Browsing by Author "Lai, Fang-I"

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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
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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.
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
Beam profile characteristics of InGaAs sub-monolayer quantum-dot photonic-crystal VCSELs
(2007-06-01)
Yang, Hung-Pin D.
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Hsu, I-Chen
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Lai, Fang-I
;
Lin, Gray
;
Hsiao, Ru-Shang
An InGaAs sub-monolayer (SML) quantum dot photonic crystal vertical-cavity surface-emitting laser (QD PhC-VCSEL) for fiberoptic applications is first time demonstrated. The active region of the device contains 3 InGaAs SML QD layers. Each of the InGaAs SML QD layer is formed by alternate deposition of InAs (< 1 ML) and GaAs. Single fundamental mode CW output power of 3.8 mW at 28 mA has been achieved in the 990 nm range, with a threshold current of 0.9 mA. Side-mode suppression ratio (SMSR) larger than 35 dB has been demonstrated over entire current operation range. The beam profile study of the PhC-VCSEL indicates that the laser beam is well confined by the photonic crystal structure of the device. The divergence angle of the devices remains almost unchanged with increasing current. (C) 2007 Elsevier B.V. All rights reserved.
Characteristics of broad-area InGaAs submonolayer quantum-dot vertical-cavity surface-emitting lasers
(2007-10-01)
Yang, Hung-Pin D.
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Hsu, I-Chen
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Lai, Fang-I
;
Lin, Gray
;
Hsiao, Ru-Shang
A broad-area InGaAs submonolayer (SML) quantum-dot vertical-cavity surface-emitting laser (QD VCSEL) for fiber-optic applications is demonstrated. The active region of the device contains three InGaAs SML QD layers. Each of the InGaAs SML QD layers is formed by alternate depositions of InAs (< 1 ML) and GaAs. A maximum CW output power of 12.2 mW at 30 mA has been achieved in the 990 nm range, with a threshold current of 1 mA.
Characteristics of cross-shaped polarization-switching vertical-cavity surface-emitting lasers for dual-channel communications
(2007-04-01)
Yang, Hung-Pin D.
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Hsu, I-Chen
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Lai, Fang-I
;
Lin, Gray
;
Kuo, Hao-Chung
The polarization switching of a cross-shaped vertical-cavity surface-emitting laser (VCSEL) for dual-channel communications is demonstrated. The polarization of the lasing output is controlled by the asymmetry in geometry of the device and direction of current injection. High output power ratio of over 5, between two orthogonal (perpendicular) polarization directions has been achieved. The lasing output of the device can be switched between two nearly orthogonal directions.
Characteristics of InGaAs submonolayer quantum-dot and InAs quantum-dot photonic-crystal vertical-cavity surface-emitting lasers
(2008-05-01)
Yang, Hung-Pin D.
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Hsu, I. -Chen
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Chang, Ya-Hsien
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Lai, Fang-I
;
Yu, Hsin-Chieh
We have made InGaAs submonolayer (SML) quantum-dot (QD) and InAs QD photonic-crystal vertical-cavity surface-emitting lasers (PhC-VCSELs) for fiber-optic communications in the 990 and 1300 nm ranges, respectively. The active region of the InGaAs SML QD PhC-VCSEL contains three InGaAs SML QD layers, with each of the SML QD layer formed by alternating depositions of InAs (< 1 ML) and GaAs. The active region of the InAs QD PhC-VCSEL contains 17 undoped InAs-InGaAs QD layers. Both types of QD PhC-VCSELs exhibit single-mode characteristics throughout the current range, with side-mode suppression ratio (SMSR) larger than 35 dB. A maximum output power of 5.7 mW has been achieved for the InGaAs SML QD PhC-VCSEL. The near-field image study of the QD PhC-VCSELs indicates that the laser beam is well confined by the photonic-crystal structure of the device.
Characteristics of multileaf holey light-emitting diodes for fiber-optic communications
(2008-02-01)
Yang, Hung-Pin D.
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Yeh, Zao-En
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Lai, Fang-I
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Kuo, Hao-Chung
;
Chi, Jim Y.
An oxide-confined multileaf holey light-emitting diode (LED) in the 780 nm range is reported. The device is consisted of bottom distributed Bragg reflector (DBR), quantum wells QWs), and top DBR, with a multileaf holey structure within the p-ohmic contact ring for light extraction. The spontaneous emission from under the etched holes and internally reflected lights can be extracted and collimated out of the smaller etched leaf holes. High-resolution imaging studies indicate that the device emits with smaller beams mainly through the multileaf etched holes made it suitable for fiber-optic communications.
Characteristics of P-substrate small-aperture holey light-emitting diodes for fiber-optic applications
(2007-05-01)
Yang, Hung-Pin D.
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Liu, Jui-Nung
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Lai, Fang-I
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Kuo, Hao-Chung
;
Chi, Jim Y.
A small-aperture oxide-confined holey light-emitting diode (LED) on p-type GaAs substrate in the 830 nm range is reported. The device is consisted of bottom distributed Bragg reflector (DBR), quantum wells (QWs), and top DBR, with a small-aperture holey structure at the center for light extraction. The internally reflected spontaneous emission can be extracted and collimated out of the etched hole. High-resolution imaging studies indicate that the device emits with a narrower beam mainly through the central etched hole region made it suitable for fiber-optic applications.
Characteristics of single-mode InGaAs submonolayer quantum-dot photonic-crystal vertical-cavity surface-emitting lasers
(2006-12-01)
Yang, Hung-Pin D.
;
Hsu, I-Chen
;
Lai, Fang-I
;
Lin, Gray
;
Hsiao, Ru-Shang
An InGaAs submonolayer (SML) quantum-dot photonic-crystal vertical-cavity surface-emitting laser (QD PhC-VCSEL) for fiber-optic applications is demonstrated for the first time. The active region of the device contains three InGaAs SML QD layers. Each of the InGaAs SML QD layers is formed by alternate depositions of InAs (< 1 ML) and GaAs. A single-fundamental-mode CW output power of 3.8 mW at 28 mA has been achieved in the 990 nm range, with a threshold current of 0.9 mA. A side-mode suppression ratio (SMSR) larger than 35 dB has been demonstrated over the entire current operation range. The beam profile and near-field image study of the PhC-VCSEL indicates that the laser beam,is well confined by the photonic crystal structure of the device.
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.
Crystalline Engineering Toward Large-Scale High-Efficiency Printable Cu(In,Ga)Se-2 Thin Film Solar Cells on Flexible Substrate by Femtosecond Laser Annealing Process
(2017-04-26)
Chen, Shih-Chen
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She, Nian-Zu
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Wu, Kaung-Hsiung
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Chen, Yu-Ze
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Lin, Wei-Sheng
Ink-printing method emerges as a viable way for manufacturing large-scale flexible Cu(In,Ga)Se-2 (CIGS) thin film photovoltaic (TFPV) devices owing to its potential for the rapid process, mass production, and low-cost nonvacuum device fabrication. Here, we brought the femtosecond laser annealing (fs-LA) process into the ink-printing CIGS thin film preparation. The effects of fs-LA treatment on the structural and optoelectronic properties of the ink-printing CIGS thin films were systematically investigated. It was observed that, while the film surface morphology remained essentially unchanged under superheating, the quality of crystallinity was significantly enhanced after the fs-LA treatment. Moreover, a better stoichiometric composition was achieved with an optimized laser scanning rate of the laser beam, presumably due to the much reduced indium segregation phenomena, which is believed to be beneficial in decreasing the defect states of In-se, V-Se, and In-cu. Consequently, the shunt leakage current and recombination centers were enhancement in photovoltaic conversion efficiency. both greatly decreased, resulting in a near 20%
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.
Design and fabrication of temperature-insensitive InGaP-InGaAlP resonant-cavity light-emitting diodes
(2006-07-01)
Chang, Yi-An
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Yu, Chun-Lung
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Wu, I-Tsung
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Kuo, Hao-Chung
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Lu, Tien-Chang
Visible InGaP-InGaAlP resonant-cavity light-emitting diodes with low-temperature sensitivity output characteristics were demonstrated. By means of widening the resonant cavity to a thickness of three wavelength (3 A), the degree of power variation between 25 degrees C and 95 degrees C for the devices biased at 20 mA was apparently reduced from -2.1 dB for the standard structure design (1 - lambda avity) to -0.6 dB. An output power of 2.4 mW was achieved at 70 mA. The external quantum efficiency achieved a maximum of 3% at 13 mA and dropped slowly with increased current for the device. The external quantum efficiency at 20 mA dropped only 14% with elevated temperature from 25 degrees C to 95 degrees C. The current dependent far-field patterns also showed that the emission always took place perfectly in the normal direction, which was suitable for plastic fiber data transmission.
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.
Effect of nitrogen contents on the temperature dependence of photoluminescence in InGaAsN/GaAs single quantum wells
(2006-07-01)
Lai, Fang-I
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Kuo, S. Y.
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Wang, J. S.
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Kuo, H. C.
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Wang, S. C.
A series of InGaAsN/GaAs single-quantum wells (SQWs) with N contents varied from 0% to 5.3% were grown by molecular-beam epitaxy using a solid As and a nitrogen plasma sources. The impact of nitrogen concentration on the optical properties, as determined by the temperature dependence of photoluminescence (PL), of a 6 nm SQW was investigated. In the low-temperature region, a pronounced temperature-dependent S-shaped peak position was observed in PL spectra while increasing the nitrogen concentration. Quenching behavior reveals that the defect-related nonradiative processes might be enhanced in the highly nitrogen incorporated samples and thus influence the recombination dynamics. In addition, the evolution of the peak position of the InGaAsN/GaAs samples was in agreement with the empirical Varshni model in the high-temperature region. A significant reduction in the temperature dependence of the emission peak position is analyzed as well, and further confirms the prediction of proposed band anticrossing model of the electronic structure of III-N-V alloys. (c) 2006 American Vacuum Society.
Efficiency enhancement of InGaN/GaN multiple quantum well solar cells using CdS quantum dots and distributed Bragg reflectors
(2013)
Tsai, Yu-Lin
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Lin, Chien-Chung
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Han, Hau-Vei
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Chen, Hsin-Chu
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Chen, Kuo-Ju
In recent year, InGaN-based alloy was also considered for photovoltaic devices owing to the distinctive material properties which are benefit photovoltaic performance. However, the Indium tin oxide (ITO) layer on top, which plays a role of transparent conductive oxide (TCO), can absorb UV photons without generating photocurrent. Also, the thin absorber layer in the device, which is consequent result after compromising with limited crystal quality, has caused insufficient light absorption. In this report, we propose an approach for solving these problems. A hybrid design of InGaN/GaN multiple quantum wells (MQWs) solar cells combined with colloidal CdS quantum dots (QDs) and back side distributed Bragg reflectors (DBRs) has been demonstrated. CdS QDs provide down-conversion effect at UV regime to avoid absorption of ITO. Moreover, CdS QDs also exhibit anti-reflective feature. DBRs at the back side have effectively reflected the light back into the absorber layer. CdS QDs enhance the external quantum efficiency (EQE) for light with wavelength shorter than 400 nm, while DBRs provide a broad band enhancement in EQE, especially within the region of 400 nm similar to 430 nm in wavelength. CdS QDs effectively achieved a power conversion efficiency enhancement as high as 7.2% compared to the device without assistance of CdS QDs. With the participation of DBRs, the power conversion efficiency enhancement has been further boosted to 14%. We believe that the hybrid design of InGaN/GaN MQWs solar cells with QDs and DBRs can be a method for high efficiency InGaN/GaN MQWs solar cells.
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
;
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
;
Yang, Jui-Fu
;
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 Light Extraction Efficiency of GaN-Based Hybrid Nanorods Light-Emitting Diodes
(2015-07-01)
Huang, Jhih-Kai
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Liu, Che-Yu
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Chen, Tzi-Pei
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Huang, Hung-Wen
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Lai, Fang-I
High light extraction GaN-based light-emitting diodes (LEDs) with a hybrid structure of straight nanorods located in an array of microholes have been successfully demonstrated. Via the nanoimprint lithography and photolithography techniques, high aspect-ratio light-guiding InGaN/GaN nanorods can be fabricated and regularly arranged in microholes, resulting in a great improvement of the light extraction for the GaN-based LED device. The light output power of the hybrid nanorods LED is 22.04 mW at the driving current standard of 25.4 A/cm(2), an enhancement of 38.7% to the conventional GaN-based LEDs. Furthermore, with a modification of the hybrid structures\' dimensions and locations, the emitted optical energy can be redistributed to obtain light-emitting devices with homogenueous optical field distributions.