• Current Photovoltaic Research
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• v.7 no.4
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• pp.97-102
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• 2019

Bifacial and semitransparent hydrogenated amorphous silicon (a-Si:H) thin-film solar cells in p-i-n configuration were prepared with front and rear transparent conducting oxide (TCO) electrodes using plasma-enhanced chemical vapor deposition method. Fluorine-doped tin oxide and tin-doped indium oxide films were used as front and rear TCO contacts, respectively. Film thickness of intrinsic a-Si:H absorber layers were controlled from 150 nm to 450 nm by changing deposition time. The dependence of performance characteristics of solar cells on the front and rear illumination direction were investigated. For front illumination, gradual increase in the short-circuit current density (J_SC) from 10.59 mA/㎠ to 14.19 mA/㎠ was obtained, whereas slight decreases from 0.83 V to 0.81 V for the open-circuit voltage (V_OC) and from 68.43% to 65.75% for fill factor (FF) were observed. The average optical transmittance in the wavelength region of 380 ~ 780 nm of the solar cells decreased gradually from 22.76% to 15.67% as the absorber thickness was changed from 150 nm to 450 nm. In case of the solar cells under rear illumination condition, the J_SC increased from 10.81 to 12.64 mA/㎠ and the FF deceased from 66.63% to 61.85%, while the V_OC values were maintained at 0.80 V with increasing the absorber thickness from 150 nm to 450 nm. By optimizing the deposition parameters, a high-quality bifacial and semitransparent a-Si:H solar cell with 350 nm-thick i-a-Si:H absorber layer exhibited the conversion efficiencies of 7.69% for front illumination and 6.40% for rear illumination, and average visible optical transmittance of 17.20%.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.463-463
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• 2014

Dye-sensitized solar cells (DSSCs) have generated a strong interest in the development of solid-state devices owing to their low cost and simple preparation procedures. Effort has been devoted to the study of electrolytes that allow light-to-electrical power conversion for DSSC applications. Several attempts have been made to substitute the liquid electrolyte in the original solar cells by using (2,2',7,7'-tetrakis (N,N-di-p-methoxyphenylamine)-9-9'-spirobi-fluorene (spiro-OMeTAD) that act as hole conductor [1]. Although efficiencies above 3% have been reached by several groups, here the major challenging is limited photoelectrode thickness ($2{\mu}m$), which is very low due to electron diffusion length (Ln) for spiro-OMeTAD ($4.4{\mu}m$) [2]. In principle, the $TiO_2$ layer can be thicker than had been thought previously. This has important implications for the design of high-efficiency solid-state DSSCs. In the present study, we have fabricated 3-D Transparent Conducting Oxide (TCO) by growing tin-doped indium oxide (ITO) nanowire (NWs) arrays via a vapor transport method [3] and mesoporous $TiO_2$ nanoparticle (NP)-based photoelectrodes were prepared using doctor blade method. Finally optimized light-harvesting solid-state DSSCs is made using 3-D TCO where electron life time is controlled the recombination rate through fast charge collection and also ITO NWs length can be controlled in the range of over $2{\mu}m$ and has been characterized using field emission scanning electron microscopy (FE-SEM). Structural analyses by high-resolution transmission electron microscopy (HRTEM) and X-Ray diffraction (XRD) results reveal that the ITO NWs formed single crystal oriented [100] direction. Also to compare the charge collection properties of conventional NPs based solid-state DSSCs with ITO NWs based solid-state DSSCs, we have studied intensity modulated photovoltage spectroscopy (IMVS), intensity modulated photocurrent spectroscopy (IMPS) and transient open circuit voltages. As a result, above $4{\mu}m$ thick ITO NWs based photoelectrodes with Z907 dye shown the best performing device, exhibiting a short-circuit current density of 7.21 mA cm-2 under simulated solar emission of 100 mW cm-2 associated with an overall power conversion efficiency of 2.80 %. Finally, we achieved the efficiency of 7.5% by applying a CH3NH3PbI3 perovskite sensitizer.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.456-461
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• 2010

We investigated the In-based ohmic contacts on Nitrogen-face (N-face) n-type GaN, as well as Ga-face n-type GaN, for InGaN-based vertical Light Emitting Diodes (LEDs). For this purpose, we fabricated Circular Transfer Length Method (CTLM) patterns on the N-face n-GaN that were prepared by using a laser-lift off method, as well as on the Ga-face n-GaN that were prepared by using a dry etching method. Then, In/transparent conducting oxide (TCO) and In/TiW schemes were deposited on the CTLM in order for low resistance ohmic contacts to form. The In/TCO scheme on the Ga-face n-GaN showed high specific contact resistance, while the minimum specific contact resistance was only 3${\times}$10$^{-2}$ $\Omega$-cm$^{2}$ after annealing at 300${^{\circ}C}$, which can be attributed to the high sheet resistance of the TCO layer. In contrast, the In/TiW scheme on the Ga-face n-GaN produced low specific contact resistance of 2.1${\times}$10$^{5}$ $\Omega$-cm$^{2}$ after annealing at 500${^{\circ}C}$ for 1 min. In addition, the In/TiW scheme on the N-face n-GaN also resulted in a low specific contact resistance of 2.2${\times}$10$^{-4}$ $\Omega$-cm$^{2}$ after annealing at 300${^{\circ}C}$. These results suggest that both the Ga-face n-GaN and N-face n-GaN.

• Journal of the Korean Chemical Society
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• v.66 no.3
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• pp.209-217
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• 2022

We have developed photosensitive electrochromic smart windows that does not require any transparent conducting oxide (TCO) substrate. In our previous study, we demonstrated that a flexible film-type device made with a low temperature curing WO₃ sol and TiO₂ sol could show a reversible and rapid switching between colored and bleached state via incorporation of platinum catalysts on the surface of WO₃ layer. However, when these devices were exposed to sunlight over 4 hour, it was confirmed that they did not return to fully bleached state in the darkened state due to their overcoloring process. In this study, we added 4-hydroxy-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPOL) as an additive to the electrolyte of photosensitive electrochromic device to effectively prevent the undesired overcoloring process. The resulting device with TEMPOL indeed did not undergo excessive coloration and showed great reversibility even after being exposed to sunlight for over 4 hours. Various concentrations of TEMPOL were applied to compare changes in the visible transmittance and coloring/bleaching kinetics of devices. In terms of energetic point of view, we proposed a plausible mechanism of TEMPOL to prevent excessive coloration.