Browsing by Author "Chen, Hsin-Chu"

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A Highly Efficient Hybrid GaAs Solar Cell Based on Colloidal-Quantum-Dot-Sensitization
(2014-07-18)
Han, Hau-Vei
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Lin, Chien-Chung
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Tsai, Yu-Lin
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Chen, Hsin-Chu
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Chen, Kuo-Ju
This paper presents a hybrid design, featuring a traditional GaAs-based solar cell combined with various colloidal quantum dots. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. The merits of using highly efficient semiconductor solar cells and colloidal quantum dots were seamlessly combined to increase overall power conversion efficiency. Several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency, were measured and analyzed to investigate the performance of this hybrid device. Offering antireflective features at long wavelengths and luminescent downshifting for high-energy photons, the quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65% compared with traditional GaAs-based devices. The evolution of weighted reflectance as a function of the dilution factor of QDs was investigated. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6% of the entire enhancement of photogenerated current.
An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure
(2013-11-01)
Chen, Kuo-Ju
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Chen, Hsin-Chu
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Lin, Chien-Chung
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Wang, Chao-Hsun
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Yeh, Chia-Chi
An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a (c) nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.
Angle-resolved characteristics of silicon photovoltaics with passivated conical-frustum nanostructures
(2011-09-01)
Tseng, Ping-Chen
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Yu, Peichen
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Chen, Hsin-Chu
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Tsai, Yu-Lin
;
Han, Hao-Wei
Passivation plays a critical role in silicon photovoltaics, yet how a passivation layer affects the optical characteristics of nano-patterned surfaces has rarely been discussed. In this paper, we demonstrate conical-frustum nanostructures fabricated on silicon solar cells using polystyrene colloidal lithography with various silicon-nitride (SiN(x)) passivation thicknesses. The omnidirectional and broadband antireflective characteristics were determined by utilizing angle-resolved reflectance spectroscopy. The conical-frustum arrays with a height of 550 nm and a SiN(x) thickness of 80 nm effectively suppressed the Fresnel reflection in the wavelength range from 400 to 1000 nm, up to an incidence angle of 60 degrees. As a result, the power conversion efficiency achieved was 13.39%, which showed a 9.13% enhancement compared to that of a conventional KOH-textured silicon cell. The external quantum efficiency measurements confirmed that the photocurrent was mostly contributed by the increased optical absorption in the near-infrared. The angular cell efficiencies were estimated and showed improvements over large angles of incidence. (C) 2011 Elsevier B.V. All rights reserved.
ANGLE-RESOLVED REFLECTANCE SPECTROSCOPY OF PASSIVATED TRAPEZOID-CORN NANOSTRUCTURES FOR CRYSTALLINE SILICON PHOTOVOLTAICS
(2010)
Tseng, Ping-Chen
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Chen, Hsin-Chu
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Tsai, Min-An
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Kuo, Hao-Chung
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Yu, Peichen
In this work, we demonstrate an omnidirectional and broadband antireflective nanostructures incorporating a silicon nitrides (SiNx) passivation layer. The antireflective trapezoid-cone nanostructures are fabricated on a silicon wafer using polystyrene colloidal lithography with 550nm in height and then passivated with SiNx in different thicknesses to serve as the antireflection layer for silicon photovoltaics. The angle-resolved reflectance spectroscopy reveals that the trapezoid-cone nanostructures with an 80-nm-thick SiNx passivation layer effectively suppressed the Fresnel reflection over a broad spectral range and large angle of incidence (AOI). The AM1.5g weighted reflectance from 400 nm to 1000 nm is as low as 4.2% at normal incidence and <9.5% up to an AOI of 60 degrees, which is much superior to a conventional textured silicon substrate with passivation.
Efficiency and Droop Improvement in Hybrid Warm White LEDs Using InGaN and AlGaInP High-Voltage LEDs
(2013-04-01)
Chen, Kuo-Ju
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Kuo, Hsuan-Ting
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Chiang, Yen-Chih
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Chen, Hsin-Chu
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Wang, Chao-Hsun
This study investigates the optical and electrical characteristics in hybrid warm white high-voltage light-emitting diodes (HV-LEDs). The luminous efficiency of the hybrid warm white LED in this study improved by 11% and 51%, compared to conventional cool and warm LEDs, respectively, solving the warm white gap in white LEDs. The efficiency droop of the hybrid warm white LED was reduced to 21.8% from 26.8% for the conventional cool white LED, and from 26.3% in the conventional warm white LED at 40 mA (35 A/cm(2)) the operated current. Furthermore, the color rendering index (CRI) and angular correlated color temperature (CCT) were analyzed, indicating a significant improvement in hybrid warm white HV-LEDs.
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.
Enhanced conversion efficiency of a crystalline silicon solar cell with frustum nanorod arrays
(2011-01-03)
Tsai, Min-An
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Tseng, Ping-Chen
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Chen, Hsin-Chu
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Kuo, Hao-Chung
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Yu, Peichen
Enhanced photoelectric conversion is demonstrated in a crystalline silicon (c-Si) solar cell with frustum nanorod arrays (FNAs), fabricated using colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the cell with FNAs improves the power conversion efficiency by nearly 30%, compared to a conventional wet-chemical-textured reference. The enhancement mostly arises from the superior antireflective properties for wavelengths between 400 nm and 1000 nm. In that spectral range, we show that photons gained by reflection reduction directly contribute to collected carriers without auxiliary losses due to nano-fabrication. Moreover, the omnidirectional antireflection of FNAs is also investigated using an angle-resolved reflectance spectroscopy. The dimensions of FNAs are further analyzed with numerical calculations based on Maxwell's equations. The optimized short-circuit current density achieves nearly 40 mA/cm(2), corresponding to a 16% enhancement compared to the conventional device. (C)2010 Optical Society of America
Enhanced conversion efficiency of a crystalline silicon solar cell with frustum nanorod arrays
(2011-01-01)
Tsai, Min-An
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Tseng, Ping-Chen
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Chen, Hsin-Chu
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Kuo, Hao-Chung
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Yu, Peichen
Enhanced photoelectric conversion is demonstrated in a crystalline silicon (c-Si) solar cell with frustum nanorod arrays (FNAs). The omnidirectional antireflection of FNAs is also investigated using an angle-resolved reflectance spectroscopy and simulated by RCWA method. (C) 2010 Optical Society of America
Enhanced efficiency for c-Si solar cell with nanopillar array via quantum dots layers
(2011-09-12)
Chen, Hsin-Chu
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Lin, Chien-Chung
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Han, Hao-Wei
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Tsai, Yu-Lin
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Chang, Chia-Hua
The enhanced efficiency of the crystalline silicon (c-Si) solar cell with nanopillar arrays (NPAs) was demonstrated by deployment of CdS quantum dots (QDs). The NPAs was fabricated by the colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the device with CdS QDs shows a 33% improvement of power conversion efficiency, compared with the one without QDs. For further investigation, the excitation spectrum of photoluminescence (PL), absorbance spectrum, current-voltage (I-V) characteristics, reflectance and external quantum efficiency of the device was measured and analyzed. It is noteworthy that the enhancement of efficiency could be attributed to the photon down-conversion, the antireflection, and the improved electrical property. (C) 2011 Optical Society of America
Enhanced Luminous Efficiency of WLEDs Using a Dual-Layer Structure of the Remote Phosphor Package
(2013-06-15)
Chen, Kuo-Ju
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Chen, Hsin-Chu
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Shih, Min-Hsiung
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Wang, Chao-Hsun
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Tsai, Hsin-Han
This study demonstrates how the insertion of a thin silicone layer into a dual-layer remote phosphor structure enhances light extraction in white light-emitting diodes (WLEDs). In the experiment, a dual-layer phosphor structure yielded a higher intensity of blue and yellow components than a conventional structure. Moreover, the lumen flux was 5% higher than a conventional remote phosphor package at the same correlated color temperature (CCT). Using a TFCalc32 simulation, the electric field intensity was calculated for different thicknesses of the dual-layer remote phosphor structures, and the enhanced use of blue rays was verified. Additionally, the dual-layer structure reduces chromaticity deviations as the driving current increases.
Enhancement of angular CCT by hybrid phosphor structure in White Light-emitting Diodes
(2013)
Chen, Kuo-Ju
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Chen, Hsin-Chu
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Shih, Min-Hsiung
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Wang, Chao Hsun
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Chien, Shih-Hsuan
The hybrid phosphor structure for white light-emitting diodes application was reported. It was demonstrated that the improvement of the luminous efficiency as well as the good uniform angular correlated color temperature (CCT) in hybrid phosphor structure compared with the conventional dispense method. The experimental results showed the CCT deviation was improved from 453K to 280K in the range of -70 to 70 degrees, which could be attributed to the large divergent angle of blue light. Moreover, the high lumen output was also achieved, as compared with dispense and conformal phosphor structures. Therefore, the experimental results indicated that the hybrid phosphor structure was feasible to use in the solid state lighting.
Enhancement of power conversion efficiency in GaAs solar cells with dual-layer quantum dots using flexible PDMS film
(2012-09-01)
Chen, Hsin-Chu
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Lin, Chien-Chung
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Han, Hau-Vei
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Chen, Kuo-Ju
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Tsai, Yu-Lin
"This study demonstrates the high performance of GaAs solar cells with dual-layer CdS quantum dots (QDs) carried by flexible polydimethylsiloxane (PDMS) film. Several parameters were enhanced, including the short circuit current, fill factor, and power conversion efficiency, which were measured under white light illumination similar to the solar spectrum. The flexible PDMS film was fabricated using the spin-coating technique, and was then used to embed dual-layer CdS QDs. Different concentrations of QDs were applied in this design to test the optimal combination. The proposed scheme enhances power conversion efficiency by 22%, compared to a GaAs solar cell without CdS QDs. The photon down-conversion capability in the ultraviolet (UV) range and additional antireflection capability in the longer visible-IR range were verified through the external quantum efficiency. (C) 2012 Elsevier B.V. All rights reserved."
High Performance of Double-layer Quantum Dots with PDMS Film for Novel GaAs Solar Cells
(2012)
Chen, Hsin-Chu
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Lin, Chien-Chung
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Han, Hau-Vei
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Chen, Kuo-Ju
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Tsai, Yu-Lin
This study demonstrates the high performance of GaAs solar cells with double-layer quantum dots carried by flexible PDMS film. Several parameters were enhanced. Different concentrations of QDs were also applied to test the optimal combination.
High thermal stability of correlated color temperature using current compensation in hybrid warm white high-voltage LEDs
(2013-03-11)
Chen, Kuo-Ju
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Kuo, Hsuan-Ting
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Chen, Hsin-Chu
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Shih, Min-Hsiung
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Wang, Chao-Hsun
This study experimentally and numerically examines the correlated color temperature (CCT) stability issue for hybrid warm white high-voltage light-emitting diodes (HV-LEDs) by using a current compensation method. This method could efficiently maintain the CCT stability factor at approximately 1.0 and yield greater color uniformity with Delta u'v' values ranging from 0.017 to 0.003 in CIE 1976 chromaticity coordinates. The simulation results show that the red chip intensity drop is the primary cause of CCT instability in the hybrid warm white system when the temperature increases. Therefore, Furthermore, results indicate that the relative lumen drop improves from 21% to 15% by using a current compensation method. (c) 2013 Optical Society of America
High Uniformity of Remote Phosphor Structure by ZrO2 Nano-particles for White LEDs
(2012)
Chen, Kuo-Ju
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Chen, Hsin-Chu
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Lin, Chien-Chung
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Wang, Chao-Hsun
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Tsai, Hsin-Han
High luminous efficiency and superior uniformity of angular-dependent correlated color temperature white light-emitting diodes have been investigated by ZrO2 nano-particales in remote phosphor structure due to the higher capability of light scattering.
High-quality Quantum-Dot-Based Full-Color Display Technology by Pulsed Spray Method
(2013)
Chen, Kuo-Ju
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Chen, Hsin-Chu
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Tsai, Kai-An
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Lin, Chien-Chung
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Tsai, Hsin-Han
We fabricated the colloidal quantum-dot light-emitting diodes (QDLEDs) with the HfO2/SiO2-distributed Bragg reflector (DBR) structure using a pulsed spray coating method. Moreover, pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device were demonstrated. The experimental results showed that the intensity of red, blue, and green (RGB) emissions exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increased the use in the UV optical pumping of RGB QDs. In this experiment, a pulsed spray coating method was crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film was used as the interface layer between each RGB color to avoid cross-contamination and self-assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remained constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures was observed in the integrated device. The resulting color gamut of the proposed QDLEDs covered an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high-quality display technology.
Highly efficient CdS-quantum-dot-sensitized GaAs solar cells
(2012-03-12)
Lin, Chien-Chung
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Chen, Hsin-Chu
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Tsai, Yu Lin
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Han, Hau-Vei
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Shih, Huai-Shiang
We demonstrate a hybrid design of traditional GaAs-based solar cell combined with colloidal CdS quantum dots. With anti-reflective feature at long wavelength and down-conversion at UV regime, the CdS quantum dot effectively enhance the overall power conversion efficiency by as high as 18.9% compared to traditional GaAs-based device. A more detailed study showed an increase of surface photoconductivity due to UV presence, and the fill factor of the solar cell can be improved accordingly. (C) 2012 Optical Society of America
Highly efficient CdS-quantum-dot-sensitized InGaN multiple quantum well solar cells
(2012)
Tsai, Yu Lin
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Chen, Hsin-Chu
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Lin, Chien-Chung
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Han, Hau-Vei
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Yu, Peichen
We demonstrate a hybrid design of InGaN/GaN multiple quantum well (MQW) solar cells combined with colloidal CdS quantum dots. With anti-reflective feature at long wavelength and down-conversion at UV regime, the CdS quantum dot effectively enhance the overall power conversion efficiency by as high as 7.2% compared to the no CdS quantum dots coated device.
Highly Efficient Multiple-Layer CdS Quantum Dot Sensitized III-V Solar Cells
(2014-02-01)
Lin, Chien-Chung
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Han, Hau-Vei
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Chen, Hsin-Chu
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Chen, Kuo-Ju
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Tsai, Yu-Lin
In this review, the concept of utilization of solar spectrum in order to increase the solar cell efficiency is discussed. Among the three mechanisms, down-shifting effect is investigated in detail. Organic dye, rare-earth minerals and quantum dots are three most popular down-shift materials. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. A multiple layer structure, including PDMS as the isolation layer, is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved and the optimized concentration can be found.
Improved efficiency for nanopillar array of c-Si photovoltaic by down-conversion and anti-reflection of quantum dots
(2012)
Lin, Chien-Chung
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Chen, Hsin-Chu
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Han, Hau-Vei
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Tsai, Yu-Lin
;
Chang, Chia-Hua
Improvement of efficiency for crystalline silicon (c-Si) with nanopillar arrays (NPAs) solar cell was demonstrated by deployment of CdS quantum dots (QDs). The NPAs was fabricated by colloidal lithography of self-assembled polystyrene (PS) nanospheres with a 600 nm in size and reactive-ion etching techniques, and then a colloidal CdS QDs with a concentration of 5 mg/mL was spun on the surface of c-Si with NPAs solar cell. Under a simulated one-sun condition, the device with CdS QDs shows a 33% improvement of power conversion efficiency, compared with the one without QDs. Additionally, we also found that the device with CdS QDs shows a 32% reduction in electrical resistance, compared with the one without QDs solar cell, under an ultraviolet (UV) light of 355nm illumination. This reduced electrical resistance can directly contribute to our fill-factor (FF) enhancement. For further investigation, the excitation spectrum of photoluminescence (PL), absorbance spectrum, current-voltage (I-V) characteristics, reflectance and external quantum efficiency (EQE) of the device were measured and analyzed. Based on the spectral response and optical measurement, we believe that CdS QDs not only have the capability for photon down-conversion in ultraviolet region, but also provide extra antireflection capability.