https://scholar.dgist.ac.kr/handle/20.500.11750/13619 2026-10-03T23:14:46Z 2026-10-03T23:14:46Z Jung, Wooteak An, Sanghyeok Ham, Gayoung Choi, Geoneop Lee, Soyeon Park, Kyo Bin Yang, Jiwoong Chung, Dae Sung Cha, Hyojung https://scholar.dgist.ac.kr/handle/20.500.11750/60880 2026-09-29T02:40:14Z 2026-06-30T15:00:00Z

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 Lee, Daewon Oaks-Leaf, Sam Ma, Hyeonjong He, Jianlong Wang, Zhiqi Shi, Yifeng Ahn, Eonhyoung Bustillo, Karen C. Song, Chengyu Ribet, Stephanie M. Dhall, Rohan Ophus, Colin Asta, Mark Yang, Jiwoong Xia, Younan Limmer, David T. Zheng, Haimei https://scholar.dgist.ac.kr/handle/20.500.11750/60536 2026-07-30T08:40:12Z 2026-04-30T15:00:00Z

Title: Nanocrystal Geometry Governs Phase Transformation Pathways in Palladium Hydride Author(s): Lee, Daewon; Oaks-Leaf, Sam; Ma, Hyeonjong; He, Jianlong; Wang, Zhiqi; Shi, Yifeng; Ahn, Eonhyoung; Bustillo, Karen C.; Song, Chengyu; Ribet, Stephanie M.; Dhall, Rohan; Ophus, Colin; Asta, Mark; Yang, Jiwoong; Xia, Younan; Limmer, David T.; Zheng, Haimei Abstract: Pathways and structural dynamics of phase transformations impact performance of materials in energy and information storage technologies. Palladium hydride (PdHx ) nanocrystals are an ideal model system for studying solute-induced phase transformations, where elastic energy from lattice mismatch between alpha-PdH, and beta-PdH, phases is often considered a key to determining the transformation pathways. alpha/beta-PdHx interfacial elastic energy is affected by the confined geometry of a nanocrystal. However, how nanocrystal geometry influences phase trans-formation pathways is largely unknown. Using in situ liquid phase transmission electron microscopy, we directly visualize hydrogenation in Pd nanocrystals with two geometries, a nanocube and a hexagonal nanoplate. Both follow similar sequences of an initially curved nucleus, interface flattening, and reverse-stage nucleation; however, their evolving alpha/beta-PdHx interfaces exhibit geometry-dependent crystallographic alignments. In nanocubes, (100)-aligned configurations conform to static elastic energy ordering, representing a pathway that maintains a local mechanical equilibrium, whereas nanoplates display both (110) and (211)-aligned interfaces. Theoretical simulations show that geometry determines the accessibility of alternative phase transformation pathways as the system is driven far from equilibrium during hydrogenation. These findings identify geometry as a fundamental parameter for directing phase transformation pathways, offering design principles for accessing atypical configurations and improving properties of intercalation-based devices.

2026-04-30T15:00:00Z Kim, Minseo Li, Shi Lee, Kyunghoon Ahn, Eonhyoung Lee, Soyeon Kim, Kiwook Kim, Hang Yu, Wookyung Choi, Changsoon Lim, Jung Ah Hwang, Jeeseong Kim, Dae-Hyeong Yang, Jiwoong https://scholar.dgist.ac.kr/handle/20.500.11750/60475 2026-07-22T18:01:28Z 2026-02-28T15:00:00Z

Title: Broadband Circularly Polarized Light Detection via Spin-Selective Charge Transport in Quantum Dot Photodiodes Author(s): Kim, Minseo; Li, Shi; Lee, Kyunghoon; Ahn, Eonhyoung; Lee, Soyeon; Kim, Kiwook; Kim, Hang; Yu, Wookyung; Choi, Changsoon; Lim, Jung Ah; Hwang, Jeeseong; Kim, Dae-Hyeong; Yang, Jiwoong Abstract: Circularly polarized light (CPL) detection provides polarization-resolved information, enabling advanced applications in quantum technologies, bioimaging, secure communications, and multi-level optical data processing. However, conventional CPL photodetectors typically rely on intrinsically chiral absorbers, restricting operation to the UV-vis range and hindering extension into the near-infrared (NIR) and shortwave infrared (SWIR), which are critical for deep tissue imaging and low-visibility sensing. Here, we demonstrate broadband CPL detection with quantum dot (QD) photodiodes that exploit the chiral-induced spin selectivity effect in chiral-ZnO charge transport layers. Chiral ligand-functionalized ZnO electron transport layers selectively transmit spin-polarized charge carriers from QDs, enabling CPL-specific photocurrent generation even in spectral regions without intrinsic chiral absorption. Heavy-metal-free Cu-In-Se QD-photodiodes exhibit outstanding specific detectivity (D *) of 1.28 x 1012 Jones without external bias and broadband CPL detection (g Iph: similar to 0.17 at 260 nm and similar to 0.13 at 780 nm), while PbS QD-devices extend CPL detection across 250-1700 nm (UV-Vis-NIR-SWIR) with superior performance (D *: 1.45 x 1012 Jones). The chiral-transport-driven strategy offers fundamental insights into CPL photodetection and establishes a scalable and optically passive platform for broadband polarization-resolved optoelectronics.

2026-02-28T15:00:00Z Kim, Sowon Yu, Youngwoong Choi, Hyunwoo Ham, Gayoung An, Sanghyeok Lee, Soyeon Yang, Jiwoong Chung, Dae-sung Lee, Jihoon Cha, Hyojung https://scholar.dgist.ac.kr/handle/20.500.11750/60006 2026-02-10T18:01:16Z 2025-12-31T15:00:00Z

Title: Synergistic dual-electron acceptors in linear conjugated polymers for boosting photocatalytic hydrogen evolution Author(s): Kim, Sowon; Yu, Youngwoong; Choi, Hyunwoo; Ham, Gayoung; An, Sanghyeok; Lee, Soyeon; Yang, Jiwoong; Chung, Dae-sung; Lee, Jihoon; Cha, Hyojung Abstract: A conjugated polymer photocatalyst containing dual-electron acceptor units, dibenzo[b,d]thiophene sulfone (DBS) and 2,1,3-benzothiadiazole (BT), known as PBT, has been synthesized for its strong electron-withdrawing abilities and structural flexibility. However, the inherent hydrophobicity of PBT leads to significant particle aggregation, hindering colloidal stability and electron transfer to protons. To overcome these limitations, fluorine and ethylene glycol (EG) groups are strategically incorporated into the BT unit to enhance molecular planarity and hydrophilicity, respectively. This molecular engineering effectively suppresses exciton and charge recombination, facilitating efficient charge separation and extraction. Comprehensive spectroscopic analyses—including time-resolved photoluminescence (Tr-PL) and transient absorption spectroscopy (TAS)—reveal that EG-functionalized polymers exhibit prolonged exciton lifetimes and strong photoinduced absorption at early timescales, indicating both suppressed non-radiative recombination and effective charge generation. Importantly, these modifications enable rapid charge separation and transfer with more efficient electron extraction to protons, mitigating charge accumulation within aggregated domains. Among the modified polymers, 4EG-PBTz-F, with di-fluoro substituents and tetra-ethylene glycol groups, achieves the highest hydrogen evolution rates of 15.476 mmol g−1 and 3.095 mmol g−1 h−1 with a 3 wt% Pt co-catalyst. These results highlight the effectiveness of dual-electron acceptor design and interfacial control, offering a multi-faceted design strategy in photocatalytic hydrogen evolution systems.

2025-12-31T15:00:00Z