Photovoltaic Power Generation Technology Research Association PVTEC

Tsukuba, Japan

Photovoltaic Power Generation Technology Research Association PVTEC

Tsukuba, Japan
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Nunomura S.,Japan National Institute of Advanced Industrial Science and Technology | Katayama H.,Panasonic | Yoshida I.,Photovoltaic Power Generation Technology Research Association PVTEC
Plasma Sources Science and Technology | Year: 2017

Hydrogen (H) atom kinetics has been investigated in capacitively coupled very high frequency (VHF) discharges at powers of 16-780 mW cm-2 and H2 gas pressures of 0.1-2 Torr. The H atom density has been measured using vacuum ultra violet absorption spectroscopy (VUVAS) with a micro-discharge hollow cathode lamp as a VUV light source. The measurements have been performed in two different electrode configurations of discharges: conventional parallel-plate diode and triode with an intermediate mesh electrode. We find that in the triode configuration, the H atom density is strongly reduced across the mesh electrode. The H atom density varies from ∼1012 cm-3 to ∼1010 cm-3 by crossing the mesh with 0.2 mm in thickness and 36% in aperture ratio. The fluid model simulations for VHF discharge plasmas have been performed to study the H atom generation, diffusion and recombination kinetics. The simulations suggest that H atoms are generated in the bulk plasma, by the electron impact dissociation (e + H2 e + 2H) and the ion-molecule reaction (H2 + + H2 + H). The diffusion of H atoms is strongly limited by a mesh electrode, and thus the mesh geometry influences the spatial distribution of the H atoms. The loss of H atoms is dominated by the surface recombination. © 2017 IOP Publishing Ltd.


Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Matsui T.,Japan National Institute of Advanced Industrial Science and Technology | Koida T.,Japan National Institute of Advanced Industrial Science and Technology | Matsubara K.,Japan National Institute of Advanced Industrial Science and Technology | And 5 more authors.
Applied Physics Letters | Year: 2015

We report a high-efficiency triple-junction thin-film silicon solar cell fabricated with the so-called substrate configuration. It was verified whether the design criteria for developing single-junction microcrystalline silicon (μc-Si:H) solar cells are applicable to multijunction solar cells. Furthermore, a notably high short-circuit current density of 32.9 mA/cm2 was achieved in a single-junction μc-Si:H cell fabricated on a periodically textured substrate with a high-mobility front transparent contacting layer. These technologies were also combined into a-Si:H/μc-Si:H/μc-Si:H triple-junction cells, and a world record stabilized efficiency of 13.6% was achieved. © 2015 AIP Publishing LLC.


Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Matsui T.,Japan National Institute of Advanced Industrial Science and Technology | Saito K.,Fukushima University | Kondo M.,Japan National Institute of Advanced Industrial Science and Technology | Yoshida I.,Photovoltaic Power Generation Technology Research Association PVTEC
Progress in Photovoltaics: Research and Applications | Year: 2015

Dielectric films with anti-reflective sub-wavelength structures are applied to thin-film silicon solar cells to improve the light incoupling at the front surface. It is shown that the sub-wavelength structure must be combined with a proper light-trapping texture to enhance the absorption within the solar cells. The effectiveness of dielectric films with sub-wavelength structures is demonstrated by an increase of the short-circuit current density of a microcrystalline silicon cell from 29.1 to 30.4 mA/cm2Dielectric films with anti-reflective sub-wavelength structures are applied to thin-film silicon solar cells to improve the light incoupling at the front surface. It is verified that modification of the refractive index of the incident medium using dielectric films with sub-wavelength structures is beneficial to reduce the average reflectivity of Si solar cells with an anti-reflective coating based on optical interference. It is also shown that the sub-wavelength structure must be combined with a proper light-trapping texture to enhance the absorption within thin-film silicon solar cells. The effectiveness of dielectric films with sub-wavelength structures is demonstrated by an increase of the short-circuit current density of a microcrystalline silicon cell from 29.1 to 30.4 mA/cm2 in a designated area of 1 cm2. The optical interplay between the dielectric films and the light-trapping textures is also discussed. © 2015 John Wiley Sons, Ltd.


Matsui T.,Japan National Institute of Advanced Industrial Science and Technology | Bidiville A.,Japan National Institute of Advanced Industrial Science and Technology | Maejima K.,Photovoltaic Power Generation Technology Research Association PVTEC | Sai H.,Japan National Institute of Advanced Industrial Science and Technology | And 9 more authors.
Applied Physics Letters | Year: 2015

Hydrogenated amorphous silicon (a-Si:H) films, used for light absorbers of p-i-n solar cells, were deposited at various deposition rates (Rd) ranging over two orders of magnitude (Rd ∼ 2 × 10-3-3 × 10-1 nm/s) by using diode and triode plasma-enhanced chemical vapor deposition (PECVD). The impact of varying Rd on the light-soaking stability of the solar cells has been investigated. Although a reduction of Rd mitigates the light-induced degradation in the typical range of Rd (>10-1 nm/s), it remains present even in the very low Rd (<10-2 nm/s), indicating that the metastable effect persists in a-Si:H regardless of Rd. The best performing cell, whose a-Si:H absorber is characterized by low amount of metastable defect and high bandgap, can be obtained at Rd of ∼1-3 × 10-2 nm/s by triode PECVD. By applying such a-Si:H in the improved p-i-n devices, we demonstrate two record independently confirmed stabilized efficiencies of 10.22% for single-junction and 12.69% for a-Si:H/hydrogenated microcrystalline silicon (μc-Si:H) tandem solar cells. © 2015 AIP Publishing LLC.


Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Saito K.,Photovoltaic Power Generation Technology Research Association PVTEC | Hozuki N.,Photovoltaic Power Generation Technology Research Association PVTEC | Kondo M.,Japan National Institute of Advanced Industrial Science and Technology
Applied Physics Letters | Year: 2013

Periodically textured back reflectors with hexagonal dimple arrays are applied to thin-film microcrystalline silicon (μc-Si:H) solar cells. When the textures have a moderate aspect ratio, the optimum period for obtaining a high short circuit current density (JSC) is found to be equal to or slightly larger than the cell thickness. If the cell thickness exceeds the texture period, the cell surface tends to be flattened and texture-induced defects are generated, which constrain the improvement in JSC. Based on these findings, we have fabricated optimized μc-Si:H cells achieving a high efficiency exceeding 10% and a JSC of 30 mA/cm2. © 2013 American Institute of Physics.


Matsui T.,Japan National Institute of Advanced Industrial Science and Technology | Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Saito K.,Photovoltaic Power Generation Technology Research Association PVTEC | Kondo M.,Japan National Institute of Advanced Industrial Science and Technology
Japanese Journal of Applied Physics | Year: 2012

We have applied a triode electrode configuration in the plasma-enhanced chemical vapor deposition (PECVD) process to grow intrinsic hydrogenated amorphous silicon (a-Si:H) light absorbers for the fabrication of p-i-n junction solar cells. Although the deposition rate is lower (0.1- 0.3 Å/s) than that of the conventional diode PECVD process, the light-soaking stability of the solar cell is markedly improved and less sensitive to the cell thickness due to the reduced Si-H 2 bond density in the a-Si:H i-layer. The a-Si:H single-junction solar cells exhibit low light-induced degradation of conversion efficiency (Δι/ι ini ∼ 10%) in comparison with that of high-efficiency solar cells reported to date. By applying the improved a-Si:H layers as top-cell absorbers in a-Si:H/hydrogenated microcrystalline silicon (μc-Si:H) tandem device, the light-induced degradation can be reduced even further (Δι/ι ini ≲ 5%). As a result, we obtain confirmed stabilized efficiencies of 9.6 and 11.3% for a-Si:H single-junction and a-Si:H/μc-Si:H tandem solar cells, respectively. © 2012 The Japan Society of Applied Physics.


Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Saito K.,Photovoltaic Power Generation Technology Research Association PVTEC | Kondo M.,Japan National Institute of Advanced Industrial Science and Technology
Applied Physics Letters | Year: 2012

Periodically textured back reflectors with hexagonal dimple arrays are applied to thin-film microcrystalline silicon (μc-Si:H) solar cells for enhancing their photon absorption and photovoltaic performance. In a systematic survey of 1 -μm-thick μc-Si:H cells, the best performance is obtained with a period of 1.5 μm and an aspect ratio of 0.20-0.25 with a high current density exceeding 26 mA/cm 2 and a marked efficiency of 10.1. These results demonstrate the high potential of periodic textures or surface gratings for improving the conversion efficiency of thin-film silicon solar cells. © 2012 American Institute of Physics.


Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Koida T.,Japan National Institute of Advanced Industrial Science and Technology | Matsui T.,Japan National Institute of Advanced Industrial Science and Technology | Yoshida I.,Photovoltaic Power Generation Technology Research Association PVTEC | And 2 more authors.
Applied Physics Express | Year: 2013

We developed advanced light management techniques and applied them to single-junction microcrystalline silicon solar cells to improve their current density and conversion efficiency. A high short-circuit current density of 30.8 mA/cm2 is attained in a 3-μm-thick cell aided by the superior light-trapping effect of periodically textured back reflectors, and by the reduced absorption loss from the high-mobility transparent conductive oxide films. In addition, an unprecedented efficiency of 10.5% is independently confirmed in a 1.8-μm-thick cell with the same structure. These results indicate the importance of light management for further efficiency improvements in thin-film silicon solar cells. © 2013 The Japan Society of Applied Physics.


Matsui T.,Japan National Institute of Advanced Industrial Science and Technology | Sai H.,Japan National Institute of Advanced Industrial Science and Technology | Saito K.,Photovoltaic Power Generation Technology Research Association PVTEC | Kondo M.,Japan National Institute of Advanced Industrial Science and Technology
Progress in Photovoltaics: Research and Applications | Year: 2013

Hydrogenated amorphous silicon (a-Si: H) films are prepared by plasma-enhanced chemical vapor deposition (PECVD) with a triode electrode configuration in which a SiH4-H2 glow-discharge plasma is confined spatially away from the substrate. Although the deposition rate (0.1-0.5 Å/s) is lower than that of the conventional diode PECVD process (2.5 Å/s), the light-induced degradation in conversion efficiency (Δη/ηini) of a single-junction solar cell is substantially reduced (e.g., Δη/ηini ~ 10% at an absorber thickness of ti = 250 nm), and efficiencies after light soaking (LS) maintain >9% for ti = 180-390 nm. By applying the improved a-Si: H layers as top cell absorbers in a-Si: H/hydrogenated microcrystalline silicon (μc-Si: H) tandem solar cells, the light-induced degradation can be reduced further (e.g., Δη/ηini ~ 5% at ti = 250 nm). As a result, we obtain confirmed stabilized efficiencies of 9.6% (LS condition: 100 mW/cm2, 50 °C, 1000 h) and 11.9% (LS condition: 125 mW/cm2, 48°C, 310 h) for a-Si: H single-junction and a-Si: H/μc-Si: H tandem solar cells, respectively. Copyright © 2012 John Wiley & Sons, Ltd.


Saito K.,Photovoltaic Power Generation Technology Research Association PVTEC | Kondo M.,Japan National Institute of Advanced Industrial Science and Technology
Journal of Non-Crystalline Solids | Year: 2012

We have proposed the mechanism of the <110> directional growth of microcrystalline silicon (μc-Si) thin films deposited by PECVD (plasma enhanced chemical vapor deposition) from SiH 4 and H 2 gas mixture, where dimeric radicals act a key role to form bridge nuclei for the ledge formation on the (110) facet. In order to look further into details of the mechanism, we investigated other important factors that influence the growth of μc-Si in <110> direction in terms of their impact on crystallinity with varying deposition temperature. The enhancement of surface diffusion length of radicals is inferred from the enlargement of the crystalline grain size accompanied with the increase of the deposition temperature. The growth in <110> direction is also promoted as the deposition temperature increases. Therefore, it is suggested that the surface diffusion length of radicals is another key factor that governs the crystalline growth in <110> direction. The growth mechanism of μc-Si thin films in <110> direction is discussed in terms of the relation between the surface diffusion length of monomeric radicals depending on the substrate surface temperature and the average space of bridges depending on the density of dimeric radicals on the growing surface. © 2012 Elsevier B.V. All rights reserved.

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