• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.378-378
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• 2011

본 연구에서는 ZnO 나노선 기판을 제작하여 그 위에 밴드갭이 낮은 물질인 CdS, CdSe를 증착시킨 후 p-type 반도체 물질인 CuSCN을 증착시켜 안정성이 향상된 양자점 감응형 태양전지를 제작하였다. ZnO 나노선 기판은 투명한 FTO 기판 위에 ZnO를 진공증착시켜 seed layer를 제작하고 그 위에 $10{\mu}m$정도의 길이의 나노와이어를 성장시킨 후, 밴드갭이 낮은 CdS, CdSe 물질과의 다중접합을 이용하여 제작하고, 이러한 나노선 구조위에 chemical solution deposition을 이용하여 ${\beta}$-CuSCN을 형성시켰다. 양자점 감응형 태양전지는 ZnO 나노선을 photoanode로 이용하고 ZnO 나노선은 암모니아수와 아연염을 이용한, 비교적 저온의 수열합성법을 통해 합성하였고, sensitizer로 쓰인 CdS, CdSe 물질은 CBD방식을 통하여 합성된 나노선 위에 in-situ로 접합시켰다. 또한, 기존의 액체전해질을 이용한 양자점 감응형 태양전지의 안정성을 향상시키기 위해 p-type의 반도체 물질인 CuSCN물질을 propyl sulfide를 이용, ${\sim}80^{\circ}C$의 열을 가하여 in-situ 방식으로 다공성 구조에 효율적으로 접합이 가능하도록 deposition하였다. 일반적으로, CuSCN film은 홀 전도체로서의 장점을 지닌 반면, 전도성이 낮은 단점이 있기 때문에 이를 향상시키기 위해서 첨가제를 이용, 농도에 따라서 전도도가 향상되고 셀의 성능이 향상되는 것을 확인하였다. 이와 같이 합성된 구조는 주사전자현미경(SEM), X-선 회절(XRD), 솔라시뮬레이터 등의 분석장비를 이용하여 태양전지로서의 특성을 분석하였다. 또한 안정성 평가를 위하여 시간에 따른 셀의 특성변화도 비교하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.676-676
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• 2013

무기물 양자점을 광감응 염료로 사용하는 경우 양자점의 사이즈 조절만으로 밴드갭을 조절할 수 있어 광학적 특성 조절이 용이하며, 유기 염료보다 광흡수 능력이 뛰어난 장점을 가진다. 특히 카드뮴 계열의 CdS, CdSe 양자점을 순차적으로 증착하여 사용하는 경우 가시광 전 영역을 효율적으로 흡수, 이용할 수 있어 광전기화학 셀의 광전극으로 사용 시 높은 성능을 기대할 수 있다. 하지만, 카드뮴 계열 양자점의 경우 광전기화학 셀로의 구동에 있어 안정성이 낮은 문제점이 있으며, 이는 양자점에 남아있는 정공이 관여하는 양자점 부식 반응으로 인한 것이다. 본 연구에서는 보다 안정적이면서도 고효율의 광전기화학적 수소생산 시스템을 위해, CdSe/CdS 양자점 감응형 ZnO 나노선 광전극에 IrO2 촉매물질을 증착하였다. CdSe/CdS 양자점이 가시광 전 영역을 흡수하며, ZnO 나노선 구조를 통해 생성된 광전자를 효율적으로 포집하여 높은 광전류 특성을 기대할 수 있다. 나아가 산소생산용 조촉매로 많이 사용하는 $IrO_2$ 촉매 물질의 추가증착을 통해 양자점에서 생긴 정공을 빼 줌으로서 정공이 관여하는 양자점 부식 반응을 방지할 수 있다. 실험결과 촉매물질의 증착 이후 광전류 생성 특성 및 수소생산량이 증가하였으며, 안정성 또한 상당히 향상된 것을 확인할 수 있었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.432.2-432.2
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• 2014

Recently, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED)[1]. In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[2] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QD LED, two kinds of hybrid organic materials, [poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo)(F8BT) + poly(N,N'-bis (4-butylphenyl)-N,N'-bis(phenyl)benzidine (poly-TPD)] and [4,4'-N,N'-dicarbazole-biphenyl (CBP) + poly-TPD], were adopted as hole transport layer having high highest occupied molecular orbital (HOMO) level for improving hole transport ability. At a low-operating voltage of 8 V, the device emits orange and red spectral radiation with high brightness up to 2450 and 1420 cd/m2, and luminance efficacy of 1.4 cd/A and 0.89 cd/A, respectively, at 7 V applied bias. Also, the carrier transport mechanisms for the QD LEDs are described by using several models to fit the experimental I-V data.

• Toxicological Research
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• v.29 no.1
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• pp.35-42
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• 2013

Quantum dots (QDs) have received considerable attention due to their potential role in photosensitization during photodynamic therapy. Although QDS are attractive nanomaterials due to their novel and unique physicochemical properties, concerns about their toxicity remain. We suggest a combination strategy, CdSe/ZnS QDs together with curcumin, a natural yellow pigment from turmeric, to reduce QD-induced cytotoxicity. The aim of this study was to explore a potentially effective cancer treatment: co-exposure of HL-60 cells and human normal lymphocytes to CdSe/ZnS QDs and curcumin. Cell viability, apoptosis, reactive oxygen species (ROS) generation, and DNA damage induced by QDs and/or curcumin with or without ultraviolet A (UVA) irradiation were evaluated in both HL-60 cells and normal lymphocytes. In HL-60 cells, cell death, apoptosis, ROS generation, and single/double DNA strand breaks induced by QDs were enhanced by treatment with curcumin and UVA irradiation. The protective effects of curcumin on cell viability, apoptosis, and ROS generation were observed in normal lymphocytes, but not leukemia cells. These results demonstrated that treatment with QD combined with curcumin increased cell death in HL-60 cells, which was mediated by ROS generation. However, curcumin acted as an antioxidant in cultured human normal lymphocytes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.40-40
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• 2010

CdSe nanocrystals (NCs) have been decorated on singlewalled carbon nanotubes (SWCNTs) by combining a method of chemically modified substrate along with gate-bias control. CdSe/ZnS core/shell quantum dots were negatively charged by adding mercaptoacetic acid (MAA). The silicon oxide substrate was decorated by octadecyltrichlorosilane (OTS) and converted to hydrophobic surface. The negatively charged CdSe NCs were adsorbed on the SWCNT surface by applying the negative gate bias. The selective adsorption of CdSe quantum dots on SWCNTs was confirmed by confocal laser scanning microscope. The measured photocurrent clearly demonstrates that CdSe NCs decorated SWCNT can be used for photodetector and solar cell that are operable over a wide range of wavelengths.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.246.1-246.1
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• 2014

Over the past several years, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED). In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[1] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QDLEDs, blend of poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo) and poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] are used as hole transporting layer (HTL) to improve hole transporting property. At the operating voltage of 8 V, the QDLED device emitted spectrally orange color lights with high luminance up to 2450 cd/m2, and showed current efficacy of 0.6 cd/A, respectively.

• The Korean Journal of Applied Statistics
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• v.26 no.4
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• pp.569-579
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• 2013

In the field of single-molecule spectroscopy, it is essential to analyze luminescence Intensity changes that result from a single molecule. With the CdSe/ZnS core-shell structured quantum dot photon emission data Bayesian multiple change-point estimation is done with the gamma prior for Poisson parameters and truncated Poisson distribution for the number of change-points.

• Progress in Medical Physics
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• v.28 no.4
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• pp.226-231
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• 2017

The aim is to investigate the spectra responsibilities of QD (Quantum Dot) for the innovation of new dosimetry application for therapeutic Megavoltage X-ray range. The unique electrical and optical properties of QD are expected to make it a good sensing material for dosimeter. This study shows the spectra responsibility of toluene based ZnCd QD and PPO (2.5-diphenyloxazol) mixed liquid scintillator. The QDs of 4 sizes corresponding to an emission wavelength (ZnCdSe/ZnS:$440{\pm}5nm$, ZnCdSeS:470, 500, $570{\pm}5nm$) were utilized. A liquid scintillator for control sample was made of toluene, PPO. The Composition of QD loaded scintillators are about 99 wt% Toluene as solvent, 1 wt% of PPO as primary scintillator and 0.05, 0.1, 0.2 and 0.4 wt% of QDs as solute. For the spectra responsibility of QD scintillation, they were irradiated for 30 second with 6 MV beam from a LINAC ($Infinity^{TM}$, Elekta). With the guidance of 1.0 mm core diameter optical fiber, scintillation spectrums were measured by a compact CCD spectrometer which could measure 200~1,000 nm wavelength range (CCS200, Thorlabs). We measured the spectra responsibilities of QD loaded organic liquid scintillators in two scintillation mechanisms. First was the direct transfer and second was using wave shifter. The emission peaks from the direct transfer were measured to be much smaller luminescent intensity than based on the wavelength shift from the PPO to QDs. The emission peak was shifted from PPO emission wavelength 380 nm to each emission wavelength of loaded QD. In both mechanisms, 500 nm QD loaded samples were observed to radiate in the highest luminescence intensity. We observed the spectra responsibility of QD doped toluene based liquid scintillator in order to innovate QD dosimetry applicator. The liquid scintillator loading 0.2 wt% of 500 nm emission wavelength QD has most superior responsibility at 6 MV photon beam. In this study we observed the spectra responsibilities for therapeutic X-ray range. It would be the first step of innovating new radiation dosimetric methods for radiation treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.97-97
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• 2010

We demonstrate the hybrid polymer-quantum dot based multi-functional device (Organic bistable devices, Light-emitting diode, and Photovoltaic cell) with a single active-layer structure consisting of CdSe/ZnS semiconductor quantum-dots (QDs) dispersed in a poly N-vinylcarbazole (PVK) and 1,3,5-tirs- (N-phenylbenzimidazol-2-yl) benzene (TPBi) fabricated on indium-tin-oxide (ITO)/glass substrate by using a simple spin coating technique. The multi-functionality of the device as Organic bistable device (OBD), Light Emitting Diode (LED), and Photovoltaic cell can be successfully achieved by adding an electron transport layer (ETL) TPBi to OBD for attaining the functions of LED and Photovoltaic cell in which the lowest unoccupied molecular orbital (LUMO) level of TPBi is positioned at the energy level between the conduction band of CdSe/ZnS and LiF/Al electrode (band-gap engineering). Through transmission electron microscopy (TEM) study, the active layer of the device has a p-i-n structure of a consolidated core-shell structure in which semiconductor QDs are uniformly and isotropically adsorbed on the surface of a p-type polymer core and the n-type small molecular organic materials surround the semiconductor QDs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.393-398
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• 2019

A poly[bis(4-butypheny)-bis(phenyl)benzidine] (poly-TPD) and poly(9-vinylcarbazole) (PVK) bilayer was employed as a hole transport layer (HTL) in solution-processed CdSe/ZnS quantum dot light-emitting diodes (QLEDs). The thickness of the PVK layer spin-coated onto the poly-TPD layer, whose thickness was fixed to 40 nm, was varied, with PVK layer thicknesses of 0 nm, 35 nm, 45 nm, and 55 nm. Because the thickness of the PVK can determine the hole transport properties of the HTL, a PVK thickness that maximizes the performance of the HTL for the QLEDs was investigated. By employing the optimized PVK thickness of 45 nm, the current efficiency of the QLED exhibited a 1.74 times improvement when compared with that of the QLED with poly-TPD based HTL without PVK. This was mainly attributed to the decrease in the energy barrier between the HTL and the quantum dot (QD) emitting layer (EML).