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Haksoo Lee

Bio: Haksoo Lee is an academic researcher from Sungkyunkwan University. The author has contributed to research in topics: OLED & Layer (electronics). The author has an hindex of 6, co-authored 9 publications receiving 106 citations.

Papers
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Journal ArticleDOI
01 May 2017-Carbon
TL;DR: In this paper, a composite layer of atomic layer-deposition-grown Al 2 O 3 on CVD graphene was fabricated for encapsulation of an organic light-emitting diode (OLED).

40 citations

Journal ArticleDOI
16 Apr 2013-Langmuir
TL;DR: A novel cost- and time-effective vacuum-free process to fabricate bulk-heterojunction (BHJ) organic photovoltaics (OPVs) via layer-by-layer selective stamping transfer of all layers and shows the possibility of fabricating OPVs via the layer- by-layer transfer method for the first time.
Abstract: For the first time, we describe a novel cost- and time-effective vacuum-free process to fabricate bulk-heterojunction (BHJ) organic photovoltaics (OPVs) via layer-by-layer selective stamping transfer of all layers. By controlling the surface properties of polyurethane acrylate (PUA) stamping molds with ultraviolet (UV)–ozone (UVO) exposure, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), BHJ layer, and metal cathode were uniformly transferred layer by layer onto each of the bottom layers. Among several interfaces between each layer, we found that the interface between the active layer and metal cathode is a critical factor in obtaining conventional device-like efficiency. To enhance the interfacial connectivity between the BHJ layer and metal cathode and increase electron extraction from the BHJ layer, a titanium oxide (TiOx) interlayer was introduced. Cell performance was optimized by controlling the concentration of TiOx solution. The poly(3-hexylthiophene-2,5-diyl)/[6,6]-phenyl-C61...

22 citations

Journal ArticleDOI
TL;DR: In this paper, a homojunction of single-crystalline Ga2O3 nanowires and nanocrystals was realized, and it was shown that the?-Ga2O 3 nanomaterials form a single unit with the nanowire and are part of the same single crystal with a perfect lattice.
Abstract: A homojunction of single-crystalline ?-Ga2O3 nanowires and nanocrystals was realized. Ga2O3 nanowires were synthesized at about 850?950??C using a mixture of Ga2O3 and graphite powder with vapor phase epitaxy. It was found that the ?-Ga2O3 nanocrystals form a single unit with the nanowires and are part of the same single crystal with a perfect lattice. Growth of ?-Ga2O3 nanocrystals follows the growth direction of the main ?-Ga2O3 nanowires. The distance between neighboring atoms in ?-Ga2O3 nanowires was 0.522?nm, which is similar to the theoretical value for bulk ?-Ga2O3.

14 citations

Journal ArticleDOI
Se Hee Lim1, Seung-Woo Seo1, Haksoo Lee1, Heeyeop Chae1, Sung Min Cho1 
TL;DR: In this paper, an organic/inorganic multilayer structure was fabricated for extreme flexibility and enhanced moisture-barrier property, which was shown to retain the initial barrier property even after 10,000 times of bending at a radius as small as 3mm when the barrier structure was located at a neutral plane.
Abstract: Organic/inorganic multilayer structures were fabricated for extreme flexibility as well as enhanced moisturebarrier property. The organic and inorganic layers for the structures were formed by plasma polymerization and atomic layer deposition, respectively. The layers were grown alternately to form the organic/inorganic multilayer structures on a plastic substrate. To accomplish extreme flexibility of the barriers, ultra-thin aluminum oxide layers were grown by the atomic layer deposition and sandwiched by a flexible plasma-polymer layer. The moisture-barrier films were then confirmed to retain the initial barrier property even after 10,000 times of bending at a radius as small as 3mm when the barrier structure was located at a neutral plane.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of hole-transport layer thickness on deep-blue emission was experimentally and theoretically elucidated for top-emitting micro-cavity organic lightemitting diodes.
Abstract: The effect of hole-transport-layer thickness on deep-blue emission was experimentally and theoretically elucidated for top-emitting micro-cavity organic light-emitting diodes. As a result of strong optical interference in the micro-cavity, the emission spectrum and intensity from the top-emitting organic light-emitting diodes was strongly dependent on the viewing angle. Optimizing hole-transport-layer thickness lead to deep-blue emissions at a wavelength of about 460 nm with a current efficiency of 5 cd/A at 10,000 cd/m2 luminance. Light out-coupling in the top-emitting organic light-emitting diodes was modeled and calculated to show the power dissipation, and the model explained the experimental results well.

11 citations


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Journal ArticleDOI
TL;DR: In this article, the authors present an up-to-date review of metal oxide materials research for gas sensors application, due to the great research effort in the field it could not cover all the interesting works reported, the ones that, according to the authors, are going to contribute to this field's further development were selected and described.

590 citations

Journal ArticleDOI
TL;DR: In this article, a comprehensive review on Ga2O3-based solar-blind UV photodetectors is provided, with a detailed introduction of the developmental process of material growth methods and device manufacturing in the past decade.
Abstract: In recent years, solar-blind ultraviolet (UV) photodetectors have attracted significant attention from researchers in the field of semiconductor devices due to their indispensable properties in the fields of high-temperature event monitoring, anti-terrorism, security and ad hoc network communication. As an important member of the third-generation semiconductors, β-Ga2O3 is considered to be one of the most promising candidates for solar-blind UV detectors due to its ultra-wide band gap (∼4.9 eV), economic efficiency, high radiation resistance and excellent chemical and thermal stability. Herein, we provide a comprehensive review on Ga2O3-based solar-blind UV photodetectors, with a detailed introduction of the developmental process of material growth methods and device manufacturing in the past decade. We classify the currently reported Ga2O3-based solar-blind UV photodetectors (mainly including photoconductive detectors, heterogeneous PN junction detectors and Schottky junction detectors) and summarize their respective superiorities and potentials for improvement. Finally, considering the actual application requirements, we put forward some meaningful suggestions, including energy band engineering and homogeneous epitaxy, for the future development of Ga2O3 material growth and device manufacturing.

293 citations

Journal ArticleDOI
TL;DR: In this paper, a bridged β-Ga 2 O 3 nanowire-based photodetector was used for solar-blind photodeter detection, which has a high 250-to-280-nm rejection ratio, low photocurrent noise, and fast decay time.
Abstract: An increasing number of applications using ultraviolet radiation have renewed interest in ultraviolet photodetector research. Particularly, solar-blind photodetectors sensitive to only deep UV ( < 280 nm), have attracted growing attention because of their wide applicability. Among recent advances in UV detection, nanowire (NW)-based photodetectors seem promising, however, none of the reported devices possesses the required attributes for practical solar-blind photodetection, namely, an effi cient fabrication process, a high solar light rejection ratio, a low photocurrent noise, and a fast response. Herein, the assembly of β -Ga 2 O 3 NWs into high-performance solar-blind photodetectors by use of an effi cient bridging method is reported. The device is made in a single-step chemical vapor deposition process and has a high 250-to-280-nm rejection ratio ( ∼ 2 × 10 3 ), low photocurrent fl uctuation ( < 3%), and a fast decay time ( < < 20 ms). Further, variations in the synthesis parameters of the NWs induce drastic changes in the photoresponse properties, which suggest a possibility for tuning the performance of the photodetectors. The effi cient fabrication method and high performance of the bridged β -Ga 2 O 3 NW photodetectors make them highly suitable for solar-blind photodetection.

293 citations

Journal ArticleDOI
TL;DR: An organic solar cell containing double bulk heterojunction layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers to allow a large gain in photocurrent to be obtained due to enhanced photoharvest.
Abstract: An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC71 BM layer atop of ≈200 nm PTB7-Th:PC71 BM BHJ results in high power conversion efficiencies over 12%.

132 citations

Journal ArticleDOI
TL;DR: In this paper, a growth relationship between growth rates and increasing gallium fluxes was established at a fixed oxygen pressure, and a three-dimensional columnar growth with a relatively high growth rate was measured at a low gallium density, while a terrace surface morphology with a reduced growth rate increased as the gallium densities increased.
Abstract: The authors demonstrate the heteroepitaxial and homoepitaxial growth of single crystalline β-Ga2O3 by plasma-assisted molecular beam epitaxy. Phase-pure (2¯01) and (100) β-Ga2O3 thin films were grown on c-plane sapphire and (100) β-Ga2O3 substrates, respectively. Based on the homoepitaxial results, detailed information is reported on the dependence between the β-Ga2O3 film quality and various growth parameters. At an optimized growth temperature of 700 °C, a growth relationship between growth rates and increasing gallium fluxes was established at a fixed oxygen pressure. A three-dimensional columnar growth with a relatively high growth rate was measured at a low gallium flux while a terrace surface morphology with a reduced growth rate was observed as the gallium flux increased. The gallium flux played an important role on both surface morphology and growth rate. We associated the decreasing growth rate with increasing gallium flux with the formation of gallium suboxides monitored by quadrupole mass spect...

108 citations