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Role of ITO nanoparticles embedded into electrospun ITO nanofibers
Yoon, Sangcheol,Kim, Hyebin,Cha, Seung-Jae,Shin, Eun-Sol,Noh, Yong-Young,Hong, Sung-Jei,Park, Byoungchoo,Hwang, Inchan IOP 2017 Journal of Physics. D, Applied Physics Vol.50 No.47
<P>Both crystallization and molecular density are significant to achieve high electrical conductivity of transparent electrodes. Herein, we investigated the embedding effects of indium tin oxide (ITO) nanoparticles (NPs) into ITO nanofibers (NFs) synthesized by utilizing an electrospinning technique from ITO precursor solutions. We found that the ITO NPs might act as nucleation seeds that initiate crystallization of ITO, evidenced by flake-like morphologies which cannot be observed without ITO NPs. XRD measurements reveal that the ITO is crystalline with a higher degree and the size of ITO crystallites increases in the presence of ITO NPs embedded into NFs. Embedding ITO NPs leads to the formation of short fibers, but there is still large space between fibers as they are vertically stacked in the films, resulting in low electrical conductivity. Interestingly, a high ratio of ITO NPs enhances the electrical conductivity, as compared to a low ratio, which we attribute to the high fiber density on substrates due to the formation of shorter ITO NFs. Our results highlight that the ITO NPs influence not only the ITO crystallization but also the lengths of NFs. High electrical conductivity of NF films can be obtained by a high degree of crystallization and the optimum NF length that reduces spaces between NFs in the films.</P>
Implementation of active-type Lamina 3D display system.
Yoon, Sangcheol,Baek, Hogil,Min, Sung-Wook,Park, Soon-Gi,Park, Min-Kyu,Yoo, Seong-Hyeon,Kim, Hak-Rin,Lee, Byoungho Optical Society of America 2015 Optics express Vol.23 No.12
<P>Lamina 3D display is a new type of multi-layer 3D display, which utilizes the polarization state as a new dimension of depth information. Lamina 3D display system has advanced properties - to reduce the data amount representing 3D image, to be easily made using the conventional projectors, and to have a potential being applied to the many applications. However, the system might have some limitations in depth range and viewing angle due to the properties of the expressive volume components. In this paper, we propose the volume using the layers of switchable diffusers to implement the active-type Lamina 3D display system. Because the diffusing rate of the layers has no relation with the polarization state, the polarizer wheel is applied to the proposed system in purpose of making the sectioned image synchronized with the diffusing layer at the designated location. The imaging volume of the proposed system consists of five layers of polymer dispersed liquid crystal and the total size of the implemented volume is 24x18x12 mm<sup>3</sup>(3). The proposed system can achieve the improvements of viewing qualities such as enhanced depth expression and widened viewing angle.</P>
Probing Molecular Orientation of P3HT Nanofibers in Fiber-Based Organic Solar Cells
Sangcheol Yoon,Yaeeun Han,황인찬 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.1
Molecular orientation of conjugated polymers plays a key role inexciton generation/separation and charge transport, and thus significantlyinfluence photovoltaic devices. Herein, we fabricated fiber-basedorganic solar cells and investigated the photovoltaic parameters withdifferent diameters of fibers and PCBM diffusion. The open-circuitvoltage that varies with molecular orientation whether it is face-on oredge-on was observed to differ. The investigation of the open-circuitvoltage dependence reveals that thick fibers have core/shell likestructures with different orientations. Thick fibers have face-on in thecore and edge-on orientations in the shell. The face-on orientations arenot preferentially formed in thin fibers, but the PCBM diffusion caninduce face-on orientations that exist within the intermixed phase. Ourresults may shed a light on better understanding on fiber-based solarcells and suggest a way toward improving photovoltaic efficiency.
Yoon, Sangcheol,Kim, Hyebin,Shin, Eul-Yong,Bae, In-Gon,Park, Byoungchoo,Noh, Yong-Young,Hwang, Inchan Elsevier 2016 ORGANIC ELECTRONICS Vol.32 No.-
<P><B>Abstract</B></P> <P>The selection of materials for use of a hole transport layer is crucial to improve the photovoltaic performances by means of efficient hole extraction. Herein, we investigate how the formation of a hybrid dual hole transport interlayer consisting of copper (I) iodide (CuI) and molybdenum oxide (MoO<SUB>3</SUB>) affects the efficiency of the device based on poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends. The rough surface of a CuI layer was observed when prepared on indium tin oxide (ITO) substrates, but became smooth by the thermal evaporation of MoO<SUB>3</SUB> on the rough CuI surface, forming a dual layer. The devices incorporated with the layer show an enhancement in efficiency compared to the devices with the CuI or MoO<SUB>3</SUB> alone layer, which is attributed to enhanced hole extraction. Our X-ray photoelectron spectroscopy (XPS) results show that Mo<SUP>5+</SUP> defect states are increased by the interaction between MoO<SUB>3</SUB> and CuI at the interface, giving rise to an increase in gap states, which we attribute to the improvement of hole extraction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The contact of a buffer layer with the active layer has to be homogeneous. </LI> <LI> The rough CuI surface can become smooth by thermally evaporated MoO<SUB>3</SUB>. </LI> <LI> Substoichiometric MoO<SUB>x</SUB> was placed more in the region near the interface with CuI. </LI> <LI> The fine mix of CuI and MoO<SUB>3</SUB> enhances hole extraction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Yoon, Sangcheol,Kim, Hyebin,Shin, Eun-Sol,Huh, Jun Nyeong,Noh, Yong-Young,Park, Byoungchoo,Hwang, Inchan American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.39
<P>High electrical conductivity of metal oxide thin films needs uniform surface coverage, which has been the issue for the thin films based on electrospun nanofibers (NFs) that have advantage over the sputtered/spin-coated films with respect to large surface area and mechanical flexibility. Herein, we investigated a reduction in the sheet resistance of electrospun indium tin oxide (ITO) NF films with improved surface coverage. We found that the surface coverage depends significantly on the electrospinnable polymer concentration in the precursor solutions, especially after post-hot-plate annealing following the infrared radiation furnace treatment. The postannealing process increases crystallinity and oxygen vacancies. However, with a higher PVP content, it makes the surface of ITO NFs more prominently rough as a result of the formation of larger sphere-shaped ITO particles on the NF surface, which gives rise to poor surface coverage. A less poly(vinylpyrrolidone) (PVP) content in ITO NF films by eletrospinning for short deposition times was found to improve surface coverage even after postannealing. The sheet resistance notably decreases, down to as low as 850 Omega/sq, with a high transmittance of over 90%. Our study provides an understanding on how to achieve high electrical conductivity of ITO NF films with high surface coverage, which can be utilized for the optoelectronic and sensing applications.</P>
Yoon, Sangcheol,Ji, Siyoung,Yoo, Youngjun,Jeong, Ji-Eun,Kim, Jeongho,Woo, Han Young,Park, Byoungchoo,Hwang, Inchan American Chemical Society 2016 The journal of physical chemistry. B, Condensed ma Vol.120 No.50
<P>Polarized emission that is beneficial to lighting and display applications can be demonstrated by aligning emissive chromophores, which can be achieved using an electrospinning technique. We investigate the photophysical properties of nanofibers based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]/poly(ethylene oxide) blends both with and without postsolvent treatments. Two different solvents were sequentially used in an attempt to extract the insulating electrospinnable polymer and increase the polarization ratio of the nanofiber meshes by molecular reorganization. The polarization ratio of emission from the nanofiber meshes treated with N,N-dimethylformamide (DMF) following treatment with acetonitrile solvents was found to be increased. An increase in the O-O emission vibronic intensity relative to that of the O-1 peak and a reduction in the photoluminescence (PL) bandwidth were found. In addition, the PL decays faster and the parallel component along the nanofiber axis increases after the DMF treatment, indicating that the radiative recombination process becomes faster. Our results consistently show that postsolvent treatment promotes stronger J-aggregate character, with longer coherence lengths of the exciton along the long axis of the nanofibers, due to enhanced intrachain order.</P>
Sangcheol Yoon,황인찬 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.1
We numerically investigated space-charge effects in organic solar cells generatingphotocurrent with a low charge dissociation probability, using a drift-diffusionmodel with the Onsager-Braun model. In contrast to the knowledge that spacechargeeffects decrease the photocurrent efficiency, we found that under certaincircumstances, the efficiency can be enhanced by the space-charge effects. It isattributed to the increase of the charge dissociation probability spatially averaged inthe active layer. Space-charge effects become more significant when mobilities areunbalanced leading to more enhancement in photocurrent efficiency.
윤상철 ( Yoon Sangcheol ),안호원 ( An Howon ),안택원 ( Ahn Taekwon ),최해성 ( Choi Haesung ),이병권 ( Lee Byoungkwon ),서동권 ( Seo Dongkwon ),이규환 ( Lee Kyuhwan ),정상우 ( Jung Sangwoo ),이재훈 ( Yi Jaehoon ) 대한통합의학회 2020 대한통합의학회지 Vol.8 No.3
Purpose : Conventional Balance Measurement can only measure the center of gravity and the shaking movement of the body. As a result, it has the disadvantages of not responding to visual changes and blocking functions of variables. This study was carried out to evaluate the performance of new equipment that measures the balance of the body using changes in body segment and pressure using the acceleration sensor to compensate for the disadvantages of the existing equipment. Methods : To this end, balance ability was measured in 43 healthy male/female adults without orthopedic injuries and nervous system damage in the last 6 months. in a situation where the visual information was restricted by Virtual Reality (VR) gear, all subjects measured and evaluated the balance ability utilizing the new equipment. Balance measurement (Prime Medilab, Korea) and Wii fit (Nintendo, Japan) were used to measure the balance ability of the subjects, and the balance ability test was performed in 4 postures using each device for data acquisition. The test duration for each posture was 30 seconds. For data acquisition, the average value of three experiments measured using each equipment was analyzed, and the statistical test was performed using the independent sample and the corresponding sample t-test, and the significance level was set to α=.05. Results : As a result of measuring the balance ability using individual equipment, blocking visual information using VR gear, the average speed, maximum speed, and moving area of the COP increased equally. It was found that the obtained absolute size of the result in Wii was somewhat larger than that of BM. Conclusion : It is considered that in the future research, it is necessary to measure changes in the body’s center of gravity through image analysis, etc., to make clear comparison and evaluation of the usability.