• Transactions of the Korean hydrogen and new energy society
• /
• v.33 no.1
• /
• pp.113-120
• /
• 2022

Quantum dots (QDs) are attractive photosensitizer candidates for application not only in solar cells but also in solar hydrogen generation. For the prepartion of highly efficient QD-sensitized photoelectrodes, it is important to reduce electron recombination at the photoanode/electrolyte interface. Here, we study on the coating condition of ZnS passivation layers on the photoanodes in QD-sensitized solar cells (QDSCs). The ZnS passivation layers are coated by successive ionic layer adsorption and reaction method, and as the cation precursor, zinc acetate and zinc nitrate are empolyed. Due to the higher pH of cation precursor solution, the ZnS loading is improved when the zinc acetate is used, compared to the zinc nitrate. This improved loading of ZnS leads to the reduced electron recombination at the surface of photoanodes and the enhaced conversion efficiency of QDSCs from 6.07% to 7.45%.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.370-370
• /
• 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 Telematics and Electronics A
• /
• v.32A no.9
• /
• pp.121-127
• /
• 1995

We have analyzed the double insulating layer consisting of anodic oxide and ZnS through TEM experiments. The use of double insulating layer for HgCdTe surface passivation is one of the promising passivation method which has been recently studied deeply and the double insulating layer is formed by the evaporation of ZnS on the top of anodic oxide layer grown in H$_{2}$O$_{2}$ electrolyte. The structure of anodic oxide layer on HgCdTe is amorphous but the structure of oxide layer after the evaporation of ZnS has been changed to micro-crystalline. The interface layer of 150.angs. thickness has been found between ZnS and anodic oxide layer and is estimated to be ZnO layer. The results of analysis on the chemical components of ZnS, the interface layer and anodic oxide layer have showed that Zn has diffused into the anodic oxide layer deeply while Hg has been significantly decreased from HgCdTe bulk to the top of oxide layer. The formation of ZnO interface layer and the change of structure of anodic oxide layer after the evaporation of ZnS are estimated to be defects or to induce the defects which might possibly affect the increase of the positive fixed charges shown in C-V measurements of HgCdTe MIS.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.380-380
• /
• 2011

ZnO 나노라드 위에 양자점을 증착한 후 그 위에 $TiO_2$를 ALD방법으로 증착하여 그 passivation 효과가 solar cell 효율에 미친 영향에 대한 실험을 진행하였다. Hydrothermal 방법으로 수직한 1차원 형태의 ZnO 나노라드를 성장시킨다. 여기에 SILAR 방법을 거쳐서 CdS 양자점을 증착시키고, 후에 CBD를 이용하여 CdSe 양자점을 증착시킨다. 여기에 마지막으로 amorphous $TiO_2$로 표면을 덮는 과정을 거치는데, $TiO_2$가 ZnO 라드 위에 균일하고 정밀하게 증착되도록 하기 위해서 Atomic Layer Deposition을 이용하였다. 다양한 분석 방법을 통해 $TiO_2$/CdSe/CdS/ZnO 구조를 조사하였으며, ZnO 나노라드 위에 $TiO_2$가 정교하게 올라간 것을 확인한 후에 solar cell에 적용하여 그 효율을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.267.1-267.1
• /
• 2016

본 연구에서는 nematic 액정의 종류 중 하나인 5CB (4-Cyano-4'-pentylbiphenyl) 물질을 박막 트랜지스터 (TFT)의 passivation 층으로 사용했을 때 그 전기적 특성향상을 확인하였다. RF-magnetron sputtering법으로 증착된 비정질 InGaZnO 박막을 활성층으로 사용한 TFT를 제작하여 그 활성층 위에 drop형식으로 passivation 하였다. 그 결과, drain current (I_DS)가 약 10배 정도 증가하고, linear region(V_D=0.5V)에서 mobility와 subthreshold slope(SS)이 각각 6.7에서 12.2, 0.3에서 0.2로 향상되는 것이 보였다. 이것은 gate bias가 인가되었을 때 freedericksz 전이를 통한 액정의 배향과 이때 형성된 dipole 형성에 의한 것으로 보이며, 이러한 LC의 배향은 편광현미경을 통하여 표면과 수직으로 배향한다는 사실을 확인 할 수 있었고 이 LC-passivation된 a-IGZO TFT의 전기적 특성의 향상에 대한 mechanism을 제시하였다. 그리고 배향한 LC가 가지는 dipole에 의해 bias stress 상황에서 독특한 electron trapping과 recovery의 증폭효과가 나타났다. V_G=+20V의 positive gate bias stress를 1000s동안 가했을 때, passivation되지 않은 a-IGZO TFT의 경우 +4V의 threshold voltage shift(${\Delta}V$_TH)가 발생되었고, 바로 -20V의 negative gate bias를 30s간 가해주었을 때 -2.5V의 ${\Delta}V$_TH가 발생하였다. 반면 LC-passivation된 a-IGZO TFT의 경우 각각 +5V와 -4V의 ${\Delta}V$_TH로 더 큰 변화를 가져왔다. 이러한 LC에 의한 electron trapping/recovery 증폭효과에 대한 model을 제시하였다.

• Journal of Powder Materials
• /
• v.24 no.6
• /
• pp.489-493
• /
• 2017

In this study, the surface passivation process for InP-based quantum dots (QDs) is investigated. Surface coating is performed with poly(methylmethacrylate) (PMMA) and thioglycolic acid. The quantum yield (QY) of a PMMA-coated sample slightly increases by approximately 1.3% relative to that of the as-synthesized InP/ZnS QDs. The QYs of the uncoated and PMMA-coated samples drastically decrease after 16 days because of the high defect state density of the InP-based QDs. PMMA does not have a significant effect on the defect passivation. Thioglycolic acid is investigated in this study for the effective surface passivation of InP-based QDs. Surface passivation with thioglycolic acid is more effective than that with the PMMA coating, and the QY increases from 1.7% to 11.3%. ZnS formed on the surface of the InP QDs and S in thioglycolic acid show strong bonding property. Additionally, the QY is further increased up to 21.0% by the photochemical reaction. Electron-hole pairs are formed by light irradiation and lead to strong bonding between the inorganic and thioglycolic acid sulfur. The surface of the InP core QDs, which does not emit light, is passivated by the irradiated light and emits green light after the photochemical reaction.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.54 no.11
• /
• pp.490-492
• /
• 2005

A study on radiation hardening of infrared(IR) detector, the chief component of IR camera was performed. The radiation test on IR sensor passivated with the ZnS by Co$^{60}$ gamma-ray over 1 Mrads showed the reduction in Ro by 1/100 which was related to the noise level. This effect that was caused by carrier trapping in the ZnS passivation layer increased the leakage current and resulted in degradation in the device performance. For the radiation hardening of IR devices we suggested the ones with CdTe passivation layer which had a tendency to reluctant to carrier trapping in its layer and developed test patterns. Radiation test to the patterns showed that the our CdTe passivated device could survived over 1 Mrad gamma-ray dose.

• Korean Journal of Materials Research
• /
• v.18 no.12
• /
• pp.640-644
• /
• 2008

ZnO/ZnS core/shell nanocrystals (${\sim}5-7\;nm$ in diameter) with a size close to the quantum confinement regime were successfully synthesized using polyol and thermolysis. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analyses reveal that they exist in a highly crystalline wurtzite structure. The ZnO/ZnS nanocrystals show significantly enhanced UV-light emission (${\sim}384\;nm$) due to effective surface passivation of the ZnO core, whereas the emission of green light (${\sim}550\;nm$) was almost negligible. They also showed slight photoluminescence (PL) red-shift, which is possibly due to further growth of the ZnO core and/or the extension of the electron wave function to the shell. The ZnO/ZnS core/shell nanocrystals demonstrate strong potential for use as low-cost UV-light emitting devices.

• Journal of Powder Materials
• /
• v.24 no.1
• /
• pp.1-5
• /
• 2017

We have investigated the washing method of as-synthesized CdSe/ZnS core/shell structure quantum dots (QDs) and the effective surface passivation method of the washed QDs using PMMA. The quantum yield (QY%) of as-synthesized QDs decreases with time, from 79.3% to 21.1%, owing to surface reaction with residual organics. The decreased QY% is restored to the QY% of as-synthesized QDs by washing. However, the QY% of washed QDs also decreases with time, owing to the absence of surface passivation layer. On the other hand, the PMMA-treated QDs maintained a relatively higher QY% after washing than that of the washed QDs that were kept in toluene solution for 30 days. Formation of the PMMA coating layer on CdSe/ZnS QD surface is confirmed by HR-TEM and FT-IR. It is found that the PMMA surface coating, when combined with washing, is useful to be applied in the storage of QDs, owing to its long-term stability.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 2000.06a
• /
• pp.35-58
• /
• 2000

The demand for sub-micrometer or nanometer functional ceramic powders with a better suspension behavior in aqueous media in increasing. Redispersible barium titanate (BT) nanocrystals, green light emitting Mn2+ doped Zn$_2$SiO$_4$ and ZnS nanoparticle phosphors were synthesized by a hydrothermal method or chemical precipitation with surface modification. The nanoparticle redispersibility for BT was achieved by using a polymeric surfactant. X-ray diffraction(XRD) results indicated that the BT particles are of cubic phase with 80 nm in size. XRD results of zinc silicate phosphor indicate that seeds play an important role in enhancing the nucleation and crystallization of Zn$_2$SiO$_4$ crystals in a hydrothermal condition. This paper describes and discuss the methods of surface modification, and the resulting related properties for BT, zinc silicate and zinc sulfide.