https://scholar.dgist.ac.kr/handle/20.500.11750/58675 2026-10-25T09:02:23Z https://scholar.dgist.ac.kr/handle/20.500.11750/61010 Title: Mitigating the Trade-Off between Bandgap Narrowing and Trap-Limited Transport for Low-Noise Organic Short-Wave Infrared Photodetectors Author(s): Kwon, Ohhyun; Lee, Un-Hak; Lee, Gyeong Min; Oh, Seunghyun; Park, Se Jeong; Choi, Yeonsu; Ahn, Hyungju; Lee, Sang Heon; Rhee, Seunghyun; Whang, Dong Ryeol; Nam, SungWoo; Ko, Seo-Jin; Shim, Jae Won Abstract: Solution-processed organic photodetectors present a promising route to short-wave infrared detection; however, accessing the spectral region beyond 1200 nm requires sub-1.0 eV organic absorbers, typically achieved through strong intramolecular charge transfer, enhanced quinoidal character, and extended pi-conjugation; whereas, conformational and energetic disorder in such narrow-bandgap systems can contribute to trap-mediated transport losses and elevated dark current. This study introduces Fc2BS and Fc2BT, narrow-bandgap nonfullerene acceptors differing solely in the pi-bridge unit (benzoselenadiazole vs benzothiadiazole), to examine how chalcogen substitution influences bandgap narrowing and trap-related transport in sub-1.0 eV organic absorbers. Fc2BS achieves an optical bandgap of 0.98 eV with absorption extending to 1263 nm, where benzoselenadiazole substitution is associated with reduced structural and energetic disorder relative to benzothiadiazole. Compared to the Fc2BT-based device, the Fc2BS-based device suppresses trap density by 8-fold and extends the critical carrier transport length by an order of magnitude, mitigating the dark current-responsivity trade-off and achieving a dark current density of 7.88 & times; 10-9 A cm-2 with an EQE of 12.5% at 1200 nm even at a low bias of -0.1 V, while enabling stable low-bias operation through suppressed bias-dependent collection bottlenecks and dark current drift. A directly measured noise equivalent power of 2.14 pW and corresponding specific detectivity of 1.47 & times; 1011 cm & centerdot;Hz1/2 & centerdot;W-1 at 1200 nm highlight the benzoselenadiazole pi-bridge as a promising molecular-design motif for extending SWIR response while limiting noise and transport penalties. 2026-09-30T15:00:00Z 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/20.500.11750/60878 Title: Structure-Controlled Cyclopentadithiophene Derived Non-Fullerene Acceptors for Efficient Near-Infrared Organic Photodetectors Author(s): Ha, Jong-Woon; Kim, Jae-Hyun; Park, Byoungwook; Park, Honghyun; Yoon, Sung Cheol; Jeong, Jaebin; Lee, Seunghun; Park, Jaeil; Choi, Jun-Gyu; Ko, Seo-Jin; Lee, Seung-Hoon; Park, Sungjun Abstract: High-performance near-infrared (NIR) organic photodetectors are still limited by insufficient absorption beyond 900 nm and the concomitant increase in dark current and noise. Here, we present organic photodetectors based on novel low-bandgap non-fullerene acceptors (NFAs), OC and SC, designed via a molecular strategy that introduces dithieno[3,2-b:2 ',3 '-d]pyran (DTP) and dithieno[3,2-b:2 ',3 '-d]thiopyran (DTTP) as central cores. The resulting PTB7-Th:OC organic photodiodes (OPDs) exhibit well-minimized dark-current densities (similar to 10-8 A cm-2) under a reverse bias of -2 V and maintain high spectral responsivities across the short-NIR region, reaching 0.4 A W-1 around 900 nm and remaining appreciable up to 1000 nm, leading to an excellent shot-noise-limited specific detectivity exhibiting 2.34 & times; 1012 Jones. Furthermore, the practical applicability of PTB7-Th:OC-based OPDs is demonstrated in a NIR photoplethysmogram sensor, which delivers stable and clearly resolved signals. Overall, this work highlights DTP/DTTP-based NFAs as promising materials for high-performance NIR-responsive OPDs and provides useful design guidelines for future NIR photodetection applications. 2026-07-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59966 Title: Ultra-Sensitive Short-Wave Infrared Organic Photodetectors Enabled by a π-Conjugation Extended Proquinoid Electron Acceptor Author(s): Choi, Yeonsu; Park, Se Jeong; Oh, Seunghyun; Lee, Un-Hak; Rhee, Seunghyun; Whang, Dong Ryeol; Chung, Sein; Jung, Juhyoung; Cho, Kilwon; Lee, Bo Ram; Yoon, Sung Cheol; Shim, Jae Won; Ko, Seo-Jin Abstract: Short-wavelength infrared (SWIR) light detection technologies have attracted considerable attention due to their broad applications in bioimaging, sensing, and optical communication. Despite this promise, achieving high-performance organic SWIR photodetectors (SWIR OPDs) remains a major challenge due to intrinsically weak photoresponse and sensitivity in this spectral region. Herein, a novel proquinoid-type non-fullerene acceptor (NFA), denoted as TQC-4Cl is reported, which exhibits an ultra-narrow band gap of 1.01 eV and a broad spectral response extending beyond 1200 nm, enabled via an aromatic-quinoid transformation strategy. Thermal annealing of the TQC-4Cl film significantly enhanced crystallinity and molecular ordering. Consequently, the optimized TQC-4Cl-based SWIR OPDs exhibit an exceptionally low dark current density (J d) of 4.38 x 10-8 A cm-2 , noise current of 466 fA (at 4 Hz), and a high external quantum efficiency (EQE) of 13.66% at 1200 nm at -0.5 V bias, resulting in a shot-noise limited specific detectivity (Dsh*) of 1.06 x 1012 Jones and a noise current-based specific detectivity (Dn*) of 2.84 x 1011 Jones under the same bias conditions. The ideal phase-separated morphology and high crystallinity of the photoactive layer provide the beneficial condition enabling efficient charge extraction, suppressed bimolecular recombination, and reduced energetic disorder. Furthermore, the devices demonstrated long-term operational stability at 85 degrees C, underscoring their superior thermal durability. This study not only marks the advancement toward the realization of highly sensitive and thermally robust SWIR OPDs but also contributes to the rational molecular design strategies for ultra-narrow bandgap organic semiconductors for next-generation optoelectronic devices. 2025-12-31T15:00:00Z