Browsing by Author "Kuo, Shou-Yi"

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A Comprehensive Study of One-Step Selenization Process for Cu(In1-xGax) Se-2 Thin Film Solar Cells
(2017-03-21)
Chen, Shih-Chen
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Wang, Sheng-Wen
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Kuo, Shou-Yi
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Juang, Jenh-Yih
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Lee, Po-Tsung
In this work, aiming at developing a rapid and environmental-friendly process for fabricating CuIn1-xGaxSe2 (CIGS) solar cells, we demonstrated the one-step selenization process by using selenium vapor as the atmospheric gas instead of the commonly used H2Se gas. The photoluminescence (PL) characteristics indicate that there exists an optimal location with superior crystalline quality in the CIGS thin films obtained by one-step selenization. The energy dispersive spectroscopy (EDS) reveals that the Ga lateral distribution in the one-step selenized CIGS thin film is intimately correlated to the blue-shifted PL spectra. The surface morphologies examined by scanning electron microscope (SEM) further suggested that voids and binary phase commonly existing in CIGS films could be successfully eliminated by the present one-step selenization process. The agglomeration phenomenon attributable to the formation of MoSe2 layer was also observed. Due to the significant microstructural improvement, the current-voltage (J-V) characteristics and external quantum efficiency (EQE) of the devices made of the present CIGS films have exhibited the remarkable carrier transportation characteristics and photon utilization at the optimal location, resulting in a high conversion efficiency of 11.28%. Correlations between the defect states and device performance of the one-step selenized CIGS thin film were convincingly delineated by femtosecond pump-probe spectroscopy.
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
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Hsieh, Ming-Yang
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Lai, Fang-I
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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.
Advanced Functional Nanomaterials Synthesis and Nanocrystal Growth Technology
(2015-01-01)
Chen, Wei-Chun
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Kuo, Hao-Chung
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Tiwari, Rajanish Nath
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Kuo, Shou-Yi
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Lai, Fang-I
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
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Shen, Tien-Lin
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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.
Characterization of large area Cu(In,Ga)Se-2 nanotip arrays via photoluminescence
(2012)
Liao, Yu-Kuang
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Lin, Woei-Tyng
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Hsieh, Dan-Hua
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Kuo, Shou-Yi
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Lai, Fang-I
In this study, photoluminescence (PL) measurements were used to characterized Cu(In,Ga)Se-2 nanotip arrays (CIGS NTRs). Large area CIGS NTRs were yielded by using one step Ar+ milling process without template. Formation mechanism of NTRs is due to a highly anisotropic milling effect of the quaternary components compound. In both CIGS thin films with and without NTRs, saturation effects of Donor-Acceptor Pair (DAP) had been observed while excitation power dependence PL measurements. Comparing with thin film CIGS without NTRs, it has revealed that the concentration DAP had been changed after formation of CIGS NTRs and had enhanced its carrier density of the p-type semiconductor.
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
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Lai, Fang-I
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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
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Kuo, Hao-Chung
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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.
Efficiency Improvement of Single-Junction In(0.5)Ga(0.5)P Solar Cell with Compositional Grading p-Emitter/Window Capping Configuration
(2010-01-01)
Chang, Yi-An
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Kuo, Hao-Chung
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Lu, Tien-Chang
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Lai, Fang-I
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Kuo, Shou-Yi
In this study a novel p-emitter/window capping configuration design applied to a p(+)-n In(0.5)Ga(0.5)P solar cell is developed. By grading the Ga and Al compositions in the interface between the p-In(0.5)Ga(0.5)P emitter and p-In(0.5)Al(0.5)P window layers, the output characteristics of the p(+)-n In(0.5)Ga(0.5)P solar cell are improved. It is found that the photoluminescence (PL) intensity is increased and the minority carrier lifetime obtained from room-temperature time-resolved (TR) PL measurement can be increased from 5.3 ns of the typical design to 7.0 ns, indicating that the application of compositional grading can improve crystal quality and the interface becomes smoother, thus reducing the nonradiative recombination losses. Both the short-circuit current and open-circuit voltage are increased correspondingly and the conversion efficiency is improved from 14.57% of the typical design to 15.32% of the new p-emitter/window configuration under one-sun air-mass 1.5 global illumination. (C) 2010 The Japan Society of Applied Physics
Efficiency Improvement of Single-Junction In0.5Ga0.5P Solar Cell with Compositional Grading p-Emitter/Window Capping Configuration
(2010-01-01)
Chang, Yi-An
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Kuo, Hao-Chung
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Lu, Tien-Chang
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Lai, Fang-I
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Kuo, Shou-Yi
In this study a novel p-emitter/window capping configuration design applied to a p(+)-n In0.5Ga0.5P solar cell is developed. By grading the Ga and Al compositions in the interface between the p-In0.5Ga0.5P emitter and p-In0.5Al0.5P window layers, the output characteristics of the p(+)-n In0.5Ga0.5P solar cell are improved. It is found that the photoluminescence (PL) intensity is increased and the minority carrier lifetime obtained from room-temperature time-resolved (TR) PL measurement can be increased from 5.3 ns of the typical design to 7.0 ns, indicating that the application of compositional grading can improve crystal quality and the interface becomes smoother, thus reducing the nonradiative recombination losses. Both the short-circuit current and open-circuit voltage are increased correspondingly and the conversion efficiency is improved from 14.57% of the typical design to 15.32% of the new p-emitter/window configuration under one-sun air-mass 1.5 global illumination. (C) 2010 The Japan Society of Applied Physics
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
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Han, Hau-Vei
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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.
Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate
(2019-02-14)
Chen, Sung-Wen Huang
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Wang, Sheng-Wen
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Hong, Kuo-Bin
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Medin, Henry
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Chung, Chieh-Han
In the present study, novel MoS2 bilayers with 3D structures were considered for their application as wavelength-sensitive photodetectors. Using e-gun deposition and a CVD process, MoS2 bilayers can be grown conformally on a patterned (cones or pyramids) sapphire substrate without any wrinkles on the 2D film. After the sulfurization process, the MoS2 bilayer is subjected to a local strain in the patterns and its band gap gets enlarged due to the strain. This phenomenon is beneficial for photo-devices to enable the collection of the photocurrent. Measurements revealed a broadband enhancement of the MoS2-based photodetector with a patterned array in terms of both absorption and photocurrent. It is noteworthy that a cone-patterned sapphire substrate (CPSS) is able to generate more photocurrent when illuminated under blue light illumination, whereas the pyramid-patterned sapphire substrate (PPSS) performs best under green and red light illumination. Simulations of the electric field distributions for MoS2 coatings on different substrates, based on 3D models, revealed that the sensitivity of the MoS2-based photodetector can be greatly enhanced by the light-scattering effect.
Epitaxial growth of semipolar InN(10(1)over-tilde3) on LaAlO3 substrate: Epitaxial relationship analysis
(2017-05-01)
Chen, Wei-Chun
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Kuo, Shou-Yi
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Tian, Jr. -Sheng
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Wang, Wei-Lin
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Lai, Fang-I
Epitaxial semipolar InN(10 (1) over tilde3) crystals were grown on a LaAlO3(112) substrate using radio frequency plasma-assisted molecular beam epitaxy without any interlayer. The lattice mismatch between InN and LaAlO3 was estimated to be % 7.75% along the [1 (2) over tilde 10](InN) direction and 0.2% along the [(3) over tilde 032](InN) direction. The InN film is epitaxic with the LaAlO3 substrate, with orientation relationships between InN(10 (1) over tilde3) parallel to LaAlO3(112) and [1 (2) over tilde 10](InN) parallel to [11 (1) over tilde](LAO). InN grown on LaAlO3(112) appears (10 (1) over tilde3) plane orientated, with two types of domains. Semipolar InN(10 (1) over tilde3) layers can be grown at 510 degrees C and show X-ray rocking curve FWHMs of 1830 and 1408 arcsec for InN(0002) and InN(10 (1) over tilde3), respectively. However, InN grown at 510 degrees C has the highest peak intensity and the narrowest FWHM of the prepared samples, indicating high-quality crystal growth. (C) 2017 The Japan Society of Applied Physics
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
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Han, Hau-Vei
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Lai, Fang-I
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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
Heteroepitaxial growth of InN on GaN intermediate layer by PA-MOMBE
(2011-07-01)
Lai, Fang-I
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Kuo, Shou-Yi
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Chen, Wei-Chun
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Lin, Woei-Tyng
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Wang, Wei-Lin
In this paper, high-quality wurtzite indium nitride was epi-grown on sapphire substrates by plasma-assisted metal-organic molecule beam epitaxy system (PA-MOMBE). Structural and electrical properties of the InN films were significantly improved by employing a GaN buffer layer. In addition, high-resolution X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), Hall Effect, Raman and photoluminescence spectroscopy were carried out to characterize the effect of the growth temperature on structural and optoelectronic properties. It was found that highly c-axis oriented InN epilayer can be obtained by optimizing growth conditions. TEM images reveal that the epitaxially grown InN/GaN interface is sharp, and the spacing of the InN(0 0 0 2) lattice plane is about 0.57 nm. Raman spectra also show a sharp peak at 491 cm(-1) attributed to the E(2)(high) mode of wurtzite InN. These results indicate that the improvement of InN material quality can be achieved using heteroepitaxy on GaN/sapphire templates. (C) 2011 Elsevier B.V. All rights reserved.
High extraction efficiency GaN-based light-emitting diodes on embedded SiO(2) nanorod array and nanoscale patterned sapphire substrate
(2010-06-28)
Huang, Hung-Wen
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Huang, Jhi-Kai
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Kuo, Shou-Yi
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Lee, Kang-Yuan
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Kuo, Hao-Chung
In this paper, GaN-based LEDs with a nanoscale patterned sapphire substrate (NPSS) and a SiO(2) photonic quasicrystal (PQC) structure on an n-GaN layer using nanoimprint lithography are fabricated and investigated. The light output power of LED with a NPSS and a SiO(2) PQC structure on an n-GaN layer was 48% greater than that of conventional LED. Strong enhancement in output power is attributed to better epitaxial quality and higher reflectance resulted from NPSS and PQC structures. Transmission electron microscopy images reveal that threading dislocations are blocked or bended in the vicinities of NPSS layer. These results provide promising potential to increase output power for commercial light emitting devices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456385]
High extraction efficiency GaN-based light-emitting diodes on embedded SiO2 nanorod array and nanoscale patterned sapphire substrate
(2010-06-28)
Huang, Hung-Wen
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Huang, Jhi-Kai
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Kuo, Shou-Yi
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Lee, Kang-Yuan
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Kuo, Hao-Chung
In this paper, GaN-based LEDs with a nanoscale patterned sapphire substrate (NPSS) and a SiO2 photonic quasicrystal (PQC) structure on an n-GaN layer using nanoimprint lithography are fabricated and investigated. The light output power of LED with a NPSS and a SiO2 PQC structure on an n-GaN layer was 48% greater than that of conventional LED. Strong enhancement in output power is attributed to better epitaxial quality and higher reflectance resulted from NPSS and PQC structures. Transmission electron microscopy images reveal that threading dislocations are blocked or bended in the vicinities of NPSS layer. These results provide promising potential to increase output power for commercial light emitting devices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456385]
Highly Efficient Flexible Hybrid Nanocrystal-Cu(In,Ga)Se-2 (CIGS) Solar Cells
(2015-01-21)
Liao, Yu-Kuang
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Brossard, Mael
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Hsieh, Dan-Hua
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Lin, Tzu-Neng
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Charlton, Martin D. B.
A novel scheme for hybridizing inkjet-printed thin film Cu(In,Ga)Se-2 (CIGS) solar cells with self-assembled clusters of nanocrystal quantum dots (NQDs), which provides a 10.9% relative enhancement of the photon conversion efficiency (PCE), is demonstrated. A non-uniform layer of NQD aggregates is deposited between the transparent conductive oxide and a CdS/CIGS p-n junction using low cost pulsed-spray deposition. Hybridization significantly improves the external quantum efficiency of the hybrid devices in the absorption range of the NQDs and in the red to near-IR parts of the spectrum. The low wavelength response enhancement is found to be induced by luminescent down-shifting (LDS) from the NQD layer, while the increase at longer wavelengths is attributed to internal scattering from NQD aggregates. LDS is demonstrated using time-resolved spectroscopy, and the morphology of the NQD layer is investigated in fluorescence microscopy and cross-sectional transmission electron microscopy. The influence of the NQD dose on the PCE of the hybrid devices is investigated and an optimum value is obtained. The low costs and limited material consumptions associated with pulsed-spray deposition make these flexible hybrid devices promising candidates to help push thin-film photovoltaic technology towards grid parity.
Influence of V/III Flow Ratio on Growth of InN on GaN by PA-MOMBE
(2013)
Chen, Wei-Chun
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Tian, Jr-Sheng
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Wu, Yue-Han
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Wang, Wei-Lin
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Kuo, Shou-Yi
InN epilayers were prepared on c-GaN/sapphire substrates by plasma-assisted metal-organic molecular beam epitaxy using N-2 and trimethylindium precursor as the V/III sources. We studied the influence of the V/III flow ratio on the film structure, surface morphology, film compositions, and optical and electrical properties using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), photoluminescence (PL) measurement and Hall effect. The results show that epitaxial InN films can be obtained with the V/III ratio in the range between 1.81 and 4 at 500 degrees C. The InN growth rate decreases from 1.9 to 1.4 mu m/h when the ratio increases from 1.81 to 4. The surfaces of the InN films are not smooth in the V/III range used. Cross-sectional TEM revealed that the planar defect density in InN is as high as similar to 1.5 x 10(6) cm(-1) at a V/III ratio of similar to 1.81. XPS and SIMS results show that the film surface contains oxygen, which is found to affect the measured carrier mobility and concentration. (C) 2013 The Electrochemical Society. All rights reserved.
Investigation and Comparison of the GaN-Based Light-Emitting Diodes Grown on High Aspect Ratio Nano-Cone and General Micro-Cone Patterned Sapphire Substrate
(2013-12-01)
Huang, Jhih-Kai
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Lin, Da-Wei
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Shih, Min-Hsiung
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Lee, Kang-Yuan
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Chen, Jyun-Rong
In this paper, we demonstrated the high performance GaN-based LEDs by using a high aspect ratio cone-shape nano-patterned sapphire substrate (HAR-NPSS). We utilized nano-imprint lithography (NIL) and dry-etching system to fabricate a high depth HAR-NPSS. The micro-scale patterned sapphire substrate (PSS) was also used for comparison. A great enhancement of light output was observed when GaN-based LEDs were grown on a HAR-NPSS or a PSS. The light output power of LEDs with a HAR-NPSS and LEDs with a PSS were enhanced of 49 and 38% compared to LEDs with a unpatterned sapphire substrate. The high output power of the LED with a HAR-NPSS indicated that the technology of NAR-NPSS not only can improve the crystalline quality of GaN-based LEDs but also a promising development to a NPSS.
Investigation of Cu-Zn Point Defect on the Photovaltaic Performance of the RF-Sputtered Cu2ZnSnSe4-Based Thin Film Solar Cell
(2013-01-01)
Kuo, Shou-Yi
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Hsieh, Dan-Hua
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Yanga, Jui-Fu
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Lai, Fang-I
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Kuo, Hao-Chung
A 4.4 % RF-sputtered Cu2ZnSnSe4 thin film solar cell was studied by transmittance electron microscopy (TEM) and photoluminescence (PL). The result reveals non-uniform elemental distribution and large potential fluctuation mainly induced by Cu-Zn defect.