• Current Photovoltaic Research
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• v.1 no.2
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• pp.115-121
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• 2013

ZnO film has been used for CIGS solar cells as a buffer layer as itself or by doping Mg and Sn; ZnO film also has been used as a transparent conducting layer by doping Al or B for solar cells. Since ZnO itself is a host material for many applications it is necessary to understand the electrical and optical properties of ZnO film itself with various preparation conditions. We prepared ZnO films by converting ZnS precursor into ZnO film by thermal annealing. ZnO film was formed at low temperature as low as $500^{\circ}C$ by annealing a ZnS precursor layer in air. In the air annealing, the electrical resistivity decreased monotonically with increasing annealing temperature; the intensity of the green photoluminescence at 505 nm increased up to $750^{\circ}C$ annealing. The electrical resistivity further decreased and the intensity of green emission also increased in reducing atmospheres. The results suggest that deep-level defects originated by oxygen vacancy enhanced green emission, which reduce light transmittance and enhance the recombination of electrons in conduction band and holes in valence. More oxidizing environment is necessary to obtain defect-free ZnO film for higher transparency.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.245-252
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• 2009

Changes in the surface morphology and light scattering of textured Al doped ZnO thin films on glass substrates prepared by rf magnetron sputtering were investigated. As-deposited ZnO:Al films show a high transmittance of above 80% in the visible range and a low electrical resistivity of $4.5{\times}10^{-4}{\Omega}{\cdot}cm$. The surface morphology of textured ZnO:Al films are closely dependent on the deposition parameters of heater temperature, working pressure, and etching time in the etching process. The optimized surface morphology with a crater shape is obtained at a heater temperature of $350^{\circ}C$, working pressure of 0.5 mtorr, and etching time of 45 seconds. The optical properties of light transmittance, haze, and angular distribution function (ADF) are significantly affected by the resulting surface morphologies of textured films. The film surfaces, having uniformly size-distributed craters, represent good light scattering properties of high haze and ADF values. Compared with commercial Asahi U ($SnO_2$:F) substrates, the suitability of textured ZnO:Al films as front electrode material for amorphous silicon thin film solar cells is also estimated with respect to electrical and optical properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.458-458
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• 2013

We investigated a study on the thermal degradation of boron doped zinc-oxide (BZO) layer which used as a transparent conducting layer on the Cu (In1-xGax) Se2 (CIGS) based thin film solar cells. Devices were annealed under the temperature of $100^{\circ}C$ or 100 hours and then Hall measurement was carried out to characterize the parameters of mobility (${\mu}Hall$), resistivity (${\rho}$), conductivity (${\sigma}$) and sheet resistance (Rsh). The initial values of ${\mu}Hall$, ${\rho}$, ${\sigma}$ and Rsh were $29.3cm^2$/$V{\cdot}s$, $2.1{\times}10^{-3}{\Omega}{\cdot}cm$, $476.4{\Omega}^{-1}{\cdot}cm^{-1}$ and $19.1{\Omega}$/${\Box}$ respectively. After the annealing process, the values were $4.5cm^2$/$V{\cdot}s$, $12.8{\times}10^{-3}{\Omega}{\cdot}cm$, $77.9{\Omega}^{-1}{\cdot}cm^{-1}$ and $116.6{\Omega}$/${\Box}$ respectively. We observed that ${\mu}Hall$ and ${\sigma}$ were decreased, and ${\rho}$ and Rsh were increased. In this study, BZO layer plays an important role of conducting path for electrons generated by incident light onthe CIGS absorption layer. Therefore, the degradation of BZO layer characterized by the parameters of ${\mu}Hall$, ${\rho}$, ${\sigma}$ and Rsh, affect to the cell efficiency.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.6
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• pp.571-575
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• 2005

In order to improve the efficiency of dye-sensitized solar cell (DSSC), $TiO_2$ electrode screen-printed on transparent conducting oxide (TCO) substrate was sintered in variation with different temperature$(350\;to\;550^{\circ}C)$. $TiO_2$ electrode on fluorine doped tin oxide (FTO) glass was assembled with Pt counter electrode on FTO glass. I-V properties of DSSCs were measured under solar simulator. Also, effect of sintering temperature on surface morphology of $TiO_2$ films was investigated to understand correlation between its surface morphology and sintering temperature. Such surface morphology was observed by atomic force microscopy (AFM). Below sintering temperature of $500^{\circ}C$, efficiency of DSSCs was relatively lower due to lower open circuit voltage. Oppositely, above sintering temperature of $500^{\circ}C$, efficiency of DSSCs was relatively higher due to higher open circuit voltage. In both cases, lower fill factor (FF) was observed. However, at sintering temperature of $500^{\circ}C$, both efficiency and fill factor of DSSCs were mutually complementary, enhancing highest fill factor and efficiency. Such results can be explained in comparison of surface morphology with schematic diagram of energy states on the $TiO_2$ electrode surface. Consequently, it was considered that optimum sintering temperature of a-terpinol included $TiO_2$ paste is at $500^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.1
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• pp.7-11
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• 2014

Recently, the buffer layers consisting of poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT-PSS) are extensively used to improve power conversion efficiency (PCE) of organic solar cells. However, PEDOT-PSS is not suitable for mass production of organic solar cells due to its intrinsic acid and hygroscopic properties. Moreover, because of chemical reactions between indium tin oxide (ITO) layer and PEDOT-PSS layer, the interface is not stable. For these reasons, alternative materials such as $V_2O_5$ have been developed to be an effective buffer layer. In this work, we used $V_2O_5$/Ag/ITO multilayer structure for the anode buffer layer. With variation of thickness of Ag layer, we investigated the optical and electrical properties of $V_2O_5$/Ag/ITO multi-layer films. As a result, we found that the electrical properties were improved with increasing Ag thickness while optical transmittance decreases in visible wavelength region. From the calculation of figure of merit (FOM) which is used to evaluate proper structure for transparent of optoelectronic, $V_2O_5$/Ag/ITO multilayer electrode was optimized with 4 nm thick Ag layer in optical (88% in transmittance) and electrical ($4{\times}10^{-4}{\Omega}cm$) properties. This indicates that $V_2O_5$/Ag/ITO multilayer electrode could be a candidate for the anode of optoelectronic devices.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.57.2-57.2
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• 2010

투명전도 산화막(Transparent conducing oxide: TCO)은 태양 전지, 터치패널, 가스 센서 등 여러 분야에 적용할 수 있는 물질로서 전기 전도성과 광 투과성을 동시에 가진다. 높은 전기 전도성과 광 투과성을 가지는 Sb:$In_2O_3$(ITO)는 투명전도 산화막 재료로써 가장 일반적으로 사용되고 있으나 인듐의 매장량 한계로 인해 가격이 높다는 단점이 있다. 본 연구에서는 ITO 대체 TCO 물질인 Al doped ZnO(AZO)를 rf magnetron sputter를 이용하여 최적의 수소 도핑량을 찾아 ITO의 전기적 광학적 성질과 비교하였다. AZO 박막은(ZnO:Al2O3 2wt.%)타겟을 이용하여 heater 온도 250도에서 슬라이드 글래스 및 코닝 글래스에 증착시켰고 비교군인 ITO박막은 (In2O3:$SnO_2$ 10wt.%)타겟을 이용하여 수소 도핑 없이 350도로 증착시켰다. AZO 및 ITO 박막의 전기적 특성은 hall measurement를 이용하여 측정하였고, UV-VIS spectrophotometer로 광학적 특성을 측정하였다. 수소 도핑량이 증가함에 따라 AZO 박막의 캐리어 농도가 증가하여 전기적 특성이 향상되었고, 가시광 영역에서 높은 평균 투과도를 유지 하였다. AZO 박막과 ITO 박막의 전기적 및 광학적 특성을 비교한 결과, 최적 수소 도핑량을 가진 AZO 박막은 ITO 박막에 준하는 특성을 보였다.

• Transactions of the KSME C: Technology and Education
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• v.1 no.1
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• pp.7-12
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• 2013

Tin oxide thin-films have been widely applied in various fields of high-technology industries due to their excellent physical and electric properties. Those applications are found in various sensors, heating elements of windshield windows, solar cells, flat panel displays as tranparent electrodes. In this study, we conducted an experiment for the deposition of $SnO_2$ on glass of 2nd Gen. size for the effective development of large-scale backplanes. As deposition temperatures or flow rates of the $SnCl_4$ as a precursor changed, the thickness of tin oxide thin-films, their sheet resistances, transmittances, and hazes varied considerably.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.168-168
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• 2010

Transparent conduction oxides (TCOs) films is extensively reported for optoelectronic devices application such as touch panels, solar cells, liquid crystal displays (LCDs), and organic light emitting diodes(OLEDs). Among the many TCO film, indium tin oxide(ITO) is in great demand due to the growth of flat panel display industry. However, indium is not only high cost but also its deposits dwindling. Therefore, many studies are being done on the transparent conductive oxides(TCOs). We fabricated a target of IZTO(In2O3:ZnO:SnO2=70:15:15 wt.%) reduced indium. Then, IZTO thin films were deposited on glass substrates by pulsed DC magnetron sputtering with various oxygen flow ratio. The substrate temperature was fixed at the room temperature. We investigated the electrical, optical, structural properties of IZTO thin films. The electrical properties of IZTO thin films were dependent on the oxygen partial pressure. As a result, the most excellent properties of IZTO thin films were obtained at the 3% of oxygen flow rate with the low resistivity of $7.236{\times}10^{-4}{\Omega}cm$. And also the optical properties of IZTO thin films were shown the good transmittance over 80%. These IZTO thin films were used to fabricated organic light emitting diodes(OLEDs) as anode and the device performances studied. The OLED with an IZTO anode deposited at optimized deposition condition showed good brightness properties. Therefore, IZTO has utility value of TCO electrode although it reduced indium and we expect it is possible for the IZTO to apply to flexible display due to the low processing temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.255-255
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• 2011

Zinc oxide based thin films have been extensively studied in recent several years because they have very interesting properties and zinc oxide is non-poisonous, abundant and cheap material. ZnO films are employed in different applications like transparent conductive layers in solar cells, protective coatings and so on. Wide industrial application of the ZnO films requires of development of cheap, effective and scalable technology. Typically used technologies don't completely satisfy the industrial requirements. In the present work, we studied effect of the deposition parameters on the structure and properties of ZnO films deposited by DC arc plasmatron. The varied parameters were gas flow rates, precursor composition, substrate temperature and post-deposition annealing temperature. Vapor of Zinc acetylacetone was used as source materials, oxygen was used as working gas and argon was used as the cathode protective gas and a transport gas for the vapor. The plasmatron power was varied in the range of 700-1500 watts. Flow rate of the gases and substrate temperature rate were varied in the wide range to optimize the properties of the deposited coatings. After deposition films were annealed in the hydrogen atmosphere in the wide range of temperatures. Structure of coatings was investigated using XRD and SEM. Chemical composition was analyzed using x-ray photoelectron spectroscopy. Sheet conductivity was measured by 4-point probe method. Optical properties of the transparent ZnO-based coatings were studied by the spectroscopy. It was shown that deposition by a DC Arc plasmatron can be used for low-cost production of zinc oxide films with good optical and electrical properties. Increasing of the oxygen content in the gas mixture during deposition allow to obtain high-resistive protective and insulation coatings with high adhesion to the metallic surface.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.447-454
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• 2014

Organic solar cells (OSCs) have intensively studied in recent years due to their advantages such as cost effectiveness and possibility of applications in flexible devices. In spite of the high power conversion efficiency (PCE) of 10 %, the OSCs still have a draw back of their low environmental stability due to the oxidization of aluminum cathode and etching of transparent conducting oxide as electrode. To solve these problems, the inverted structured OSCs (I-OSCs) having greatest potential for achieving an improvement of device performances are suggested. Therefore, there are a lot of studies to develope of interface layer based on organic/inorganic materials for the electron transport layer (ETL) and passivation layer, significant advancements in I-OSCs have driven the development of interface functional materials including electron transport layer. Recent efforts to employing 2D/3D zinc oxide (ZnO) based ETL into I-OSCs have produced OSCs with a power conversion efficiency level that matches the efficiency of ~9 %. In this review, the technical issues and recent progress of ZnO based ETL in I-OSCs to enhancement of device efficiency and stability in terms of materials, process and characterization have summarized.