Browsing by Author "Yu, Peichen"

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10% Efficiency Hybrid GaAs/PEDOT:PSS Solar Cells with Monolayer Graphene
(2014-01-01)
Cheng, Kai-Yuan
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Pan, Huai-Te
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Yu, Shu-Cheng
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Weng, Wei-Sheng
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Lai, Yi-Chun
The development of solution-processed hybrid organic-inorganic heterojunction solar cells have provoked increasing research effort due to potential to significantly reduce the fabrication cost of semiconductor solar cells while maintaining the high power conversion efficiency (PCE). With a recent record of GaAs solar cells achieving 28.8% via a wafer lift-off technique, hybrid organic/GaAs solar cells can offer an alternative route to provide more affordable solar power than current semiconductor technologies. In this work, we demonstrate the hybrid devices based on a conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) directly spun-cast on planar gallium arsenide materials. While still lacking for optimized antireflection, the PCE of the best performing device can achieve nearly 10% by introducing the monolayer graphene as transparent electrode. The current progress presents 2-fold enhancement in comparison to a previous record at 5% based on GaAs nanowire templates.
11%-Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell with an Intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane Layer
(2013)
Tsai, Chia-Ying
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Chen, Po-Han
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Huang, Yang-Yue
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Pen, Huai-Te
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Yu, Peichen
Hybrid organic-inorganic heterojunction solar cells based on silicon nanowires (SiNWs) are promising candidates for next-generation photovoltaics owing to potentials for low fabrication cost and high efficiency. The SiNW array, fabricated by a simple metal-assisted wet chemical etching method, produces a large surface-area-to-volume ratio, hence allowing efficient light harvesting and charge collection via the formation of a core-sheath p-n junction. However, previously reported power conversion efficiencies (PCEs) are approximately capped at 10%, which is largely depicted by the interface defect densities that limit the open-circuit voltage (V-oc) and fill factor (FF). In this work, we introduce a solution-processed, intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) layer to mitigate the interface recombination loss for hybrid heterojunction solar cells consisted of SiNWs and conjugate polymer poly(3,4-ethylenedioxy-thiophene): poly(styrenesulfonate) (PEDOT:PSS). A record PCE of 11.0% is achieved in contrast to 9.6% from a reference counterpart without TAPC, which represents an enhancement factor of 14.2% ascribed to noticeable improvement in the V-oc and FF. The result is further supported by examining indicators for the interface quality via a suppressed dark saturation current and an enhanced minority carrier lifetime which exhibits an increase from 84 mu sec without TAPC to 87 mu sec with TAPC.
13% Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell via Interface Engineering
(2013-12-01)
Yu, Peichen
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Tsai, Chia-Ying
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Chang, Jan-Kai
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Lai, Chih-Chung
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Chen, Po-Han
Interface carrier recombination currently hinders the performance of hybrid organic silicon heterojunction solar cells for high-efficiency low-cost photovoltaics. Here, we introduce an intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAP() layer into hybrid heterojunction solar cells based on silicon nanowires (SINWs) and conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). The highest power conversion efficiency reaches a record 13.01%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. We show that the insertion of TAP( increases the minority carrier lifetime because of an energy offset at the heterojunction interface. Furthermore, X-ray photoemission spectroscopy reveals that TAP( can effectively block the strong oxidation reaction occurring between PEDOT:PSS and silicon, which improves the device characteristics and assurances for reliability. These learnings point toward future directions for versatile interface engineering techniques for the attainment of highly efficient hybrid photovoltaics.
A HIGHLY EFFICIENT HYBRID CDS-GAAS SOLAR CELL
(2012)
Chen, H. C.
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Lin, C. C.
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Tsai, Y. L.
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Han, H. V.
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Yu, Peichen
A novel design of hybrid solar cell combining traditional GaAs-based solar cell with colloidal CdS quantum dots (ODs) is demonstrated. By applying CdS ODs on the surface of GaAs device, we can obtain an effective antireflection coating at long wavelength. Moreover, due to its strong absorption at ultraviolet range and efficient light emission at blue photon, CdS quantum dots can down-convert the high-energy UV photons into visible ones, which are more easily to be collected in GaAs solar cell. The short circuit current and power conversion efficiency of this new device increases by 21% and 18.9%, respectively, when we compare them to the uncoated GaAs solar cell. An increase of the surface photoconductivity was also detected due to UV presence, and the fill factor of the CdS ODs solar cell can be improved accordingly.
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.
A sandwiched buffer layer enabling pulsed ultraviolet- and visible-laser annealings for direct fabricating poly-Si field-effect transistors on the polyimide
(2017-07-10)
Kao, Ming-Hsuan
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Huang, Wen-Hsien
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Shieh, Jia-Min
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Shen, Chang-Hong
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Lee, Pei-Kang
A sandwiched buffer layer of SiO2/Al/SiO2 enables ultraviolet-laser crystallization and visible-laser activation for direct fabrication of a poly-Si flexible field-effect-transistor (fFET) on polyimides. The buffer layer can produce heat accumulation and laser reflection from the Al/SiO2 interface to facilitate grain growth and contact resistance reduction of poly-Si without damaging the polyimide substrate. The feature size of poly-Si fFET has shrunk to 400nm via laser annealing, with the on/off current-ratio exceeding 5 x 10(6) and a subthreshold swing of 190 mV/dec. Moreover, the transfer characteristics of fFET by tension stress can be maintained until the bending radius reaches over 15 mm. Published by AIP Publishing.
Analysis of Strain Relaxation and Emission Spectrum of A Free-Standing GaN-based Nanopillar
(2008-01-01)
Wu, Yuh-Renn
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Yu, Peichen
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Chiu, C. H.
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Chang, Cheng-Yu
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Kuo, H. C.
We have made a, GaN-based single nanopillar with a, diameter of 300nm using the focused ion beam (FB) technique. The micro-photoluminescence (mu-PL) from the embedded GaN/InGaN multi-quantum wells reveals a blue shift of 68.3 meV in energy. In order to explain the spectrum shift, we have developed a valence force field model to study the strain relaxation mechanism in a, single GaN-based nanopillar structure. The strain distribution and strain induced polarization effect inside the multiple quantum wells is added to our self-consistent Poisson, drift-diffusion, and Schrodinger solver to study the spectrum shift of mu-PL.
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
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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.
Antireflection and Light Trapping of Periodic Subwavelength Surface Structures Formed by Colloidal Monolayer Spheres Lithography on Thin Film Solar Cells
(2010)
Tseng, P. C.
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Tsai, M. A.
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Yu, Peichen
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Kuo, H. C.
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光電工程學系
Solar cell efficiency enhancement by gradient periodic TiO(2) nanoislands formed with the facilitation of polystyrene-spheres was studied. The enhancement mechanism was categorized by antireflection and light-trapping and achieves 72% relative increase of short-circuit current density. @ 2010 Optical Society of America
Antireflection and light trapping of subwavelength surface structures formed by colloidal lithography on thin film solar cells
(2012-03-01)
Tseng, Ping-Chen
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Tsai, Min-An
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Yu, Peichen
;
Kuo, Hao-Chung
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交大名義發表
In this paper, we present a novel design of a surface nanostructure that suppresses the reflectivity and provides forward diffraction for light trapping. The structure under study comprises periodic nanoislands fabricated using self-assembly polystyrene spheres, which are applicable to large-area fabrication. We also show preliminary fabrication results of the proposed structure. The periodic nanoislands reduce the reflectivity through gradient effective refractive indices and enhance light trapping through diffraction in a periodic structure. We first systematically study the antireflection and light trapping effects using a rigorous coupled-wave analysis and then calculate the short-circuit current density of a 2-mu m-thick crystalline silicon with periodic nanoislands and an aluminum back reflector. The optimum short-circuit current density with periodic nanoislands achieves 25?mA/cm2 theoretically, which shows a 76.9% enhancement compared with that of bare silicon. Moreover, the structure also provides superior photocurrent densities at large angles of incidence, compared with conventional antireflection coatings. Copyright (c) 2011 John Wiley & Sons, Ltd.
Antireflective scheme for InGaP/InGaAs/Ge triple junction solar cells based on TiO2 biomimetic structures
(2012)
Hung, Kuo-Hsuan
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Chen, Ting-Gang
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Yang, Tung-Ting
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Yu, Peichen
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Hong, Chung-Yu
In this work, we demonstrate the device design, characterization, fabrication and analysis of biomimetic anti reflective structures on III-V multi-junction solar cell. The cell without anti reflective structure has a severe change of refractive index between the cell and air, causing a huge reflection (about 30%) and decrease the cell efficiency significantly. We can reduce light reflection by coating a proper material on the cell, diminishing the refractive index difference between cell and air interface. The optimization of single antireflection coating and biomimetic structure will be discussed and the experimental results will also be presented.
Approaching conversion limit with all-dielectric solar cell reflectors
(2015-02-09)
Fu, Sze Ming
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Lai, Yi-Chun
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Tseng, Chi Wei
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Yan, Sheng Lun
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Zhong, Yan Kai
Metallic back reflectors has been used for thin-film and wafer-based solar cells for very long time. Nonetheless, the metallic mirrors might not be the best choices for photovoltaics. In this work, we show that solar cells with all-dielectric reflectors can surpass the best-configured metal-backed devices. Theoretical and experimental results all show that superior large-angle light scattering capability can be achieved by the diffuse medium reflectors, and the solar cell J-V enhancement is higher for solar cells using all-dielectric reflectors. Specifically, the measured diffused scattering efficiency (D.S.E.) of a diffuse medium reflector is >0.8 for the light trapping spectral range (600nm-1000nm), and the measured reflectance of a diffuse medium can be as high as silver if the geometry of embedded titanium oxide(TiO2) nanoparticles is optimized. Moreover, the diffuse medium reflectors have the additional advantage of room-temperature processing, low cost, and very high throughput. We believe that using all-dielectric solar cell reflectors is a way to approach the thermodynamic conversion limit by completely excluding metallic dissipation. (C) 2015 Optical Society of America
Back-Contacted Thin-Film GaAs Solar Cells
(2016-01-01)
Hong, Chung-Yu
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Lin, Yu-Chen
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Ho, Kuan-Ying
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Tsai, Jia-Ling
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Chien, Zhan-Tien
In this work, we present a thin-film GaAs solar cell employing via contacts for forming a back-contacted solar cell to eliminate light blocking effects and enhance photon recycling at the same time. The fabrication procedure and the characterization of the fabricated devices are discussed in this paper. From our measurement, a conversion efficiency of 6.5%, open circuit voltage of 0.95 V, and a current density of 8.6mA/cm(2) under one-sun illumination were obtained in a 5x5 mm cell.
Balanced carrier transport in organic solar cells employing embedded indium-tin-oxide nanoelectrodes
(2011-02-14)
Hsu, Min-Hsiang
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Yu, Peichen
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Huang, Jen-Hsien
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Chang, Chia-Hua
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Wu, Chien-Wei
In this paper, we present evidence of balanced electron and hole transport in polymer-fullerene based solar cells by means of embedded indium-tin-oxide nanoelectrodes. Enabled by a controllable electrochemical deposition, the individual nanoelectrodes are uniformly enclosed by a poly (3,4-ethylenedioxythiophene) hole-conducting layer, allowing a relatively short route for holes to reach the anode and hence increasing the effective hole mobility. Consequently, the power conversion efficiency and photogenerated current are maximized with a deposition condition of 50 mu C, where the ratio of the electron to hole mobility is nearly unity. (C) 2011 American Institute of Physics. [doi:10.1063/1.3556565]
Balanced carrier transport in organic solar cells employing embedded indium-tin-oxide nanoelectrodes (vol 98, 073308, 2011)
(2011-03-14)
Hsu, Min-Hsiang
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Yu, Peichen
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Huang, Jen-Hsien
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Chang, Chia-Hua
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Wu, Chien-Wei
Beam Shaping of GaN/InGaN Vertical-Injection Light Emitting Diodes via High-Aspect-Ratio Nanorod Arrays
(2009)
Tsai, M. A.
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Yu, Peichen
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Chao, C. L.
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Chiu, C. H.
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Kuo, H. C.
The enhanced light extraction and collimated output beam profile from GaN/InGaN vertical-injection light emitting diodes are demonstrated utilizing high-aspect-ratio nanorod arrays. The nanorod arrays are patterned by self-assembled silica spheres, followed by inductively-coupled-plasma reactive-ion-etching. (C) 2008 Optical Society of America
Biomimetic Antireflection Coating for Efficiency Enhancement of Triple-Junction Solar Cells Utilizing Nanosphere Lithography
(2010)
Chiu, M. Y.
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Chang, F. Y.
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Chang, C. H.
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Tsai, M. A.
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Yu, Peichen
In this work, we demonstrate a thorough device design, fabrication, characterization, and analysis of biomimetic antireflective structures implemented on a Ga(0.5)In(0.5)P/GaAs/Ge triple-junction solar cell. The sub-wavelength structures are fabricated on a silicon nitride passivation layer using polystyrene nanosphere lithography followed by anisotropic etching. Both the reflectance spectroscopy and external quantum efficiency measurements confirm the improved optical absorption in the ultraviolet/blue and near-infrared wavelengths. Hence, the conversion efficiency of cell with sub-wavelength structure (SWS) is enhanced by 46.1% and 3.4% due to much improved current-matching, compare to cells without an ARC and SL ARC, respectively. We further employ RCWA method to analyze the reflectance by tuning structural factors such as periodicity or height of the SWS.
Bridging the "green gap" of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals
(2016-01-01)
Tsai, Yu-Lin
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Liu, Che-Yu
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Krishnan, Chirenjeevi
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Lin, Da-Wei
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Chu, You-Chen
Green LEDs do not show the same level of performance as their blue and red cousins, greatly hindering the solid-state lighting development, which is the so-called "green gap". In this work, nano-void photonic crystals (NVPCs) were fabricated to embed within the GaN/InGaN green LEDs by using epitaxial lateral overgrowth (ELO) and nano-sphere lithography techniques. The NVPCs act as an efficient scattering back-reflector to outcouple the guided and downward photons, which not only boost the light extraction efficiency of LEDs with an enhancement of 78% but also collimate the view angle of LEDs from 131.5 degrees to 114.0 degrees. This could be because of the highly scattering nature of NVPCs which reduce the interference giving rise to Fabry-Perot resonance. Moreover, due to the threading dislocation suppression and strain relief by the NVPCs, the internal quantum efficiency was increased by 25% and droop behavior was reduced from 37.4% to 25.9%. The enhancement of light output power can be achieved as high as 151% at a driving current of 350 mA. Giant light output enhancement and directional control via NVPCs point the way towards a promising avenue of solid-state lighting.
Broad Angular and Spectral Anti-Reflection Employing GaN Nano-Pillar Structures
(2008)
Chiu, C. H.
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Yu, Peichen
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Chen, C. C.
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Kuo, H. C.
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Lu, T. C.
Angular and spectral reflectivities of GaN nano-pillar structures are investigated for heights of 350nm, 550nm and 720 nm. Calculations based on rigorous coupled-wave analysis show excellent agreement with the measured reflectivities for s- and p-polarizations. (c) 2008 Optical Society of America