[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Conductometric semiconducting metal oxide gas sensors have been widely used and investigated in the detection of gases. Investigations have indicated that the gas sensing process is strongly related to surface reactions, so one of the important parameters of gas sensors, the sensitivity of the metal oxide based materials, will change with the factors influencing the surface reactions, such as chemical components, surface-modification and microstructures of sensing layers, temperature and humidity. In this brief review, attention will be focused on changes of sensitivity of conductometric semiconducting metal oxide gas sensors due to the five factors mentioned above.

Metal oxide gas sensors: Sensitivity and influencing factors

Transparent conductors as solar energy materials: A panoramic review

Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion Besides, doping is also an effective method to decrease particle size and improve gas sensing properties Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given

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Metal Oxide Nanostructures and Their Gas Sensing Properties: A Review

Aligned Single‐Crystalline Si Nanowire Arrays for Photovoltaic Applications

Silicon-based tandem solar cells with efficient use of the solar spectrum are desirable for a next generation-commercial photovoltaic system. It has been widely investigated elsewhere using perovskites or III-V cells as top cell materials for high efficiency and stability. However, perovskite and III-V top cells are still unsuitable for mass production as well as expansion and integration with silicon solar cell production processes so far. Two-terminal bifacial Si/Si tandem cell by bonding with transparent conductive adhesive (TCA) is reported here. The current matching can maximize the efficiency by controlling the opening area of the top cell, which makes the bottom cell also able to absorb sunlight in the short wavelength region that is absorbed by the top cell as well, without being limited to the thickness or bandgap of the top cell. The Si/Si tandem solar cell achieved short circuit current density of 25.195 mA/cm2 after current matching by 36% opening ratio of top cell.

Highly Efficient Bifacial Silicon/Silicon Tandem Solar Cells

Transparent conductive oxides have an important role of thin-film solar cell to the side of cost and performance.
Especially, an Al doped ZnO film is a very promising material for thin-film solar cell fabrication because of the easy
synthesis method as well as the cheap cost induced on the wide availability of its constituent raw materials. The Al-doped
ZnO films were prepared by metal organic chemical vapor deposition using a diethylzinc, water vapor and
trimethylaluminum (TMA). The introduction of TMA doping source has a great influence on the electrical resistivity and
diffused light to wide wavelength range. The haze factor of Al doped ZnO achieved 43 % at 600 nm without additional
surface texturing process by simple TMA doping. In this study, the choice of AZO TCO allows the achievement of
energy conversion efficiencies to 7.7 %.

Self textured transparent conductive oxide film for efficiency improvement in solar cell

Various fluoride films on a glass substrate were prepared and characterized to provide a seed layer for silicon (Si) film growth. The XRD analysis on CaF/sub 2//glass illustrated [220] preferential orientation and showed lattice mismatch less than 0.69% with Si. This paper demonstrates microcrystalline silicon (/spl mu/c-Si) film growth at a low substrate temperature of 300/spl deg/C by using a CaF/sub 2//glass substrate. The /spl mu/c-Si films exhibited crystallization in [111] and [220] planes, grain size of 700 /spl Aring/, crystalline volume fraction over 65%, dark- and photo-conductivity ratio of 124, activation energy of 0.49 eV, and dark conductivity less than 4/spl times/10/sup -7/ S/cm.

Microcrystalline silicon films using a fluoride seed layer on glass substrates for solar cell applications


 The screen-printing process for making good contact of electrodes with the top layer of solar cells is crucial for enhancing the electrical properties of a solar cell. This paper reports the experimental approach adopted for the process of electrode formation and the resulting shape of electrodes in silicon-based heterojunction (SHJ) solar cells. It was observed that good contact between electrodes and the top transparent conductive oxide (TCO) layer strongly depends on the squeegee pressure, curing temperature, and curing time. By optimizing the squeegee pressure at 0.350 MPa, snap-off distance of 1.4 mm, squeegee speed of 80 mm/sec, curing temperature of 180°C, and curing time of 30 minutes, the height to width ratio (aspect ratio) of the fabricated electrodes was achieved at ~0.66. The results have been verified through 3D laser profiler, field emission scanning electron microscopy, transfer length method, and light current-voltage measurements. The SHJ solar cells were fabricated using an optimized condition and successfully achieved splendid properties of short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and efficiency (η) up to 40.57 mA/cm2, 723 mV, 81.03%, and 23.79%, respectively.

Optimization of the Electrode Formation Mechanism for Crystalline Silicon Heterojunction Solar Cells

Proposed is a method for manufacturing a selective emitter using a surface structure, the method includes: preparing a wafer; forming fine first surface unevenness in each of front and rear faces of the wafer; forming a texturing-inhibiting film on each of the front and rear faces of the wafer; partially patterning the front texturing-inhibiting film to expose a portion of the front face of the wafer; forming second surface unevenness in the exposed portion of the wafer, wherein the second surface unevenness has a roughness greater and deeper than a roughness of the first surface unevenness; removing the texturing-inhibiting films; and forming a selective emitter on a surface of the wafer having the first surface unevenness and the second surface unevenness defined therein using a doping process.

Junsin Yi

Papers

Highly Efficient Bifacial Silicon/Silicon Tandem Solar Cells

Self textured transparent conductive oxide film for efficiency improvement in solar cell

Microcrystalline silicon films using a fluoride seed layer on glass substrates for solar cell applications

Optimization of the Electrode Formation Mechanism for Crystalline Silicon Heterojunction Solar Cells

Method for manufacturing selective emitter using surface structure and solar cell including selective emitter using surface structure