Browsing by Author "Hsieh, Ming-Yang"

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A look into the origin of shunt leakage current of Cu(In,Ga)Se-2 solar cells via experimental and simulation methods
(2013-10-01)
Liao, Yu-Kuang
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Kuo, Shou-Yi
;
Hsieh, Ming-Yang
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Lai, Fang-I
;
Kao, Ming-Hsuan
This study investigates how to apply space-charge-limited (SCL) current to describe shunt leakage current in a CIGS solar cell. Possible factors inducing SCL current have been observed through conductive atomic force microscopy (C-AFM), which supports the SCL current theory, describing the shunt current of a CIGS solar cell. In simulations derived from experimental data, deviation of dark IV curves is due to flaws in the real device. These flaws are absent in simulation, but investigation verifies the characteristics of SCL current component's experimental IV curves within shunt leakage current. A device with a metal/CIGS/metal structure could simulate SCL current and confirm its characteristics. Such a simulated structure, representing flaws inserted into a CIGS solar cell, generates the same dark-current behavior revealed in experimental dark IV curves. This study investigates the response of dark current to varying sizes of the flaw within the CIGS solar cell. (C) 2013 Elsevier B.V. All rights reserved.
Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition
(2017-04-01)
Liao, Yu-Kuang
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Liu, Yung-Tsung
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Hsieh, Dan-Hua
;
Shen, Tien-Lin
;
Hsieh, Ming-Yang
Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin filmswith the thickness of a fewnanometers on rough surfaces. We present a new "paradigm shift" non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In, Ga) Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase.
Dandelion-shaped nanostructures for enhancing omnidirectional photovoltaic performance
(2013)
Kuo, Shou-Yi
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Hsieh, Ming-Yang
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Han, Hau-Vei
;
Lai, Fang-I
;
Tsai, Yu-Lin
Broadband and omnidirectional light harvesting is important in photovoltaic technology because of its wide spectral range of radiation and the sun's movement. This study reports the fabrication and characterization of zinc oxide (ZnO) dandelions on Cu(In,Ga)Se-2 (CIGS) solar cells. The fabrication of dandelions involves the combination of self-assembled polystyrene (PS) nanospheres and the hydrothermal method, which is one of the simplest and cheapest methods of fabricating a three-dimensional, closely packed periodic structure. This study also investigates the optimization on dimension of the PS nanospheres using the rigorous coupled-wave analysis (RCWA) method. This study uses an angle-resolved reflectance spectroscope and a homemade rotatable photo I-V measurement to investigate the omnidirectional and broadband antireflections of the proposed dandelion structure. Under a simulated one-sun condition and a light incident angle of up to 60 degrees, cells with ZnO dandelions arrays enhanced the short-circuit current density by 31.87%. Consequently, ZnO dandelions are suitable for creating an omnidirectionally antireflective coating for photovoltaic devices.
Device Modeling of the Performance of Cu(In,Ga)Se-2 Solar Cells with V-Shaped Bandgap Profiles
(2014)
Kuo, Shou-Yi
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Hsieh, Ming-Yang
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Hsieh, Dan-Hua
;
Kuo, Hao-Chung
;
Chen, Chyong-Hua
The effect of Cu(In,Ga)Se-2 (CIGS) with V-shaped bandgap on device performance is investigated in detail. A series of Ga/(In+Ga) ratio are set to study the influence of V-shaped bandgap profile on the electricity of CIGS thin film solar cells. The modeling of device current density-voltage (J-V) curve and bandgap grading profile corresponded well to measurement results. Detailed characteristic and modeling results show that an increased gradient of bandgap from valley to the buffer layer CdS will result in a barrier and lead to an enhanced recombination in the valley. This phenomenon can be modified by the back electric field resulting from a gradient bandgap from valley (bandgap minimum) to the Mo back contact. These results indicate CIGS-based solar cells can achieve higher performance by optimizing the V-shaped bandgap profile.
Enhanced broadband and omnidirectional performance of Cu(In,Ga)Se-2 solar cells with ZnO functional nanotree arrays
(2013)
Hsieh, Ming-Yang
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Kuo, Shou-Yi
;
Han, Hau-Vei
;
Yang, Jui-Fu
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Liao, Yu-Kuang
An effective approach is demonstrated for enhancing photoelectric conversion of Cu(In,Ga)Se-2 (CIGS) solar cells with three-dimensional ZnO nanotree arrays. Under a simulated one-sun condition, cells with ZnO nanotree arrays enhance the short-circuit current density by 10.62%. The omnidirectional anti-reflection of CIGS solar cells with various ZnO nanostructures is also investigated. The solar-spectrum weighted reflectance is approximately less than 5% for incident angles of up to 60 degrees and for the wavelengths primarily from 400 nm to 1000 nm. This enhancement in light harvesting is attributable to the gradual refractive index profile between the ZnO nanostructures and air.
Flexible-textured polydimethylsiloxane antireflection structure for enhancing omnidirectional photovoltaic performance of Cu(In,Ga)Se-2 solar cells
(2014-02-10)
Kuo, Shou-Yi
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Hsieh, Ming-Yang
;
Han, Hau-Vei
;
Lai, Fang-I
;
Chuang, Tsung-Yeh
Because of the Sun's movement across the sky, broadband and omnidirectional light harvesting is a major development in photovoltaic technology. This study reports the fabrication and characterization of flexible-textured polydimethylsiloxane ( PDMS) film on Cu(In,Ga)Se-2 (CIGS) solar cells, which is one of the simplest and cheapest peel-off processes for fabricating a three-dimensional structure. A cell containing a textured PDMS film enhanced the short-circuit current density from 22.12 to 23.93 mA/cm(2) in a simulated one-sun scenario. The omnidirectional antireflection of CIGS solar cells containing various PDMS films is also investigated. This study uses an angle-resolved reflectance spectroscope to investigate the omnidirectional and broadband optical properties of the proposed PDMS film. This improvement in light harvesting is attributable to the scattering of the PDMS film and the gradual refractive index profile between the PDMS microstructures and air. The flexible-textured PDMS film is suitable for creating an antireflective coating for a diverse range of photovoltaic devices. (C) 2014 Optical Society of America
Modeling and Optimization of Sub-Wavelength Grating Nanostructures on Cu(In,Ga)Se-2 Solar Cell
(2012-10-01)
Kuo, Shou-Yi
;
Hsieh, Ming-Yang
;
Lai, Fang-I
;
Liao, Yu-Kuang
;
Kao, Ming-Hsuan
In this study, an optical simulation of Cu(In,Ga)Se-2 (CIGS) solar cells by the rigorous coupled-wave analysis (RCWA) method is carried out to investigate the effects of surface morphology on the light absorption and power conversion efficiencies. Various sub-wavelength grating (SWG) nanostructures of periodic ZnO:Al (AZO) on CIGS solar cells were discussed in detail. SWG nanostructures were used as efficient antireflection layers. From the simulation results, AZO structures with nipple arrays effectively suppress the Fresnel reflection compared with nanorod- and cone-shaped AZO structures. The optimized reflectance decreased from 8.44 to 3.02% and the efficiency increased from 14.92 to 16.11% accordingly. The remarkable enhancement in light harvesting is attributed to the gradient refractive index profile between the AZO nanostructures and air. (C) 2012 The Japan Society of Applied Physics
Realizing omnidirectional light harvesting by employing hierarchical architecture for dye sensitized solar cells
(2016)
Hsieh, Ming-Yang
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Lai, Fang-I
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Chen, Wei-Chun
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Hsieh, Min-Chi
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Hu, Hsiang-Yi
To improve the omnidirectional light-harvesting in dye-sensitized solar cells (DSSCs), here we present a dandelion-like structure composed of ZnO hemispherical shells and nanorods. Uniformly distributed hemispherical shells effectively suppress the reflection over the broadband region at incident angles up to 60 degrees, greatly improving the optical absorption of the DSSCs. In addition, modulating the length of the ZnO nanorods controls the omnidirectional characteristics of DSSCs. This phenomenon is attributed to the degree of periodicity of the ZnO dandelion-like structures. Cells with shorter rods exhibit a high degree of periodicity, thus the conversion efficiencies of the cells show specific angle-independent features. On the other hand, the cells with longer lengths reveal angle-dependent photovoltaic performance. Along with the simulation, the cells with dandelion-like ZnO structures can couple incident photons efficiently to achieve excellent broadband and omnidirectional light-harvesting performances experimentally, and the DSSCs enhanced the conversion efficiency by 48% at large incident angles. All these findings not only provide further insight into the light-trapping mechanism in these complex three-dimensional nanostructures but also offer efficient omnidirectional and broadband nanostructured photovoltaics for advanced applications.