Browsing by Author "Kao, Yu-Cheng"

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An efficient and stable photoelectrochemical system with 9% solar-to-hydrogen conversion efficiency via InGaP/GaAs double junction
(2019-11-21)
Varadhan, Purushothaman
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Fu, Hui-Chun
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Kao, Yu-Cheng
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Horng, Ray-Hua
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He, Jr-Hau
Despite III-V semiconductors demonstrating extraordinary solar-to-hydrogen (STH) conversion efficiencies, high cost and poor stability greatly impede their practical implementation in photoelectrochemical (PEC) water splitting applications. Here, we present a simple and efficient strategy for III-V-based photoelectrodes that functionally and spatially decouples the light harvesting component of the device from the electrolysis part that eliminates parasitic light absorption, reduces the cost, and enhances the stability without any compromise in efficiency. The monolithically integrated PEC cell was fabricated by an epitaxial lift-off and transfer of inversely grown InGaP/GaAs to a robust Ni-substrate and the resultant photoanode exhibits an STH efficiency of similar to 9% with stability similar to 150 h. Moreover, with the ability to access both sides of the device, we constructed a fully-integrated, unassisted-wireless "artificial leaf" system with an STH efficiency of similar to 6%. The excellent efficiency and stability achieved herein are attributed to the light harvesting/catalysis decoupling scheme, which concurrently improves the optical, electrical, and electrocatalytic characteristics.
Colloidal Quantum Dot Enhanced Dual-Junction Tandem Solar Cells
(2016-01-01)
Hsu, Shun-Chieh
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Kao, Yu-Cheng
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Han, Hau-Vei
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Kuo, Hao-Chung
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Horng, Ray-Hua
In this work, we demonstrate the the enhancement of two type hybrid QD dual-junction solar cell. The green QD520 sample, shows better performance than blue QD450 sample in current density and power conversion efficiency. The enhancement of short-circuit current and power conversion efficiency for green QD450 sample are 4.43% and 3.77% and the blue QD520 samples are 9.44% and 5.78%. For short wavelength, the enhancement can mainly be attributed to the photon downshift effect and antireflection, for long wavelength, it only the antireflection effect.
Effects of buffer layers and front electrode angles on the performance of In0.16Ga0.84As solar cells
(2016-01-01)
Horng, Ray-Hua
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Wu, Fan-Lei
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Ou, Sin-Liang
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Kao, Yu-Cheng
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Shih, Shan-Hui
Three buffer layers, that included 2-step, step-graded, and linear-graded layers, were designed to improve the performance of In0.16Ga0.84As solar cell. The In0.16Ga0.84As solar cells fabricated on these three buffer layers were denoted as 2S-cell, S-cell, and L-cell, respectively. The efficiencies of these three devices were 9.8%, 14.4%, and 16.3%, respectively. Obviously, the linear-graded buffer layer is most helpful to enhance the efficiency of In0.16Ga0.84As solar cell. Additionally, the front electrode angle of In0.16Ga0.84As solar cell was varied from 0 degrees to 90 degrees. When the angles were fixed at 0 degrees and 90 degrees, the devices possessed higher efficiencies of 16.3% and 16.6%, respectively.
Feasibility Study for Double Luminescent Down-shifting Effect in A Dual Junction Solar Cell
(2019-01-01)
Huang, Yu-Ming
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Cho, Yu-Yun
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Hsu, Shun-Chieh
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Kao, Sheng-Feng
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Shih, Hsiang-Yun
In this work, we discuss the feasibility of two color photons for boosting up the short-circuit current and power conversion efficiency in tandem solar cell. One of them is by luminescent down-shifting (LDS) effect, and the other one is the infrared light emitting diode at 820nm. The CdZnSeS/ZnS quantum dots are used in this study. It can convert ultra-violet photons to visible ones which could be efficiently transformed into electron-hole pairs. The infrared-radiation LED can increase photo-generated carriers of the bottom GaAs solar cell. Finally, short-circuit current would significantly increase from 10.46 mA/cm(2) to 13.81 mA/cm(2), and power conversion efficiency increase from 19.89 to 25.22%. This result shows the possible double-LDS effect for solar cell enhancement in the future.
Performance comparison of III-V//Si and III-V//InGaAs multi-junction solar cells fabricated by the combination of mechanical stacking and wire bonding
(2019-03-13)
Kao, Yu-Cheng
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Chou, Hao-Ming
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Hsu, Shun-Chieh
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Lin, Albert
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Lin, Chien-Chung
The integration of III-V and Si multi-junction solar cells as photovoltaic devices has been studied in order to achieve high photovoltaic conversion efficiency. However, large differences in the coefficients of thermal expansion and the lattice parameters of GaAs, Si, and InGaAs have made it difficult to obtain high-efficiency solar cells grown as epilayers on Si and InP substrates. In this paper, two types of devices, including GaInP/GaAs stacked on Si (GalnP/GaAs//Si) and GaInP/GaAs stacked on InGaAs (GaInP/GaAs//InGaAs), are fabricated via mechanical stacking and wire bonding technologies. Mechanically stacked GaInP/GaAs//Si and GaInP/GaAsllInGaAs triple-junction solar cells are prepared via glue bonding. Current-voltage measurements of the two samples are made at room temperature. The short-circuit current densities of the GaInP/GaAs//Si and GaInP/GaAs//InGaAs solar cells are 13.37 and 13.66 mA/cm(2), while the open-circuit voltages of these two samples are measured to be 2.71 and 2.52V, respectively. After bonding the GaInP/GaAs dual-junction with the Si and InGaAs solar cells, the conversion efficiency is relatively improved by 32.6% and 30.9%, respectively, compared to the efficiency of the GaInP/GaAs dual-junction solar cell alone. This study demonstrates the high potential of combining mechanical stacked with wire bonding and ITO films to achieve high conversion efficiency in solar cells with three or more junctions.
Performance enhancement of III-V multi-junction solar cells using indium-tin-oxide electrodes
(2016-08-01)
Kao, Yu-Cheng
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Ou, Sin-Liang
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Wu, Fan-Lei
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Horng, Ray-Hua
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電機學院
InGaP/GaAs dual-junction solar cells were prepared on p-type GaAs substrates by metalorganic chemical vapor deposition. Three types of front-side electrodes, which included AuGe/Au metal-finger, ITO-finger, and ITO-overcoated, were individually fabricated on the devices and denoted as samples A, B, and C, respectively. The thickness of ITO film is 200 nm, and its transmittance can reach 99% in the visible region. Based on the current density-voltage (J-V) measurement, the short-circuit current density (J(sc)) of samples A, B, and C are 8.13, 9.35, and 10.90 mA/cm(2), while the conversion efficiencies of these three samples are evaluated to be 15.45%, 18.14%, and 20.24%, respectively. This reveals that sample C possesses 31.0% enhancement in the conversion efficiency compared to that of sample A. Additionally, the series resistances (Rs) of samples A, B, and C are 21.43, 22.94, and 6.71 Omega-cm(2), respectively. The lowest Rs occurred in sample C can be attributed to the elimination of the lateral resistance between electrodes because this device was fabricated with the ITO-overcoated front-side electrode. In sample C, since the ITO front-side electrode can cover overall surface of the device, all regions on the sample surface can extract the electrons, leading to the highest J(sc). (C) 2016 Elsevier B.V. All rights reserved.
The Analysis of Dual-Junction Tandem Solar Cells Enhanced by Surface Dispensed Quantum Dots
(2018-09-01)
Hsu, Shun-Chieh
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Huang, Yu-Ming
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Kao, Yu-Cheng
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Kuo, Hao-Chung
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Horng, Ray-Hua
The luminescent down-shifting (LDS) effect of a colloidal quantum dot layer on a dual junction solar cell is explored and analyzed. A 5.47% enhancement of power conversion efficiency is recorded when green quantum dots are dispersed on device surface. The surface reflectance spectra before and after the quantum dot dispenses are necessary to decouple the different mechanisms between antireflective and LDS effects. A further deduction of formulation on the dual-junction device with antireflection and LDS effect is presented and as high as 44.6% of short-circuit current increase in the green quantum dot case can be attributed to the LDS effect according to our calculation.