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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
;
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.
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
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
Patterned structure of REMOTE PHOSPHOR for phosphor-converted white LEDs
(2011-07-04)
Kuo, Hao-Chung
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Hung, Cheng-Wei
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Chen, Hsin-Chu
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Chen, Kuo-Ju
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Wang, Chao-Hsun
High efficiency white light-emitting diodes with superior color-mixing have been investigated. It is suggested that the patterned remote phosphor structure could improve the uniformity of angular-dependent correlated color temperature (CCT) and achieve high chromatic stability in wider operating current range, as compared to the conventional remote phosphor coating structure. In this experiment, we employed a pulse spray coating method to place the patterned phosphor on the package and to leave a window region. The window area, a clear space without coating of the phosphor not only increases the extraction efficiency of blue rays at large angle, but also improves the stability of angular-dependent CCT. Moreover, the CCT deviation could be reduced from 1320 K to 266 K by this patterned remote phosphor method, and the stray blue/yellow light within the package can be effectively reduced and controlled. The design was verified both experimentally and theoretically. (C) 2011 Optical Society of America
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
White light emitting diodes with enhanced CCT uniformity and luminous flux using ZrO2 nanoparticles
(2014)
Chen, Kuo-Ju
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Han, Hau-Vei
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Chen, Hsin-Chu
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Lin, Chien-Chung
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Chien, Shih-Hsuan
To enhance the uniformity of correlated color temperature (CCT) and luminous flux, we integrated ZrO2 nanoparticles into white light-emitting diodes. This novel packaging scheme led to a more than 12% increase in luminous flux as compared to that in conventional dispensing structures. This was attributed to the scattering effect of ZrO2 nanoparticles, which enhanced the utilization of blue light. Moreover, the CCT deviation was reduced from 522 to 7 K in a range of -70 to +70 degrees, and essentially eliminated the yellow ring phenomenon. The haze measurement indicated strong scattering across the visible spectrum in the presence of ZrO2 in the silicone layer, and this finding also substantiates our claim. In addition, the chromaticity coordinate shift was steady in the ZrO2 dispensing package structure as the drive current increased, which is crucial for indoor lighting. Combined with its low cost, easy fabrication, and superior optical characteristics, ZrO2 nanoparticles can be an effective performance enhancer for the future generation of white light-emitting devices.
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.
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.
Improving efficiency of InGaN/GaN multiple quantum well solar cells using CdS quantum dots and distributed Bragg reflectors
(2013-10-01)
Tsai, Yu-Lin
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Lin, Chien-Chung
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Han, Hau-Vei
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Chang, Chun-Kai
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Chen, Hsin-Chu
This work demonstrates hybrid InGaN/GaN multiple quantum well (MQW) solar cells with enhanced power conversion efficiency using colloidal CdS quantum dots (QDs) and back-side distributed Bragg reflectors (DBRs). CdS QDs can absorb ultraviolet (UV) photons, which are strongly absorbed by indium tin oxide (ITO), and they emit photons with a longer wavelength. This process improves the collection of photon-generated carriers and is known as the luminescence down-shifting (LDS). Accordingly, CdS QDs can compensate for the poor utilization of UV photons in an ITO layer, enhancing the external quantum efficiency (EQE) in the UV range. The DBRs on the back of the solar cells can reflect photons of longer wavelengths back into the absorber layer, increasing the EQE (380-440 nm). The combination of CdS QDs and DBRs results in broadband EQE enhancement, and yields an overall power conversion efficiency that is 20.7% better than that of a reference device without CdS QDs and DBRs. (C) 2013 Elsevier B.V. All rights reserved.
Improving the Angular Color Uniformity of Hybrid Phosphor Structures in White Light-Emitting Diodes
(2013-10-01)
Chen, Kuo-Ju
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Han, Hau-Vei
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Lin, Bing-Cheng
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Chen, Hsin-Chu
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Shih, Min-Hsiung
This letter examines a hybrid phosphor structure for white light-emitting diodes. The hybrid phosphor structure produces more efficient luminosity and more uniform angular correlated color temperature (CCT) than the conventional dispensing method. The experimental results show that the CCT deviation improved from 453 to 280 K between -70 degrees and 70 degrees. This was likely caused by the large blue light divergent angle. The lumen output produced was higher than that produced by dispense and conformal phosphor structures. Therefore, the results show that the hybrid phosphor structure can be used in solid-state lighting.

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