• Transactions on Electrical and Electronic Materials
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• v.16 no.4
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• pp.206-211
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• 2015

We investigated the formation of a nanopyramidal structure and fabricated nanotextured Si solar cells using an Ag metal-assisted chemical etching process. The nanopyramidal structure was formed on a Si flat surface and the nanotexturing process was performed on the p-type microtextured Si surface. The nanostructural formation shows a transition from nanopits and nanopores to nanowires with etching time. The nanotextured surfaces also showed the photoluminescence spectra with an enhanced intensity in the wavelength range of 1,100~1,250 nm. The photoreflectance of the nanotextured Si solar cells was strongly reduced in the wavelength range of 337~596 nm. However, the quantum efficiency is decreased in the nanotextured samples due to the increased nanosurface recombination. The nanotexturing process provides a better p-n junction impedance of the nanotextured cells, resulting in an enhanced shunt resistance and fill factor which in turn renders the possibility of the increased conversion efficiency.

• Current Photovoltaic Research
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• v.3 no.1
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• pp.10-15
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• 2015

Cu doping by copper or $Cu_2Te$ materials enhances p+ formation in CdTe near the back contact interface, allowing better formation of ohmic contact. However, the Cu in CdTe junction is also considered as a principal component of CdTe cell degradation. In this paper, Na-doped ZnTe layer was employed as a back contact material to improve the stability of CdTe solar cells. As a process variable, post $CdCl_2$ treatment of CdS/CdTe film was conducted before or after depositing ZnTe:Na on CdTe. The change of the photovoltaic properties of CdTe cells were investigated with aging time. Low-temperature photoluminescence analysis was conducted to describe the degradation mechanism. The result showed that the CdTe solar cells with better stability compare to Cu contact were achieved using an optimized ZnTe:Na back contact.

• Current Photovoltaic Research
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• v.6 no.2
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• pp.39-42
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• 2018

When the PV module is illuminated in a high temperature region, solar cells are also exposed to the high temperature external environment. The operating temperature of the solar cell inside the module is increased, which causes the power drops. Various efforts have been made to reduce the operating temperature and compensate the power of solar cells according to the outdoor temperature such as installing of a cooling system. Researches have been also reported to lower the operating temperature of solar cells by improving the heat dissipation properties of the backsheet. In this study, we conducted a test to measure the internal temperature of each module components and the external temperature when the light was irradiated according to the surrounding temperature. Backsheets with different thermal conductivities were compared in the test. Finally, in order to explain the temperature difference between the solar cell and the outside of the module, we proposed an evaluation method of the heat transfer characteristics of photovoltaic modules with different backsheet.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.438-438
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• 2009

We have investigated the effect of forming gas annealing for Upgraded Metallurgical Grade (UMG)-silicon solar cell in order to obtain low-cost high-efficiency cell using post deposition anneal at a relatively low temperature. We have observed that high concentration hydrogenation effectively passivated the defects and improved the minority carrier lifetime, series resistance and conversion efficiency. It can be attributed to significantly improved hydrogen-passivation in high concentration hydrogen process. This improvement can be explained by the enhanced passivation of silicon solar cell with antireflection layer due to hydrogen re-incorporation. The results of this experiment represent a promising guideline for improving the high-efficiency solar cells by introducing an easy and low cost process of post hydrogenation in optimized condition.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.412-415
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• 2008

In a research on the practical dye-sensitized solar cell, a study on a large module have preference because module must be able to generate the proper current that is possible to convert electrically. So the parallel connection of dye-sensitized solar cells which outputs a large current easily is essential. However, there is a current loss in a paralle connection of dye-sensitized solar cells and the loss becomes larger according to increasing the number of parallel connection. In this study, we analyzed the cause of the current loss in the parallel connection by using the equivalent circuit analysis. One DSC used in this experiment had an active area $8cm^2$(4.62cm$\times$1.73cm) and it attained a conversion efficiency of 5.43% under 1 sun illumination ($P_{in}$ of 100 mW/$cm^2$) using a solar simulator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.153-158
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• 2012

We use UV(ultraviolet)-$O_3$ treatment to increase the surface area and porosity of $TiO_2$ films in dye-sensitized solar cells (DSSCs). After the UV-$O_3$ treatment, surface area and porosity of the $TiO_2$ films were increased, the increased porosity lead to amount of dye loading and solar conversion efficiency was improved. Field emission scanning electron microscopy images clearly showed that the nanocrystalline porosity of films were increased by UV-$O_3$ treatment. The Brunauer, Emmett, and Teller surface area of the $TiO_2$ films were increased from $0.71cm^2/g$ to $1.31cm^2/g$ by using UV-$O_3$ treatment for 20 min. Also, UV-$O_3$ treatment of $TiO_2$ films significantly enhanced their solar conversion efficiency. The efficiency of the films without treatment was 4.9%, and was increased to 5.6% by UV-$O_3$ treatment for 20 min. Therefore the process enhanced the solar conversion efficiency of DSSCs, and can be used to develop high sensitivity DSSCs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.7
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• pp.616-621
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• 2009

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating(ARC) and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si ARC layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layers were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The structure of porous Si layers was investigated with SEM. The formation of a nanoporous Si layer about 100nm thick on the textured silicon wafer result in a reflectance lower than 5% in the wavelength region from 500 to 900nm. Such a surface modification allows improving the Si solar cell characteristics. An efficiency of 13.4% is achieved on a monocrystalline silicon solar cell using the electrochemical technique.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.295-298
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• 2007

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating(ARC) and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si ARC layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layers were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The structure of porous Si layers was investigated with SEM. The formation of a nanoporous Si layer about 100nm thick on the textured silicon wafer result in a reflectance lower than 5% in the wavelength region from 500 to 900nm. Such a surface modification allows improving the Si solar cell characteristics. An efficiency of 13.4% is achieved on a monocrystalline silicon solar cell using the electrochemical technique.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.109-109
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• 2006

Screen printing (SP) metal contact is typically applied to the solar cells for mass production. However, SP metal contact has low aspect ratio, low accuracy, hard control of the substrate penetration and unclean process. On the other hand, photo lithograpy (PL) metal contact can reduce defects by metal contact. In this investigation, PL metal contact was obtained the multi-layer structure of Ti/Pd/Ag by e-beam process. We applied SP metal contact and PL metal contact to single crystalline silicon solar cells, and demonstrated the difference of conversion efficiency. Because PL metal contact silicon solar cell has Jsc (short circuit current density) better than silicon solar cell applied SP metal contact.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.239.1-239.1
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• 2011

Dye sensitized solar cells (DSC) are promising devices for inexpensive, nontoxic, transparent, and large-scale solar energy conversion. Generally thick $TiO_2$ nanoporous films act as efficient photoanodes with their large surface area for absorbing light. However, electron transport through nanoparticle networks causes the slowdown and the loss of electron transport because of a number of interparticle boundaries inside the conduction path. We have studied DSCs with precisely dimension-controlled $TiO_2$ nanotubes array as photoanode. $TiO_2$ nanotubes array is prepared by template-directed fabrication method with atomic layer deposition. Well-ordered nanotubes array provides not only large surface area for light absorbing but also direct pathway for electrons with minimalized grain boundaries. Large enlongated anatase grains in the nanotubes could enhance the conductivity of electrons, but also suppress the recombination with holes through defect sites during diffusion into the electrode. To study the effect of grain boundaries, we fabricated two kinds of nanotubes which have different grain sizes by controlling deposition conditions. And we studied electron conduction through two kinds of nanotubes with different grain structures. The solar cell performance was studied as a function of thickness and grain structures. And overall solar-to-electric energy conversion efficiencies of up to 7% were obtained.