Browsing by Author "Wang, Yi-Chih"

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Double-graded bandgap in Cu(In,Ga)Se-2 thin film solar cells by low toxicity selenization process
(2014-08-18)
Wang, Yi-Chih
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Shieh, Han-Ping D.
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交大名義發表
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光電工程學系
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顯示科技研究所
A low-toxic selenization with post gallium diffusion (PGD) treatment has been demonstrated to increase the bandgap in the surface Cu(In,Ga)Se-2 (CIGSe) absorbers and to form double-graded bandgap profiles to improve the cell efficiency. The CIGSe absorber with PGD for 5 min increased open-circuit voltage from 0.49 to 0.66V and efficiency from 9.2% to 13.2%, contributed by the enhancement of carrier recombination in the space-charge region. The reduction in short-circuit current from 30.8 to 29.9 mA/cm(2), attributed to the absorption loss in long-wavelength regions, can be potentially improved by further optimization of the minimum bandgap value in gradient valley. (C) 2014 AIP Publishing LLC.
Improvement of bandgap homogeneity in Cu(In,Ga)Se-2 thin films using a modified two-step selenization process
(2013-10-07)
Wang, Yi-Chih
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Shieh, Han-Ping D.
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光電工程學系
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顯示科技研究所
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Department of Photonics
A modified two-step selenization has been demonstrated to overcome inhomogeneous gallium distribution, an issue to lower energy bandgap in the space-charge region as well as cell efficiency. It was found that incorporating selenium into conventional precursors could accelerate the formation of CuInGaSe2 phase in the selenization to accordingly suppress the diffusion effect of gallium. By introducing a pre-heating treatment, this selenization enhanced the bandgap distribution with a back-surface field and an increase of bandgap in the space-charge region, consequently improving open circuit voltage (V-OC) by 25% and cell efficiency by 55%, respectively. (C) 2013 AIP Publishing LLC.
Photovoltaic electrical properties of aqueous grown ZnO antireflective nanostructure on Cu(In,Ga)Se-2 thin film solar cells
(2014-01-13)
Wang, Yi-Chih
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Lin, Bing-Yi
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Liu, Po-Tsun
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Shieh, Han-Ping D.
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光電學院
A solution-grown subwavelength antireflection coating has been investigated for enhancing the photovoltaic efficiency of thin film solar cells. The 100-nm-height ZnO nanorods coating benefited the photocurrent of Cu(In, Ga) Se-2 solar cells from 31.7 to 34.5 mA/cm(2) via the decrease of surface light reflectance from 14.5% to 7.0%, contributed by the gradual refractive index profile between air and AZO window layer. The further reduction of surface reflectance to 2.3% in the case of 540-nm-height nanorods, yet, lowered the photocurrent to 29.5 mA/cm(2), attributed to the decrease in transmittance. The absorption effect of hydrothermal grown ZnO nanorods was explored to optimize the antireflection function in enhancing photovoltaic performances. (C) 2013 Optical Society of America