomorphic crystal structures with equivalent dominant (001) facets, the static disorder, which is influenced by crystalline perfection and trap density, varied markedly among the three NDI analogs. 2025-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58317 Title: Electronic Nose Based on a Multi-Thin Film Transistor Sensor Array Structure for Detecting Odorants with High Selectivity Author(s): Kim, Sohee; Pyo, Goeun; Choi, Wonhyuk; Jang, Hyun Woo; Kwon, Hyeokjin; Kim, Kwangsu; Heo, Su Jin; Kim, Dong Su; Kim, Jongyoun; Lee, Youngu; Kang, Hongki; Kwon, Hyuk-Jun; Moon, Cheil; Jang, Jae Eun; Kim, Sohee Abstract: Electrical noses that mimic the human olfactory system have been developed to detect odors or flavors. Unfortunately, little research on sensing reactions to various odors like a human nose can be found in the literature. Herein, an electronic nose is proposed using a multi-thin film transistor (TFT) sensor array with various polymer selectors and multi-output signal processing to detect various odorants with high selectivity. Through the combination of multi-output produced by eight polymer variables based on indium gallium zinc oxide (IGZO) TFTs, a specific radar pattern and its selectivity are generated for the eight different odor substances. Eight multi-output signal processing reduced the correlation coefficient of similarity from 77.9% to 45% relative to the case of four multi-output processing. Because the polymers have different functional groups, polymers showed specific reactions to various odorants, like the human's system, and multi-output analysis could distinguish various odors, even if polymers did not show single selectivity to a specific odor. And the sensitivity improved when compared to two-terminal structures by using TFTs based on IGZO. The advantage is that it can classify multiple odors with good selectivity and sensitivity. This sensor and signal processing concept can be applied to E-nose systems capable of odor monitoring. © 2025 Wiley-VCH GmbH. 2025-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58237 Title: Photothermally Cross-Linkable Polymeric Hole Transport Material Functionalized with Azide for High-Performance Quantum Dot Light-Emitting Diodes Author(s): Hwang, Youngjun; Jung, Hyeonwoo; Kim, Jongyoun; Park, Jaehyoung; Maheshwaran, Athithan; Kang, Byeongjae; Lee, Youngu Abstract: Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4 '-(N-(4-butylphenyl)))] (TFB) is a widely used hole transport material (HTM) in quantum dot light-emitting diodes (QLEDs). However, TFB-based solution-processed QLEDs face several challenges, including interlayer erosion, low hole mobility, shallow energy level of the highest occupied molecular orbital, and current leakage, which compromise the device efficiency and stability. To overcome these challenges, bromine and azide-based photothermally cross-linkable TFB derivatives, i.e., TFB-Br and TFB-N3, were designed and synthesized. TFB-N3 photothermally cross-linked under 254 nm ultraviolet light at 140 degrees C exhibited excellent solvent resistance within 30 s. Furthermore, the photothermally cross-linked TFB-N3 formed a compact three-dimensional (3D) network in QLEDs, enhancing hole transport and reducing the leakage current. Moreover, the HOMO energy level in photothermally cross-linked TFB-N3 decreased to -5.39 eV from that in TFB (-5.30 eV), reducing the hole transport energy barrier. Thus, the charge balance in the quantum dot (QD) layer was enhanced, and the current leakage was reduced, improving the overall QLED performance. The photothermally cross-linked TFB-N3-based QLEDs achieved a maximum external quantum efficiency of 19.53%, i.e., 61% higher than that of devices using TFB. Moreover, the T 90 lifetime of the photothermally cross-linked TFB-N3-based QLEDs was 4.49 times longer than that of TFB-based devices. The proposed strategy demonstrates that incorporating azide groups into polymeric HTMs can considerably enhance their hole transport and solvent resistance and reduce leakage current, improving QLED efficiency and stability. 2024-12-31T15:00:00Z