Browsing by Author "Liang, Shin-Wei"

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Applications of mu c-SiOx:H as integrated n-layer and back transparent conductive oxide for a-Si:H/mu c-Si:H tandem cells
(2014-05-01)
Liang, Shin-Wei
;
Huang, Yen-Tang
;
Hsu, Hung-Jung
;
Hsu, Cheng-Hang
;
Tsai, Chuang-Chuang
We have prepared n-type hydrogenated microcrystalline silicon oxide [mu c-SiOx:H(n)] films with oxygen contents from 0 to 37.3 at. % by varying the CO2-to-SiH4 flow ratio in a plasma-enhanced chemical vapor deposition (PECVD) system. By using mu c-SiOx:H(n) as an effective replacement for integrated mu c-Si:H(n) and indium-tin oxide (ITO), mu c-Si:H single-junction and a-Si:H/mu c-Si:H tandem cells exhibited significantly improved efficiencies of 6.35 and 10.53%, respectively. The improvement of the single-junction and tandem cells mainly arose from the enhancement of long-wavelength optical absorption in mu c-Si:H absorbers, which was confirmed by a quantum efficiency instrument showing a markedly enhanced spectral response at wavelengths from 600 to 1100 nm. Moreover, all the PECVD processes, except the metal contact, had an advantage of in situ deposition without breaking vacuum, thereby minimizing contamination of the interface. The simplified cell fabrication can enhance the fill factor, which will benefit industrial production. (C) 2014 The Japan Society of Applied Physics
Development of Hydrogenated Microcrystalline Silicon-Germanium Alloys for Improving Long-Wavelength Absorption in Si-Based Thin-Film Solar Cells
(2014)
Huang, Yen-Tang
;
Hsu, Hung-Jung
;
Liang, Shin-Wei
;
Hsu, Cheng-Hang
;
Tsai, Chuang-Chuang
Hydrogenated microcrystalline silicon-germanium (mu c-Si1-xGex:H) alloys were developed for application in Si-based thin-film solar cells. The effects of the germane concentration (R-GeH4) and the hydrogen ratio (R-H2) on the mu c-Si1-xGex:H alloys and the corresponding single-junction thin-film solar cells were studied. The behaviors of Ge incorporation in a-Si1-xGex:H and mu c-Si1-xGex:H were also compared. Similar to a-Si1-xGex:H, the preferential Ge incorporation was observed in mu c-Si1-xGex:H. Moreover, a higher R-H2 significantly promoted Ge incorporation for a-Si1-xGex: H, while the Ge content was not affected by R-H2 in mu c-Si1-xGex:H growth. Furthermore, to eliminate the crystallization effect, the 0.9 mu m thick absorbers with a similar crystalline volume fraction were applied. With the increasing R-GeH4, the accompanied increase in Ge content of mu c-Si1-xGex:H narrowed the bandgap and markedly enhanced the long-wavelength absorption. However, the bias-dependent EQE measurement revealed that too much Ge incorporation in absorber deteriorated carrier collection and cell performance. With the optimization of R-H2 and R-GeH4, the single-junction mu c-Si1-xGex:H cell achieved an efficiency of 5.48%, corresponding to the crystalline volume fraction of 50.5% and Ge content of 13.2 at.%. Compared to mu c-Si:H cell, the external quantum efficiency at 800nm had a relative increase by 33.1%.
Development of plasma-enhanced chemical vapor deposition microcrystalline silicon oxide as a replacement for N-type or back transparent conducting oxide layers in amorphous silicon single-junction solar cells
(2014-07-01)
Liang, Shin-Wei
;
Hsu, Hung-Jung
;
Hsu, Cheng-Hang
;
Tsai, Chuang-Chuang
;
光電工程學系
The n-type hydrogenated microcrystalline silicon oxide (mu c-SiOx:H(n)) thin films with varied electrical and optical properties were prepared. We employed mu c-SiOx:H(n) as a replacement for n-type hydrogenated amorphous silicon (a-Si: H(n)) or back transparent conducting oxide (TCO) layers in hydrogenated amorphous silicon (a-Si:H) single-junction solar cells. Compared to the standard cell with a-Si:H(n)/ITO/Ag back reflecting structure, the cell using a-Si: H(n)/mu c-SiOx:H(n)/Ag or mu c-SiOx:H(n)/Ag showed a similar or even better performance. This improvement of cell performance mainly arose from the increased short-circuit current density (J(SC)) that originated from the increased long wavelength (580-660 nm) absorption in the absorber confirmed by the quantum efficiency measurement. The "all plasma-enhanced chemical vapor deposition" (if the front TCO and metal contact are disregarded) process without TCO (indium tin oxide, ITO) sputtering can simplify the fabrication and result in better interface quality. Compared to the standard cell, the conversion efficiency of a-Si:H cells using an 80 nm thick mu c-SiOx:H(n)/Ag back reflecting structure was enhanced from 9.32% to 9.84%, with V-OC = 0.90 V, J(SC) = 14.84 mA/cm(2), and FF = 73.7%.
Effect of TCO/mu c-Si:H Interface Modification on Hydrogenated Microcrystalline Silicon Thin-Film Solar Cells
(2013)
Liang, Shin-Wei
;
Hsu, Cheng-Hang
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Tsai, Chuang-Chuang
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光電工程學系
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Department of Photonics
The effects of H-2 plasma exposure on optical, electrical, and structural properties of fluorine-doped tin oxide (FTO) and AZO/FTO substrates have been investigated. With increasing the time of H-2-plasma exposure, the hydrogen radical and ions penetrated through the FTO surface to form more suboxides such as SnO and metallic Sn, which was confirmed by the XPS analysis. The Sn reduction on the FTO surface can be effectively eliminated by capping the FTO with a very thin layer of sputtered aluminum-doped zinc oxide (AZO), as confirmed by the XPS analysis. By using the AZO/FTO as front TCO with the subsequent annealing, the p-i-n mu c-Si:H cell exhibited a significantly enhanced JSC from 15.97 to 19.40 mA/cm(2) and an increased conversion efficiency from 5.69% to 7.09%. This significant enhancement was ascribed to the effective elimination of the Sn reduction on the FTO surface by the thin AZO layer during the Si-based thin-film deposition with hydrogen-rich plasma exposure. Moreover, the subsequent annealing of the sputtered AZO could lead to less defects as well as a better interface of AZO/FTO.
Improved light management in a-Si:H/a-Si1-xGex:H tandem cells by employing multi-functional n-type microcrystalline silicon oxide
(2014-05-01)
Hsu, Hung-Jung
;
Liang, Shin-Wei
;
Huang, Yen-Tang
;
Hsu, Cheng-Hang
;
Tsai, Chuang-Chuang
In this work, the development of plasma-enhanced chemical vapor deposition (PECVD) mu c-SiOx:H(n) and its application to a-Si:H/a-Si1-xGex:H tandem cells as the intermediate reflecting layer (IRL) and back reflector (BR) is presented. The n-type microcrystalline silicon oxide [mu c-SiOx:H(n)] was used as multifunctional layers in silicon thin-film solar cells owing to its wide bandgap and low refractive index. In the development of mu c-SiOx:H(n), increasing RF power increased film oxygen content, which widened the bandgap while reducing dark conductivity. Applying the mu c-SiOx:H to a-Si:H/a-Si1-xGex:H tandem cells as IRL and BR significantly improved cell performance. The mu c-SiOx:H(n) IRL increases the current of the top cell, thus improving the light management in a-Si:H/a-Si1-xGex:H tandem cells. On the other hand, the mu c-SiOx:H(n) can be used as the BR replacing the n-type a-Si:H and ITO layers. The mu c-SiOx:H increased cell conversion efficiency by 12.9% as IRL, and by 9.7% as BR, achieving 10.03% efficiency. (C) 2014 The Japan Society of Applied Physics
Optimization of a-Si1-xGex:H single-junction and a-Si:H/a-Si1-xGex:H tandem solar cells with enhanced optical management
(2014-07-01)
Hsu, Hung-Jung
;
Liang, Shin-Wei
;
Hsu, Cheng-Hang
;
Tsai, Chuang-Chuang
;
光電工程學系
This work aimed at improving the optical management of a-Si: H/a-Si1-xGex:H tandem cells and a-Si1-xGex:H single-junction cells. To improve the optical management, the effects of the a-Si1-xGex:H bandgap, the bandgap graded absorber and the n-type mu c-SiOx:H back reflecting layer on the cell performance were investigated. Optical reflection spectra, internal quantum efficiency, external quantum efficiency (EQE), and cell performance were used to evaluate the improvement of the optical properties of solar cells. The tandem cells with a-Si1-xGex:H bandgap of 1.53 eV exhibited sufficient optical absorption from 630 to 900 nm and thus lead to higher J(SC). Second, the EQE of a-Si1-xGex:H single-junction cell was significantly enhanced from 630 to 720 nm by employing bandgap graded absorber that relatively improved the J(SC) by 3.8% despite that the reduction in EQE from 720 to 900 nm compared to the cell without bandgap grading. Moreover, the mu c-SiOx:H(n)/Ag back reflector showed higher optical reflection than a-Si:H(n)/Ag did, which relatively improved the J(SC) by 12.3%. The cell with mu c-SiOx:H(n)/Ag back reflector exhibited a comparable J(SC) and efficiency to the cell with ITO-Ag. The previously mentioned approaches are relevant to enhance the optical management in cells and can be applied to silicon-based thin-film solar cells.