• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.813-816
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• 2002

We investigate the junction between CdZnTe and a variety of metals with the aim of determining whether the choice of metal can improve the performance of X-ray image detectors, in particular minimizing the dark current. The samples consist of $5{\mu}m$ thick CdZnTe with top electrodes formed from In, Al, and Au. For each metal, current transients following application of valtages from -10V to 10V are measured for up to 1 hour. We find that dark currents depending on the metal used. The current is controlled by hole injection at the metal-CdZnTe junction and there is consistent trend with the metal's work function possibly and it seems that metal to CdZnTe layer junction is ohmic contact.

• Current Photovoltaic Research
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• v.5 no.1
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• pp.20-24
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• 2017

Recently, three-dimensional (3D) light harvesting structures are highly attracted because of their high light harvesting capacity and charge collection efficiencies. In this study, we have fabricated $Cu_2ZnSn(S_xSe_{1-x})_4$ based 3D thin film solar cells on PR patterned Molybdenum (Mo) substrates using photolithography technique. Specifically, Mo patterns were deposited on PR patterned Mo substrates by sputtering and the thin Cu-Zn-Sn stacked layer was deposited over this Mo patterns by sputtering technique. The stacked Zn-Sn-Cu precursor thin films were sulfo-selenized to form CZTSSe pattern. Finally, CZTSSe absorbers were coated with thin CdS layer using chemical bath deposition and ZnO window layer was deposited over CZTSSe/CdS using DC sputtering technique. Fabricated 3-D solar cells were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) analysis, Field-emission scanning electron microscopy (FE-SEM) to study their structural, compositional and morphological properties, respectively. The 3% efficiency is achieved for this kind of solar cell. Further efforts will be carried out to improve the performance of solar cell through various optimizations.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.4
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• pp.659-664
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• 2010

The ZnS/CdS thin films were made using 99.99% ZnS and CdS(Aldrich) powders in $7{\times}10^{-6}torr$. The ZnS layer was coated over the CdS layer on an AlOx membrane within a vacuum, at the average speed of $1{\AA}/sec$. After studying the ZnS/CdS and CdS thin films(both with the dimensions of 2.52nm), using fluorescence spectroscopy and comparing the respective results together, we found that although both of the resulting spectra peaked at 390nm, the ZnS/CdS thin films showed a narrower peak, and a higher intensity of photoluminescence than the CdS thin films. The particles of ZnS/CdS thin films also proved to be more homogeneous in size. In addition, the ZnS layer acted as a protective layer. Also, after studying the spectra of ZnS/CdS thin films taken 30 days after their preparation, we found no signs of aging. These results were verified through the scanning electron microscopy(SEM), EDX analysis, thin film X-ray diffraction, and luminescence spectroscopy.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2797-2801
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• 2023

CdZnTeSe (CZTS) has attracted attention for applications in X- and gamma-ray detectors owing to its improved properties compared to those of CdZnTe (CZT). In this study, we grew and processed single crystals of CZT and CZTS using the Bridgeman method to confirm the feasibility of using a dosimeter for high-energy X-rays in radiotherapy. We evaluated their linearity and precision using the coefficient of determination (R²) and relative standard deviation (RSD). CZTS showed sufficient RSD values lower than 1.5% of the standard for X-ray dosimetry, whereas CZT's RSD values increased dramatically under some conditions. CZTS exhibited an R² value of 0.9968 at 500 V/cm, whereas CZT has an R² value of 0.9373 under the same conditions. The X-ray response of CZTS maintains its pulse shape at various dose rates, and its properties are improved by adding selenium to the CdTe matrix to lower the defect density and sub-grain boundaries. Thus, we validated that CZTS shows a better response than CZT to high-energy X-rays used for radiotherapy. Further, the applicability of an onboard imager, a high-energy X-ray (>6 MV) image, is presented. The proposed methodology and results can guide future advances in X-ray dose detection.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.393-397
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• 2012

We report a new route to synthesize high quality zinc blende CdS and ZnS nanocrystals in noncoordinating solvent 1-octadecene, using dodecanethiol (DDT) molecules as both the sulfur source and surface capping ligands. Different reaction temperatures and Cd(Zn)/DDT molar ratios were tested to optimize the synthesis conditions. Absorption photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) pattern, and transmission electron microscopy (TEM) were used to characterize assynthesized nanocrystals. The narrow half width at the half-maximum on the long wavelength side of the firstexcitonic absorption peak and TEM images demonstrated nearly monodisperse size distributions of asprepared CdS, ZnS, and CdS/ZnS core/shell nanocrystals. Only trap emissions of the nanocrystals were detected when the amount of DDT was excessive, this came from the strong quenching effect of thiol groups on the nanocrystal surfaces. After overcoating with ZnS shells, band-gap emissions of CdS nanocrystals were partially recovered.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.309.1-309.1
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• 2013

현재까지 CIGS 박막 태양전지는 습식공정인 화학적 용액성장법을 사용하여 형성된 CdS버퍼층을 적용할 경우에 가장 높은 효율을 보이고 있다. 그러나, Cd의 독성 문제와 진공 공정과 호환되지 않는 습식공정 때문에 비독성 건식 공정 버퍼층에 대한 연구가 활발히 진행되고 있다. 습식 공정 CdS 버퍼층을 대체하기 위하여 CdS에 비해 밴드갭이 커서 단파장에서 광 손실이 적은 ZnS 버퍼층을 cracker 황화법을 이용하여 제작하여 CIGS 박막 태양전지에 적용하였다. ZnS 버퍼층을 성장시키기 위해 DC 스퍼터를 사용하여 Zn 박막을 증착한 후, cracker를 사용하여 황화반응을 시켰다. cracker의 cracking zone 온도에 따른 S 반응성을 ZnS 박막의 투과도 변화를 통하여 관찰하였다. 성장된 ZnS 박막은 X-ray diffraction와 Rutherford backscattering spectrometry을 이용하여 박막의 결정성과 조성을 분석하였고, SEM 측정을 통하여 박막의 단면 및 표면 형상을 관찰하였다. 그리고 reflection electron energy loss spectroscopy 분석을 통해 밴드갭을 측정하였다. $700^{\circ}C$의 cracking zone 온도, 3 nm의 Zn 두께, 1 분의 황화공정 조건에서 제작된 ZnS 박막을 CIGS 태양전지의 버퍼층으로 적용한 결과, 반사방지막 없이 12.6%의 변환효율을 얻었다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.1
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• pp.1-4
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• 2002

To obtain the blue emission of powder electroluminescent device, the emission properties of ZnS:Cu were estimated by the variation of applied frequency and the addition of dye to ZnS:Cu phosphor. The variation of applied frequency was from 400 to 4kHz and the addition ratio of dye was from 0 to 5 weight percent respectively. The increment of applied frequency made that emission peaks were shifted from 500.5nm and 460nm at 400Hz to 490nm and 450nm at 4kHz. CIE coordinate system was shifted from x=0.1647, y=0.3711 at 400Hz to x=0.1543, y=0.1856 at 4kHz. On the basis of applied voltage 100V, 400Hz, the increment of addition ratio of dye also made that emission peak was shifted from 505nm(0wt%) to 490nm(5wt%) and the CIE coordinate system was shifted from x=0.1647, y=0.3711(0wt%) to x=0.1334, y=0.2363 (5wt%). The brightness was increased from 60 cd/$m^2$(400Hz) to 174 cd/$m^2$(4kHz) with increment of frequency. When the addition ratio of dye was above 1wt%, the brightness was decreased below 42% of initial brightness and changed from 60 cd/$m^2$(0wt%) to 20.84 cd/$m^2$(5wt%).

• Korean Journal of Materials Research
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• v.32 no.11
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• pp.481-488
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• 2022

The Cu₂ZnSn(S_xSe_1-x)₄ (CZTSSe) absorbers are promising thin film solar cells (TFSCs) materials, to replace existing Cu(In,Ga)Se₂ (CIGS) and CdTe photovoltaic technology. However, the best reported efficiency for a CZTSSe device, of 13.6 %, is still too low for commercial use. Recently, partially replacing the Zn²⁺ element with a Cd²⁺element has attracting attention as one of the promising strategies for improving the photovoltaic characteristics of the CZTSSe TFSCs. Cd²⁺ elements are known to improve the grain size of the CZTSSe absorber thin films and improve optoelectronic properties by suppressing potential defects, causing short-circuit current (J_sc) loss. In this study, the structural, compositional, and morphological characteristics of CZTSSe and CZCTSSe thin films were investigated using X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), and Field-emission scanning electron microscopy (FE-SEM), respectively. The FE-SEM images revealed that the grain size improved with increasing Cd²⁺ alloying in the CZTSSe thin films. Moreover, there was a slight decrease in small grain distribution as well as voids near the CZTSSe/Mo interface after Cd²⁺ alloying. The solar cells prepared using the most promising CZTSSe absorber thin films with Cd²⁺ alloying (8 min. 30 sec.) exhibited a power conversion efficiency (PCE) of 9.33 %, J_sc of 34.0 mA/cm², and fill factor (FF) of 62.7 %, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.370-370
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• 2011

ZnO 나노 라드 위에 Quantum dot을 형성하고 최종적으로 TiO2를 Atomic Layer Deposition방법으로 증착하여, 그 passivation 효과가 solar cell의 효율에 미친 영향에 대한 실험을 진행하였다. 암모니아 솔루션을 이용한 Hydrothermal 방법으로 수직한 1차원 형태의 ZnO 나노라드를 TCO 기판 위에 성장시킨다. 여기에 잘 알려진 SILAR와 CBD 방법으로 CdS, CdSe 양자점을 증착한다. 그리고 amorphous TiO2로 표면을 덮는 과정을 거치는데, TiO2가 좁은 간격으로 형성된 ZnO라드 구조 위에서 균일하고 정밀하게 증착되도록 하기 위해 Atomic Layer Deposition을 이용하였다. 사용된 precursor는 Titanium isopropoxide와 H2O이며, 실험상에서 0~5 nm 두께의 TiO2 박막을 형성해 보았다. 다양한 분석 방법을 통해 TiO2/QDs/ZnO의 shell-shell-core 구조를 조사했다. (Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS)). 이를 solar cell에 적용하고 I-V curve를 통해 그 효율을 확인하였으며, Electrochemical Impedance Spectroscopy (EIS)를 통해서 재결합 측면에서 나타나는 변화 양상을 확인하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.625-630
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• 2017

ZnS was chemically deposited as a buffer layer alternative to CdS, for use as a Cd-free buffer layer in $Cu(In_{1-x}Ga_x)Se_2$ (CIGS) solar cells. The deposition of a thin film of ZnS was carried out by chemical bath deposition, following which the structural and optical properties of the ZnS layer were studied. For the experiments, zinc sulfate hepta-hydrate ($ZnSO_4{\cdot}7H_2O$), thiourea ($SC(NH_2)_2$), and ammonia ($NH_4OH$) were used as the reacting agents. The mole concentrations of $ZnSO_4$ and $SC(NH_2)_2$ were fixed at 0.03 M and 0.8 M, respectively, while that of ammonia, which acts as a complexing agent, was varied from 0.3 M to 3.5 M. By varying the mole concentration of ammonia, optimal values for parameters like optical transmission, deposition rate, and surface morphology were determined. For the fixed mole concentrations of $0.03M\;ZnSO_4{\cdot}7H_2O$ and $0.8M\;SC(NH_2)_2$, it was established that 3.0 M of ammonia could provide optimal values of the deposition rate (5.5 nm/min), average optical transmittance (81%), and energy band gap (3.81 eV), rendering the chemically deposited ZnS suitable for use as a Cd-free buffer layer in CIGS solar cells.