• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.276.2-276.2
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• 2016

Dye-sensitized solar cells (DSCs) are promising candidates for light-to-energy conversion devices due to their low-cost, easy fabrication and relative high conversion efficiency. An important component of DSCs is counter electrode (CE) collect electrons from external circuit and reduct I3- to I-. The conventional CEs are thermally decomposed Pt on fluorine-doped tin oxide (FTO) glass substrates, which have shown excellent performance and stability. However, Pt is not suitable in terms of cost effect. In this report, we demonstrated that nickel sulfide thin films by atomic layer deposition (ALD)-using Nickel(1-dimethylamino-2-methyl-2-butanolate)2 and hydrogen sulfide at low temperatures of $90-200^{\circ}C$-could be good CEs in DSCs. Notably, ALD allows the thin films to grow with good reproducibility, precise thickness control and excellent conformality at the angstrom or monolayer level. The nickel sulfide films were characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction, hall measurements and cyclic voltammetry. The ALD grown nickel sulfide thin films showed high catalytic activity for the reduction of I3- to I- in DSC. The DSCs with the ALD-grown nickel sulfide thin films as CEs showed the solar cell efficiency of 7.12% which is comparable to that of the DSC with conventional Pt coated counter electrode (7.63%).

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.161.1-161.1
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• 2016

박막 태양전지의 광 산란을 위한 텍스쳐 된 표면은 반사 손실을 감소시키기 위한 것이다. 그러나, 투명한 전극(TCO)의 텍스쳐 된 표면은 빛의 가용성을 제한하고, 장파장 영역에서 haze의 수치를 감소시키며, 전반사의 증가는 박막 태양전지의 Jsc를 감소시킨다. 본 논문에서는 높은 빛의 가용성을 위하여 HF+HCl 혼합용액을 이용하여 표면의 질을 향상시키기 위한 해결책을 제시했다. 같은 HF+HCl 혼합용액을 사용하여, 540 nm의 파장에서 약 85 %의 높은 haze 수치를 달성했으며, ZnO:Al 막의 증착 후에 식각된 유리 기판과 함께 비교했을 때, 2.3%의 haze 수치의 감소를 얻었다. 또, 깊은 습식 식각에 의하여 Haze 수치를 증가시키기 위한 메커니즘 간단히 설명했다. 텍스쳐 된 유리 기판의 haze 수치의 측면에서 광학 이득은 일반적인 Asahi FTO 유리(${\lambda}=540nm$의 13.5%)에 비해 상당히 높다. 이러한 높은 haze 수치의 AZO 박막은 박막 태양전지의 Jsc를 개선하는데 이용할 수 있다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2119_2120
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• 2009

전압을 인가하였을 때 전계방향에 의해 가역적으로 색이 변화하는 현상을 전기변색(electrochromism)이라고 한다. 이러한 전기채색현상을 보이는 물질을 전기채색물질(electrochromism materials)이라고 하며, 전기채색 물질에 의한 소자를 전기채색소자(electrochromism device : ECD)라고 한다. 전기채색현상은 투과율(transmittance), 반사율(reflectance)의 가역적이며 가시적인 변화이고, 전기화학적인 산화환원 반응과 관련이 있다. 따라서 본 연구에서는 Titanate nanotube(TNT)를 제조하고 전기변색소자(ECD)에 응용하였다. SEM, XRD, UV-Vis등을 이용하여 재료학적 분석을 시행하였으며, 전기화학적 테스트로 cyclic voltammetry를 측정 하였다. 그 결과 TNT 분말은 직경 약 20~30 nm, 길이 약 500~600 nm 의 입자형상을 나타내었으며, X-선 회절시험결과 $H_2Ti_2O_5{\cdot}H_2O$의 층상구조를 나타내었다. 제조된 막은 FTO glass 위에 PEI/(TNT/TBAOH)$_{n-1}$/PDDA의 순으로 코팅되었다. 전기화학적 테스트를 위하여 2전극 시스템을 제작하였으며, 여러 종류의 액체 전해질을 제작하여 cycle voltammetry를 시행하였다. 그 결과, 각각의 전해질에서 "-"영역의 산화환원전위 피크가 뚜렷하게 나타났으며, 짙은 갈색으로의 채색현상을 나타냈다. 본 연구의 결과로서 TNT 박막을 이용한 ECD은 광조절 유리로서 뿐만 아니라, 여러 전기채색 디바이스에 응용될 것으로 사료된다.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.925-928
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• 2014

A dye-sensitized solar cell (DSSC) was fabricated with a nanocrystalline $TiO_2$ film electrode on FTO glass, N719 dye, electrolytes (or $CsSnI_3$), and counter Pt electrode by incorporating it with single-walled carbon nanotubes (SWNTs). SWNTs were combined with $TiO_2$ film, $CsSnI_3$, Pt electrode, separately, and the SWNT-containing cell was compared with a pristine cell in cell performance. We also examined the performance change by pressing $TiO_2$ film, during cell fabrication, inside a high pressure chamber. Mostly, the change of conversion efficiency was compared for each cell, and an atomic force microscopy data were suggested to explain our results.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.4
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• pp.139-143
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• 2005

For application of carbon nano-tube (CNT) as a counter electrode materials of dye-sensitized solar cell (DSSC), the electrochemical behavior of CNT electrode was studied, employing cyclic-voltammetry (C-V) and impedance spectroscopy. Fabrication of CNT-paste and formation of CNT-counter electrode for characteristic measurement have been carried out using ball-milling and doctor blade process, respectively. Unit cell for measurements was assembled using Pt electrode, CNT electrode, and iodine-embedded electrolyte. Field emission-scanning electron microscopy (FE-SEM) was used for structural investigation of CNT powder and electrode. Sheet resistance of electrode was measured with 4-point probe method. Electrochemical properties of electrode, C-V and impedance spectrum, were studied, employing potentiogalvanostat (EG&G 273A) and lock in amplifier (EG&G 5210). As a results, the sheet resistance of CNT electrode is almost similar to that of F-doped SnO2 (FTO) coated glass substrate as approximately 10 ohm/sq. From C-V and impedance spectroscopy measurements, it was found that CNT electrode has high reaction rate and low interface reaction resistance between CNT surface and electrolyte. These results provides that CNT electrode were superior to that of conventional Pt electrode. Particularly, the reaction rate in the CNT electrode is about thrice high than Pt electrode. Therefore. CNT electrode is to be good candidate material for counter electrode in DSSC.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.4
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• pp.329-334
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• 2016

Hydrogen is eco-friendly alternative energy source and the photoelectrochemical water splitting is believed to be one of the promising methods for hydrogen production. Many researchers have studied several potential photocatalysts to increase the photoelectochemical performance efficiency for hydrogen conversion. In this study, the GO (graphene oxide) was prepared by Tour's method and was dispersed in precursor solutions of $WO_3$ and $BiVO_4$. Those precursor solutions were spin-coated on FTO glass and several photocatalyst thin films of $WO_3$, $BiVO_4$ and $WO_3/BiVO_4$ were prepared by calcination. The morphologies of prepared photocatalyst thin films were measured by scanning electron microscope. The photoelectrochemical performances of photocatalyst thin films with rGO (reduced graphene oxide) and without rGO were analyzed systematically.

• Korean Journal of Materials Research
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• v.30 no.9
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• pp.441-446
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• 2020

Synthesizing nanostructured thin films of oxide semiconductors is a promising approach to fabricate highly efficient photoelectrodes for hydrogen production via photoelectrochemical (PEC) water splitting. In this work, we investigate the feasibility as an efficient photoanode for PEC water oxidation of zinc oxide (ZnO) nanostructured thin films synthesized via a simple method combined with sputtering Zn metallic films on a fluorine-doped tin oxide (FTO) coated glass substrate and subsequent thermal oxidation of the sputtered Zn metallic films in dry air. Characterization of the structural, optical, and PEC properties of the ZnO nanostructured thin film synthesized at varying Zn sputtering powers reveals that we can obtain an optimum ZnO nanostructured thin film as PEC photoanode at a sputtering power of 40 W. The photocurrent density and optimal photocurrent conversion efficiency for the optimum ZnO nanostructured thin film photoanode are found to be 0.1 mA/㎠ and 0.51 %, respectively, at a potential of 0.72 V vs. RHE. Our results illustrate that the ZnO nanostructured thin film has promising potential as an efficient photoanode for PEC water splitting.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.114-118
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• 2011

Dye-Sensitized Solar Cells(DSSCs) consist of a titanium dioxide($TiO_2$) nano film of the photo electrode, dye molecules on the surface of the $TiO_2$ film, an electrolyte layer and a counter electrode. But two transparent conductive oxide(TCO) substrates are estimated to be about 60[%] of the total cost of the DSSCs. Currently novel TCO-less structures have been investigated in order to reduce the cost. In this study, we suggested a TCO-less DSSCs which has titanium double layer electrodes. Titanium double layer electrodes are formed by electron-beam evaporation method. Analytical instruments such as electrochemical impedance spectroscopy, scanning electron microscope were used to evaluate the TCO-less DSSCs. As a result, the proposed structure decreases energy conversion efficiency and short-circuit current density compared with the conventional DSSCs structure with FTO glass, while internal series impedance of TCO-less DSSCs using titanium double layer electrodes decreases by 27[%]. Consequently, the fill factor is improved by 28[%] more than that of the conventional structure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.457-460
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• 2006

Y doped zinc oxide (YZO) thin films were deposited on F doped $SnO_2$ (FTO) glass substrate by sol-gel method using the spin-coating system. A homogeneous and stable solution was prepared by dissolving acetate in the solution added diethanolamine as sol-gel stabilizer. YZO films were obtained after preheated on the hot-plate for 5minute before each coating; the number of coating was 3 times. After the coating of last step, annealing of YZO films performed at $450^{\circ}C$ for 30 minute. In order to confirming of a ultraviolet ray interruption and down-conversion effects, optical properties of YZO films, transmission spectrum and fluorescent spectrum were used. Also, for understanding the obtained results by experiment, the elestronic state of YZO was calculated using the density functional theory The results obtained by experiment were compared with calculated structure. The detail of electronic structure was obtained by the discrete variational Xa (DV-Xa) method, which is a sort of molecular orbital full potential method. The density of state and energy levels of dopant element were shown and discussed in association with optical properties.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.239-245
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• 2020

Synthesizing one-dimensional nanostructures of oxide semiconductors is a promising approach to fabricate highefficiency photoelectrodes for hydrogen production from photoelectrochemical (PEC) water splitting. In this work, vertically aligned zinc oxide (ZnO) nanorod arrays are successfully synthesized on fluorine-doped-tin-oxide (FTO) coated glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Zn metal thin film. The structural, optical and PEC properties of the ZnO nanorod arrays synthesized at varying levels of Zn sputtering power are examined to reveal that the optimum ZnO nanorod array can be obtained at a sputtering power of 20 W. The photocurrent density and the optimal photocurrent conversion efficiency obtained for the optimum ZnO nanorod array photoanode are 0.13 mA/㎠ and 0.49 %, respectively, at a potential of 0.85 V vs. RHE. These results provide a promising avenue to fabricating earth-abundant ZnO-based photoanodes for PEC water oxidation using facile hydrothermal synthesis.