https://scholar.dgist.ac.kr/handle/20.500.11750/13619 2026-10-27T09:12:14Z https://scholar.dgist.ac.kr/handle/20.500.11750/60999 Title: Excited-State Modulation by Sparse Acceptor Sites in Donor-Rich Linear Conjugated Polymer Nanoparticles for Photocatalytic Hydrogen Evolution Author(s): Kim, Sowon; Kim, Jongho; Lee, Jaeyong; Ham, Gayoung; Nam, Jaedoo; Lee, Soyeon; Yang, Jiwoong; Lee, Taek Seung; Cha, Hyojung Abstract: Donor-rich conjugated polymers are attractive photocatalysts owing to their strong light-harvesting capability, synthetic accessibility, and excellent processability. However, their photocatalytic performance is often limited by rapid excited-state relaxation and charge recombination. Here, we demonstrate a sparse acceptor strategy for regulating excited-state dynamics in donor-rich linear conjugated polymer nanoparticles. An alkoxy-poly(p-phenylene)-based polymer (PP) is modified with approximately 2 mol % benzothiadiazole (BT), thiophene-linked benzothiadiazole (DTBT), or thiophene-linked benzoselenadiazole (DTBSe) units and subsequently processed into aqueous nanoparticles through nanoprecipitation. Although all polymers retained donor-rich optical characteristics, sparse acceptor incorporation significantly influenced excited-state behavior. In particular, PP-DTBT exhibited spectroscopic signatures consistent with acceptor-mediated excited-state relaxation, prolonged photoluminescence lifetimes, and enhanced populations of long-lived photoexcited species. Transient spectroscopic analyses further revealed acceptor-mediated excited-state stabilization and Pt-mediated charge extraction under photocatalytic conditions. These characteristics were reflected in the photocatalytic performance, with PP-DTBT showing the highest hydrogen evolution activity of 1.2 mmol g-1 h-1, substantially outperforming the BT- and DTBSe-containing analogues. The results demonstrate that sparse acceptor incorporation can effectively regulate excited-state relaxation, generate long-lived excited states, and promote more favorable charge extraction and utilization pathways without disrupting the donor-rich nature of the polymer backbone. This work establishes sparse acceptor-site engineering as an effective strategy for controlling excited-state dynamics and enhancing photocatalytic hydrogen evolution in donor-rich polymer nanoparticles. 2026-09-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60995 Title: Decoupling Transparency and Electron Injection in Ultrathin Ag Electrodes Using an Al/MoO3 Double Seed Layer for Transparent Quantum Dot Light-Emitting Diodes Author(s): Bae, Yeyun; Lee, Kyoungeun; Lee, Kyunghoon; Lee, Jaeyeop; Oh, Jiyoon; Yang, Jiwoong; Kim, Chansu; Roh, Jeongkyun Abstract: There is growing interest in transparent quantum dot light-emitting diodes (Tr-QLEDs) for window-type displays. For such devices, the top transparent electrode must simultaneously provide high optical transmittance, low sheet resistance, and efficient charge injection. Ultrathin Ag films are promising because of their high conductivity and transparency, but they tend to grow via the Volmer-Weber mode, resulting in poor continuity and increased resistance. Although seed layers have been widely used to improve Ag film continuity, their influence on charge injection in practical devices has received limited attention. Here, an Al/MoO3 double seed layer is introduced, in which MoO3 provides high transmittance and low sheet resistance, while Al enhances electron injection. This strategy enables continuous 10 nm Ag films with a transmittance of 63.48% and a sheet resistance of 7.35 Omega sq-1. Tr-QLEDs incorporating the Al/MoO3 double seed layer exhibit a twofold increase in external quantum efficiency and a threefold improvement in operational lifetime compared with devices employing a MoO3 single seed layer. Furthermore, large-area Tr-QLEDs are demonstrated on a 2 & times; 2 inch substrate, highlighting the potential of this electrode strategy for scalable transparent displays. 2026-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60988 Title: Composition-driven anion vacancy control in I–III–VI CuIn(S1−xSex)2 quantum dots for efficient photoelectrochemical hydrogen production Author(s): Kim, Kiwook; Kim, Hwapyong; Ha, Seung Beom; Chung, Wookjin; Lee, Hyo Cheol; Park, Soo Ik; Kim, Minseo; Li, Shi; Lee, Kyunghoon; Lee, Gyudong; Lee, Orim; Ji, Seunghyun; Ma, Hyeonjong; Lim, Sung Jun; Choi, Hongsoo; Ko, Seo-Jin; Kim, In Young; Kim, Jae-Yup; In, Su-Il; Yang, Jiwoong Abstract: Heavy-metal-free I–III–VI quantum dots (QDs) are promising candidates for solar energy conversion owing to their strong light absorption, broadly tunable bandgap spanning the full solar spectrum, and environmentally benign composition. However, precise control over their composition and defect states remains challenging due to their complex multinary synthesis chemistry, which critically governs their optoelectronic properties. Here, we demonstrate composition-driven control of anion vacancies in p -type CuIn(S1− x Se x )2 QDs and elucidate their impact on photoelectrochemical (PEC) hydrogen production. Systematic variation of the chalcogenide S/Se ratio enables modulation of anion vacancy concentrations without altering QD size or Cu/In stoichiometry. Notably, CuIn(S0.5Se0.5)2 QDs exhibit the lowest density of anion vacancies, attributed to enhanced anion coordination and reduced lattice distortion. These structural improvements result in increased hole concentration and extended carrier lifetimes. As a result, when integrated into TiO2-based photoanodes, these QDs deliver a high photocurrent density of 15.1 mA cm−2 at 0.6 VRHE for PEC hydrogen generation, exceeding the performance of most previously reported heavy-metal-free QD-based systems. This work provides fundamental mechanistic insights into the role of anion vacancies in I–III–VI QDs and offers a promising strategy for advancing their PEC performance. © 2025 The Authors. 2026-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60880 Title: Site-specific fluorination on donor-acceptor polymers enhances intramolecular charge transfer for photocatalytic hydrogen evolution Author(s): Jung, Wooteak; An, Sanghyeok; Ham, Gayoung; Choi, Geoneop; Lee, Soyeon; Park, Kyo Bin; Yang, Jiwoong; Chung, Dae Sung; Cha, Hyojung Abstract: The development of polymer photocatalysts remains a central challenge in achieving efficient solar-to-fuel conversion. A key limitation lies in the use of weak donor units, which hampers the optimization of intramolecular donor-acceptor interactions and reduces charge-transfer efficiency. Here, we report a site-specific fluorination strategy that addresses this bottleneck by introducing fluorine atoms at defined positions along the polymer backbone via a unique two-step polymerization protocol. Two representative random copolymers were synthesized: the acceptor-fluorinated polymer (PBF8BT-AF) and the donor-fluorinated polymer (PBF8BT-DF). Strikingly, PBF8BT-DF exhibited superior photocatalytic activity, while PBF8BT-AF showed inferior performance due to exciton loss through a non-productive decay pathway. A comprehensive spectroscopic analysis, supported by density functional theory (DFT) calculations, reveals that donor-site fluorination promotes exciton delocalization across the entire repeating unit, thereby facilitating efficient intramolecular charge transfer. In contrast, acceptor fluorination energetically localizes the excited state, impeding exciton migration and suppressing charge utilization. These findings underscore the critical role of site-specific exciton stabilization in determining photocatalytic efficiency and establish domain-targeted molecular engineering as a powerful design principle for next-generation polymer photocatalysts. 2026-06-30T15:00:00Z