https://scholar.dgist.ac.kr/handle/20.500.11750/13620 2026-04-04T14:35:57Z https://scholar.dgist.ac.kr/handle/20.500.11750/57883 Title: Transformation Mechanism of Quantum-Sized Semiconductor Nanocrystals Revealed by in Situ Transmission Electron Microscopy Author(s): Yang, Jiwoong Abstract: Semiconductor nanocrystal quantum dots are renowned for their remarkable properties, including tunable bandgap, pure color emission with exceptionally narrow bandwidths, and high luminescence efficiency. A thorough understanding of the transformation mechanism of quantum-sized semiconductor nanocrystals is essential for their practical application, as their properties are determined by their structure. This presentation will focus on exploring these mechanisms using in-situ transmission electron microscopy (TEM). The first part of the talk will examine the moisture-induced degradation of quantum-sized semiconductor nanocrystals, highlighting a notable finding: the formation of amorphous intermediates on the surfaces of these nanocrystals during degradation. This insight is crucial for developing strategies to enhance the stability and durability of nanocrystals, thereby extending their practical application. Next, I will discuss the crystal phase transition mechanism in II-VI semiconductor nanocrystals, triggered by off-stoichiometry. This discussion will shed light on the determinants of the crystal phase in these nanocrystals, a key to understanding their functionality. Lastly, the presentation introduces the application of in-situ X-ray scattering. This technique offers structural insights that complement those obtained from in-situ TEM, significantly enriching our understanding of the structural dynamics in semiconductor nanocrystals. 2024-05-27T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57754 Title: Ultrathin, Self-Powered, Heavy-Metal-Free Cu-In-Se Quantum Dot Photodetectors for Wearable Healthcare Monitoring System Author(s): 장재홍; 최문기; Li, Shi; Yang, Jiwoong Abstract: Mechanically deformable photodetectors (PDs), vital for wearable health monitoring systems using photoplethysmography (PPG), require high detectivity, fast response time, self-powered operation, and an ultrathin form factor for next-generation applications. We propose ultrathin self-powered PDs using heavy-metal-free CISe quantum dots (QDs) for high-performance wearable PPG systems. Despite a thin light-absorbing QD layer (~40 nm), PD shows excellent performance with a specific detectivity of 2.10 × 10¹² Jones and a spectral range of 250-1,050 nm at zero bias. This performance is due to the strategic use of materials and design: CISe QDs, MoS₂-nanosheet-blended PEDOT:PSS hole transport layer, ZnO nanoparticle electron transport layer, Ag and ITO electrodes, and ultrathin form factor (~120 nm excluding electrodes) ensuring excellent mechanical deformability. These features enable effective QD-PDs for wearable real-time PPG monitoring, expanding their potential in mobile bioelectronics. 2024-09-29T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57751 Title: Advanced Full-Color Perovskite Nanocrystal Patterning for Next-Generation Ultrathin Skin-Attachable Displays Author(s): 김지원; 권종익; 박규리; 이광헌; 장재홍; 성낙준; 김서영; 유지수; 이경훈; 마현종; 갈민지; 신태주; 송명훈; 양지웅; 최문기 Abstract: We present a novel ultrahigh-resolution perovskite nanocrystal (PeNC) patterning technique for ultrathin wearable displays. Our method employs double-layer transfer printing to layer PeNCs and organic charge transport layers, preventing internal cracking and achieving RGB pixelated patterns at 2550 PPI and monochromatic patterns at 33,000 line pairs per inch. The resulting perovskite light-emitting diodes (PeLEDs) display exceptional electroluminescence, with quantum efficiencies significantly higher than previously reported printed PeLEDs. This technology enables the creation of flexible, multicolor PeLEDs that adhere to curvilinear surfaces, including human skin, supporting various mechanical deformations. These advancements suggest significant potential for PeLEDs in future high-definition wearable displays. 2024-09-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57750 Title: Highly Efficient Printed Quantum Dot Light-emitting Diodes through Ultrahigh-definition Double-layer Transfer Printing Author(s): 유지수; 최문기; 양지웅; 현택환; 이경훈 Abstract: Highly efficient, high-definition displays with deformable form factors are essential for next-generation electronic devices. Quantum dots (QDs) offer unique advantages such as high photoluminescence quantum yield, wide color range, and high color purity. However, developing a QD patterning process for high-definition pixels and efficient QD light-emitting diodes (QLEDs) is still nascent. We present highly efficient QLEDs via ultrahigh-definition double-layer transfer printing of a QD/ZnO film. Surface engineering of viscoelastic stamps enables creating RGB pixelated patterns with 2,565 pixels per inch and monochromatic QD patterns with ~20,526 pixels per inch. This method minimizes leakage current, enhancing external quantum efficiency to 23.3%. Additionally, we demonstrate highly efficient wearable QLEDs using our technique. This study paves the way for highly efficient, full-color QD displays through transfer printing, promising next-generation display technologies. 2024-09-30T15:00:00Z