Browsing by Author "Han, Hau-Vei"

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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.
Advantages of Blue LEDs With Graded-Composition AlGaN/GaN Superlattice EBL
(2013-11-01)
Lin, Bing-Cheng
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Chen, Kuo-Ju
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Han, Hau-Vei
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Lan, Yu-Pin
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Chiu, Ching-Hsueh
InGaN/GaN light-emitting diodes (LEDs) with graded-composition AlGaN/GaN superlattice (SL) electron blocking layer (EBL) were designed and grown by metal-organic chemical vapor deposition. The simulation results demonstrated that the LED with a graded-composition AlGaN/GaN SL EBL have superior hole injection efficiency and lower electron leakage over the LED with a conventional AlGaN EBL or normal AlGaN/GaN SL EBL. Therefore, the efficiency droop can be alleviated to be similar to 20% from maximum at an injection current of 15-120 mA, which is smaller than that for conventional AlGaN EBL (30%). The corresponding experimental results also confirm that the use of a graded-composition AlGaN/GaN SL EBL can markedly enhance the light output power by 60%.
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.
Compound biomimetic structures for efficiency enhancement of Ga0.5In0.5P/GaAs/Ge triple-junction solar cells
(2014-03-10)
Hung, Mu-Min
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Han, Hau-Vei
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Hong, Chung-Yu
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Hong, Kuo-Hsuan
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Yang, Tung-Ting
Biomimetic nanostructures have shown to enhance the optical absorption of Ga0.5In0.5P/GaAs/Ge triple junction solar cells due to excellent antireflective (AR) properties that, however, are highly dependent on their geometric dimensions. In practice, it is challenging to control fabrication conditions which produce nanostructures in ideal periodic arrangements and with tapered side-wall profiles, leading to sacrificed AR properties and solar cell performance. In this work, we introduce compound biomimetic nanostructures created by depositing a layer of silicon dioxide (SiO2) on top of titanium dioxide(TiO2) nanostructures for triple junction solar cells. The device exhibits photogenerated current and power conversion efficiency that are enhanced by similar to 8.9% and similar to 6.4%, respectively, after deposition due to their improved antireflection characteristics. We further investigate and verify the optical properties of compound structures via a rigorous coupled wave analysis model. The additional SiO2 layer not only improves the geometric profile, but also serves as a double-layer dielectric coating. It is concluded that the compound biomimetic nanostructures exhibit superior AR properties that are relatively insensitive to fabrication constraints. Therefore, the compound approach can be widely adopted for versatile optoelectronic devices and applications. (C)2014 Optical Society of America
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.
Efficiency and droop improvement in green InGaN/GaN light-emitting diodes on GaN nanorods template with SiO2 nanomasks
(2012-12-03)
Lin, Da-Wei
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Lee, Chia-Yu
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Liu, Che-Yu
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Han, Hau-Vei
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Lan, Yu-Pin
This study presents the green InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) grown on a GaN nanorods template with SiO2 nanomasks by metal-organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth, microscale air voids were formed between nanorods and the threading dislocations were efficiently suppressed. The electroluminescence measurement reveals that the LEDs on nanorods template with SiO2 nanomasks suffer less quantum-confined Stark effect and exhibit higher light output power and lower efficiency droop at a high injection current as compared with conventional LEDs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768950]
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.
Embedded InN Dot-Like Structure within InGaN Layers Using Gradient-Indium Content in Nitride-Based Solar Cell
(2013)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Tan, Ming-Hsuan
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Yeh, Yun-Ling
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Lin, Da-Wei
The novel design of embedded InN dot-like structure within InGaN was useful as an absorption layer in photovoltaic (PV) cells. We constructed the simulation model by employing the commercial software APSYS (R) and integrating the absorption coefficient of thin InN materials fabricated by metal organic vapor deposition (MOCVD). The model of simulating gradient Indium content of InGaN used as transition interface between InN and GaN was investigated. The results exhibit utilizing the effective variation of Indium content and suitable thickness to approach the optimal characteristic of hybrid InN/InGaN structure within solar cells shall be anticipated to enhance the performance of current nitride-based solar cells.
Embedded InN Dot-Like Structures with Modulating Growth Temperature in Nitride-Based Solar Cell
(2014-01-01)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Da-Wei
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Kuo, Hao-Chung
The embedded InN dot-like structures within nitride-based solar cells is promising for extended visible and infrared absorption of solar spectrum. The temperature dependent InN epitaxial growth was demonstrated in a low-pressure metal organic chemical vapor deposition (MOCVD) system and the absorption coefficient of fabricated InN-dots was measured and integrated into APSYS (R) simulation platform. The dimension-quantization effect of the InN dot-like layer was investigated via photoluminescence (PL) measurements. Higher growth temperature region induces multiple PL peaks and blue-shift phenomenon, which could be attributed to variations in size and composition. The extracted absorption coefficients of InN-dot-like layer can be used to calculate the conversion efficiency of 2.34% for the corresponding GaN-based solar cell design.
Enhance Current Density and Power Conversion Efficiency in Solar Cells by Using Luminescent Downshifting Phosphors
(2014-01-01)
Han, Hau-Vei
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Lin, Chien-Chung
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Lin, Wein-Yi
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Tsai, Yu-Lin
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Shen, Tien-Lin
The silicate phosphor on the surface of GaAs solar cell are demonstrated to have promising potential for efficient solar spectrum utilization. The phosphor is a common utilized material in white light LED package, so the cost of phosphor is relatively low and the stability is good. The solar cells showed an enhancement of 22.8% in short-circuit current density and approximately 25.3% in power conversion efficiency when coated with silicate phosphor particles. The current analyses and experiments conclude that the phosphor particles not only play as luminescent downshifting centers in the ultraviolet region but also serve as an anti-reflection coating for enhancing the light absorption in the overall spectral response of external quantum efficiency.
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 light harvesting of nitride-based nanopillars covered with ZnO using indium-tin oxide nanowhiskers
(2014-04-01)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Lee, Hsin-Ying
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Huang, Jhih-Kai
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Han, Hau-Vei
Nitride-based nanopillars were successfully fabricated by nanoimprint lithography. A nanowhisker of indium-tin oxide (ITO) deposited by on oblique evaporation method was investigated in nitride-based nanopillars and thin ZnO layers grown by atomic layer deposition (ALD). From the results of field-emission scanning electron microscopy (SEM) measurement, it was found that ITO whiskers grew on nitride-based nanopillars covered with ZnO. Moreover, from the results of UV-visible spectrophotometry and bidirectional reflectance distribution function (BRDF) measurements, it was found that this hybrid structure of ITO nanowhiskers above a ZnO medium enhanced the broadband and angle-independent antireflection in the range between 380 and 600nm. We used the hybrid design of the ITO/ZnO structure to achieve the lowest reflectance value between 3.8 and 10.9% in a quantum well absorption range. (C) 2014 The Japan Society of Applied Physics
Enhanced photocurrent of a nitride-based photodetector with InN dot-like structures
(2014-12-01)
Hsu, Lung-Hsing
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Da-Wei
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Lo, Yen-Hua
The InN dot-like layer was applied in the gallium nitride based material for the purpose of infrared photodetectors (PDs). This InN layer was grown by a low-pressure metal organic chemical vapor deposition technology under different growth temperatures. The X-ray diffraction patterns provide the information of crystal structure and the hexagonal orientation was detected. The Raman shifts and photoluminescence were also used to characterize the quality of InN film. Finally, the fabricated Schottky-type photodetector was tested under a solar simulator and a long-wavelength laser (lambda = 1550nm). The measurements show a highly linear relation between photo-generated currents and laser powers for the wavelength of 1550 nm. In the photonic detection range suitable for optical fiber communiation, a quantum efficiency of 9.2% can be observed. (C) 2014 Optical Society of America
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."
Excellent Color Quality of White-Light-Emitting Diodes by Embedding Quantum Dots in Polymers Material
(2016-01-01)
Lin, Huang-Yu
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Wang, Sheng-Wen
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Lin, Chien-Chung
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Chen, Kuo-Ju
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Han, Hau-Vei
This study employs the polyfluorene composite (called Green B) with several colors of quantum dots to generate the high-color-rendering index (CRI) white LEDs. The Green B polymer is a good candidate to manufacture the hybrid w-LED because of its good quantum efficacy. The hybrid w-LEDs are fabricated by the mixing of Green B with yellow quantum dots and red quantum dots or orange quantum dots to obtain the correlated color temperatures of 3500 and 5500 K. The use of the hybrid polymer/QDs w-LEDs is proved to be beneficial as QD w-LEDs can improve the CRI up to 90 in 3500 K. The luminous efficiency of such devices can be as high as 17.2l m/W.
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
High Efficiency GaN-based Light Emitting Diodes with Embedded Air Voids/SiO2 Nanomasks
(2012-01-01)
Chiu, Ching-Hsueh
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Da-Wei
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Chen, Yan-Hao
We fabricated high efficiency LEDs with embedded micro-scale air voids and SiO2 nanomask exhibit smaller reverse-bias current and great enhancement of the light output (65% at 20mA) compared with the conventional LEDs.
High efficiency GaN-based light-emitting diodes with embedded air voids/SiO(2) nanomasks
(2012-02-03)
Chiu, Ching-Hsueh
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Lin, Chien-Chung
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Han, Hau-Vei
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Liu, Che-Yu
;
Chen, Yan-Hao
In this paper, the high performance GaN-based light-emitting diodes (LEDs) with embedded microscale air voids and an SiO(2) nanomask by metal-organic chemical vapor deposition (MOCVD) were demonstrated. Microscale air voids and an SiO(2) nanomask were clearly observed at the interface between GaN nanorods (NRs) and the overgrown GaN layer by scanning electron microscopy (SEM). From the reflectance spectra we show strong reflectance differences due to the different refractive index gradient between the GaN grown on the nanotemplate and sapphire. It can increase the light extraction efficiency due to additional light scattering. The transmission electron microscopy (TEM) images show the threading dislocations were suppressed by nanoscale epitaxial lateral overgrowth (NELOG). The LEDs with embedded microscale air voids and an SiO(2) nanomask exhibit smaller reverse-bias current and large enhancement of the light output (65% at 20 mA) compared with conventional LEDs.
High efficiency GaN-based light-emitting diodes with embedded air voids/SiO2 nanomasks
(2012-02-03)
Chiu, Ching-Hsueh
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Lin, Chien-Chung
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Han, Hau-Vei
;
Liu, Che-Yu
;
Chen, Yan-Hao
In this paper, the high performance GaN-based light-emitting diodes (LEDs) with embedded microscale air voids and an SiO2 nanomask by metal-organic chemical vapor deposition (MOCVD) were demonstrated. Microscale air voids and an SiO2 nanomask were clearly observed at the interface between GaN nanorods (NRs) and the overgrown GaN layer by scanning electron microscopy (SEM). From the reflectance spectra we show strong reflectance differences due to the different refractive index gradient between the GaN grown on the nanotemplate and sapphire. It can increase the light extraction efficiency due to additional light scattering. The transmission electron microscopy (TEM) images show the threading dislocations were suppressed by nanoscale epitaxial lateral overgrowth (NELOG). The LEDs with embedded microscale air voids and an SiO2 nanomask exhibit smaller reverse-bias current and large enhancement of the light output (65% at 20 mA) compared with conventional LEDs.
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
;
Chen, Kuo-Ju
;
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.