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Pohang, South Korea

The recent surge of unveiled US patents on the intermediate reflectors for thin-film silicon (Si) photovoltaic (PV) devices reflects the paramount importance of light trapping to improve the conversion efficiency. Here, the recent patent issues on the intermediate reflectors of thin-film Si PV devices are reviewed. Highly transparent and conductive metal oxide intermediate reflectors have the advantage of the higher efficiency for the fabricated multi-junction solar cells compared to the Si alloy intermediate reflectors. However, their high lateral electrical conductivity leads to the lateral shunting during the monolithic series integration of segments. To avoid the lateral shunt creations, an additional laser scribe or a coating process that induces a high production cost is necessary. In addition, a low conversion efficiency for hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline Si (μc-Si:H) double-junction PV modules employing a metal oxide intermediate reflector stems from the decrease in the active area as a result of the additional process. Meanwhile, double-junction PV modules employing an n-type hydrogenated microcrystalline Si oxide (n-μc-SiO x:H) intermediate reflector provide a higher conversion efficiency. Since the Si alloy intermediate reflector can avoid the lateral shunting, it may be a promising option for cost-effective mass production of large-area thin-film Si multi-junction PV modules. Although the developed intermediate reflectors have the high potential, the current status is limited at the research and development (R&D) level. Therefore, the up-scaling with the low cost, high throughput, and high yield is a key technological mission for mass production. © 2014 Elsevier Ltd. Source

Myong S.Y.,Energy Randnter | Jeon L.S.,Energy Randnter
Current Applied Physics

We investigate the improvement of p-i-n type thin-film silicon (Si) solar cells by employing a hydrogenated n-type amorphous Si (n-a-Si:H)-based bilayer. The initial conversion efficiency (η) of a-Si:H single-junction solar cells is improved from 9.2 to 10.0%. The developed n-a-Si:H-based bilayer is also suitable for a-Si:H/hydgrogenated microcrystalline Si (μc-Si:H) double-junction solar cells, and thus initial η is improved from 10.4 to 10.8%. With a further optimization, initial η of 11.3% and stabilized η of 10.1% are achieved. Since the n-a-Si:H-based bilayer is easily formed using a conventional process, it can be a promising option for cost-effective mass production of large-area thin-film Si solar modules © 2013 Elsevier B.V. All rights reserved. Source

Yeop Myong S.,Energy Randnter | Won Jeon S.,Energy Randnter
Solar Energy Materials and Solar Cells

Color design for large-area hydrogenated amorphous silicon (a-Si:H) semi-transparent glass-to-glass (GTG) photovoltaic (PV) modules has been studied for the application to building integrated PV (BIPV) modules. Three-dimensional color space of CIE (Commission Internationale de l'éclairage) L∗a∗b∗(CIELAB) is adopted for a systematic color analysis. Three kinds of design configurations are invented by combining the transparency of back contacts and laser patterning techniques. In addition, the realization of emotionally stable and esthetic color is challenged using color back encapsulating materials. Transparent back contact (TBC)-type modules with green color are fabricated via the most simplified processes without sacrificing any active area. Bright and esthetic hybrid-type modules are also fabricated using additional laser-scribed patterns and blue encapsulating film. It is found that opaque back contact (OBC)-type module design is the best way to achieve target color together with the highest conversion efficiency. Because color of the back encapsulating materials does not deteriorate the conversion efficiency, the developed design concepts are promising options for large-area semi-transparent BIPV modules. © 2015 Elsevier B.V. All rights reserved. Source

Myong S.Y.,Energy Randnter | Jeon L.S.,Energy Randnter
Solar Energy Materials and Solar Cells

We have investigated light trapping of p-i-n type hydrogenated amorphous silicon (a-Si:H) single-junction and p-i-n-p-i-n type a-Si:H/hydrogenated microcrystalline silicon (μc-Si:H) double-junction solar cells by adopting the oxygen-content graded or the oxygen-content alternated hydrogenated n-type silicon oxide (SiOx:H) reflectors. The graded n-type SiO x:H back reflector effectively increases the optical path length of the p-i-n type a-Si:H single-junction solar cells due to the refractive index grading. Moreover, the alternated n-type SiOx:H back reflector comprising of highly hydrogen-diluted n-type a-Si:H (n-a-Si:H) sublayers having a high refractive index and highly hydrogen-diluted n-type a-SiOx:H sublayers having a low refractive index provides the further improvement for the optical path length of the p-i-n type a-Si:H single-junction solar cells due to the multiple reflection. Furthermore, the developed alternated n-type SiO x:H reflector is suitable for the back reflector as well as the intermediate reflector of the p-i-n-p-i-n type a-Si:H/μc-Si:H double-junction solar cells. As a result, the high initial efficiency (η) of 13.1% and stabilized η of 11.5% are achieved. The considerably thin (30-45 nm) alternated n-type SiOx:H reflectors can be easily prepared using the in situ plasma enhanced chemical vapor deposition (PECVD) technique. Since the alternated n-type SiOx:H reflector can avoid the lateral shunting problem during the monolithic series integration of segments, it is a promising option for cost effective mass production of large-area thin-film silicon solar modules. © 2013 Elsevier B.V. All rights reserved. Source

Myong S.Y.,Energy Randnter | Jeon S.W.,Energy Randnter
Solar Energy Materials and Solar Cells

We developed high throughput, high efficiency 1.43 m2 hydrogenated amorphous silicon (a-Si:H) single-junction photovoltaic (PV) modules using a two-step deposition for the intrinsic a-Si:H absorber with the high deposition rate of 0.41 nm/s. The developed module using the two-step deposition method leads to higher initial maximum power (Pmax) due to the reduced recombination loss at the p/i interface, compared to the a-Si:H single-junction PV module fabricated by the conventional one-step deposition with the low deposition rate of 0.20 nm/s. In addition, the developed module exhibits moderate light-induced degradation ratio of 26.1% in an outdoor exposure test with accumulated solar irradiance >380 kWh/m2. Thus, the comparable energy output gain is confirmed via a long-term outdoor field test. Consequently, superior throughput of the developed module over the conventional module is possible with comparable stabilized performance. © 2014 Elsevier B.V. Source

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