Browsing by Author "Lai, Yi-Chun"

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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.
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.
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
Characteristics of Conductive Polymer/Silicon Heterojunction Solar Cells with Periodic Nanostructures
(2013)
Huang, Yang-Yue
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Pan, Ward
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Lai, Yi-Chun
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Yang, T. T.
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Chen, Riqui
Mono- and multi-crystalline silicon photovoltaics currently still hold more than 80% market share because of the non-toxic, abundant material resources used, and their long-term stabilities. However, the cost of solar power is still more than three times that of fossil fuels, which necessitates a further reduction to accelerate its widespread use. It has been estimated that cell fabrication consumes 30% of the total manufacturing cost due to energy intensive semiconductor processes, such as high temperature furnace for doping, electrodes co-firing, high-vacuum chemical deposition, etc. Therefore, the organic-inorganic hybrid cell concept has been proposed to take advantage of the solution-based processes for rapid and low-cost production and the wide absorption spectrum of silicon. In this work, we demonstrate a hybrid heterojunction solar cell based on the structure of conductive polymer PEDOT:PSS spun cast on n-type crystalline silicon nanorod (SiNR) arrays with periodic arrangements. The nanorod arrays are fabricated by electron beam (E-beam) lithography followed by reactive-ion etching (RIE), which show capability to enhance light harvesting. In addition, SiNRs and PEDOT:PSS can form core-shell structure that provides a large p-n junction area for carrier separation and collection. We measured the optical and photovoltaic characteristics of these devices under a simulated class A solar simulator with a calibrated illumination intensity of 1000 W/m(2) for the AM1.5G solar spectrum. A post-RIE damage removal etching (DRE) is subsequently introduced in order to mitigate the surface recombination issues and also alter the surface reflection due to modifications in the nanorod side-wall profile. Finally, we show that the DRE treatment can effectively recover the carrier lifetime and dark current-voltage characteristics of SiNRs hybrid solar cells to resemble the planar counterpart without RIE damages.
Chemical vapor deposition growth of bilayer graphene via altering gas flux geometry
(2019-11-30)
Petrov, Stefan
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Rafailov, Peter M.
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Marinova, Vera
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Lin, Shiuan-Huei
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Lai, Yi-Chun
Graphene films with high content of bilayer graphene are obtained by chemical vapor deposition technique on copper (Cu) foil by means of suitably designing the flux geometries of the reactant gases. First single-layer graphene growth is optimized using a preliminary oxygen passivation of the Cu substrate which facilitates the formation of larger graphene grains with low defect density. Then, in order to enhance the transport of reactant species to the catalyst substrate, the gas flux geometry is modified in two ways: (i) fixing a graphite holder next to the Cu substrate perpendicular to the stream of the flux gases or (ii) positioning the Cu foil into a graphite shelter. It is found that both modifications facilitate the growth of a second graphene layer leading to increased formation of bilayer graphene. The obtained graphene layers are characterized by Raman spectroscopy (with special focus on the overtone (2D) of the disorder-induced band), scanning electron microscopy, transmission electron microscopy, atomic force microscope analysis and optical transmission measurements. Narrow symmetric 2D Raman peaks with linewidths ranging down to 22 cm(-1) but blue-shifted with respect to that of single-layer graphene are obtained from graphite holder- and shelter-grown samples indicating high-quality bilayer graphene.
Conductive Polymer/GaAs Hybrid Heterojunction Photovoltaic Devices
(2013)
Pan, Huai-Te
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Huang, Yang-Yue
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Weng, Wei-Sheng
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Chen, Po-Han
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Cheng, Kai-Yuan
Hybrid solar cells combining organic polymers and inorganic semiconductors are extensively investigated recently due to relatively inexpensive cost and simple fabrication processes. In this work, we demonstrate organic/inorganic hybrid heterojunction solar cells based on gallium arsenide (GaAs) substrate and conjugated polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). First we performed a one-dimensional device simulation based on a self-consistent Poisson and drift-diffusion solver to survey the band alignment between the conductive polymer and GaAs materials and achieve a practical device design. Second, for device fabrication, we prepare a cleaned one-side-polished planar GaAs wafer, followed by thermal evaporation of back-side metal using either Aluminum or titanium/gold as the cathode. Next, PEDOT:PSS is spun-cast onto the wafer and annealed at 115 degrees C for 10 minutes. To improve carrier conduction, we use a self-assembled polystyrene (PS) nanosphere lithography technique to form the sacrificial mask layer, and perform anisotropic metal-assisted chemical etching on GaAs substrates. Various nanostructures such as nanowires or nanorods allow the conformal p-n heterojunction formation at the interface of organic/inorganic semiconductors, which can be beneficial for both light absorption and carrier collection. The optical and electrical characteristics such as reflectance, current voltage, and external quantum efficiency are measured. Currently, we achieve a 3.2% power conversion efficiency with an open-circuit voltage of 0.565 V, short-circuit current of 8.95 mA/cm(2), and a fill factor of 63.29% under a simulated AM1.5G illumination for planar substrates. Device fabrication with GaAs nanowires is still in process and more data will be presented.
Doping of Monolayer Graphene for Silicon based Schottky Junction Solar Cells
(2013)
Lai, Yi-Chun
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Wu, Bing-Shu
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Yu, Shu-Cheng
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Yu, Peichen
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Chi, Gou-Chung
Silicon-based hybrid solar cells have garnered extensive attentions in the photovoltaics industry due to easy processing attributes and high optical absorption and outstanding carrier mobility of silicon. Among all, indium tin oxide (ITO)/silicon solar cells have achieved a power conversion efficiency of 13% due to excellent conductivity, transmittance and applicable surface potential of ITO. However, the cost of ITO has risen significantly recently due to the deficiency of indium. Therefore, graphene has been an inexpensive alternative to ITO. For solar cell applications, graphene plays an important role as transparent electrodes (TE) with tunable work functions for efficient carrier collection. Therefore, graphene-based Schottky junction solar cells (SJSC) on crystalline silicon thin films hold great promises for low-cost photovoltaics owing to potentials for high efficiency and rapid production on flexible substrates. According to previous reports, the key factors to achieve a highly efficient SJSC include excellent transparence and conductance, as well as tunable work functions. Herein, we demonstrate a single layer graphene/n-Si Schottky junction solar cell that exhibits a power conversion efficiency (PCE) of 1.2 % under one-sun AM 1.5G illumination, and an integrated short-circuit photocurrent of 18.3 mA/cm(2) from the external quantum efficiency measurement. The transmittance of the monolayer graphene in this device is over 97 % and the sheet resistance is around 800 to 1200 Omega/square. Furthermore, we investigate a doping method involving bis(trifluoromethanesulfonyl)-amid (TFSA) for the monolayer graphene to improve the separation and collection of photogenerated carriers in the SJSC. The preliminary data show that the sheet resistance is decreased rapidly from 1200 to 300 Omega/square. and the surface potential is also adjusted by the chemical doping. Currently, device fabrication with doped monolayer graphene is still in process and complete characterization data will be presented.
Efficiency Enhancement of Organic/GaAs Hybrid Photovoltaic Cells Using Transparent Graphene as Front Electrode
(2016-03)
Huang, Chi-Hsien
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Yu, Shu-Chen
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Lai, Yi-Chun
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Chi, Gou-Chung
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Yu, Peichen
Large-area graphene of high quality and uniformity was successfully grown by chemical vapor deposition (CVD) using surface oxidation treatment of copper foil prior to the graphene growth step. The graphene was transferred to the polyethylene terephthalate (PET) substrate (G/PET) to act as a transparent front electrode of hybrid heterojunction photovoltaic (PV) cells; these cells were based on a structural motif of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the p-type semiconductor, GaAs (1 0 0) as the inorganic n-type semiconductor, and a silver comb electrode atop of PEDOT: PSS. By using G/PET as a transparent front electrode, the power conversion efficiency (PCE), under simulated AM1.5G illumination conditions, was greatly enhanced by up to 26% (from 6.85% to 8.60%). All PV characteristics, including open-circuit voltage (V-oc), short-circuit current (J(sc)), and fill factor (FF), contributed to this PCE enhancement. The reflectance, external quantum efficiency, and dark current were investigated to explain this observed PCE enhancement. Although two layers of graphene can efficiently reduce the sheet resistance, the reduction of transmittance in multilayer cells resulted in lower short-circuit current density, leading to lower PCE, in comparison with those with only one layer of graphene.
Efficient hybrid white light-emitting diodes by organic-inorganic materials at different CCT from 3000K to 9000K
(2015-04-06)
Chen, Kuo-Ju
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Lai, Yi-Chun
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Lin, Bin-Cheng
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Lin, Chien-Chung
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Chiu, Sheng-Huan
The hybrid white light-emitting didoes (LED) with polyfluoren (PFO) polymer and quantum dot (QD) was investigated using dispensing method at the different correlated color temperature (CCT) for cool and warm color temperature. This result indicates that the hybrid white LED device has the higher luminous efficiency than the convention one, which could be attributed to the increased utilization rate of the UV light. Furthermore, the CIE 1931 coordinate of high quality white hybrid LED with different CCT range from 3000K to 9000K is demonstrated. Consequently, the angular-dependent CCT and the thermal issue of the hybrid white LED device were also analyzed in this study. (C) 2015 Optical Society of America
Fabrication of Flexible White Light-Emitting Diodes from Photoluminescent Polymer Materials with Excellent Color Quality
(2017-10-11)
Lin, Huang-Yu
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Sher, Chin-Wei
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Lin, Chih-Hao
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Tu, Hsien-Hao
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Chen, Xin Yin
This study developed flexible light-emitting diodes (LEDs) with warm white and neutral white light. A simple ultraviolet flip-chip sticking process was adopted for the pumping source and combined with polymer and quantum dot (QD) films technology to yield white light. The polymer-blended flexible LEDs exhibited higher luminous efficiency than the QD-blended flexible LEDs. Moreover, the polymer-blended LEDs, achieved excellent color-rendering index (CRI) values (Ra = 96 and R9 = 96), with high reliability, demonstrating high suitability for special applications like accent, down, or retrofit lights in the future. In places such as a museum, kitchen, or surgery room, its high R9 and high CRI characteristics can provide high-quality services.
Fabrication of InGaN/GaN Nanodisk Structure by using Bio-template and Neutral Beam Etching Process
(2015)
Lai, Yi-Chun
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Higo, Akio
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Lee, Chang Yong
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Thomas, Cedric
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Tanikawa, Tomoyuki
Quantum dot optoelectronic devices are very attractive for their low power consumption, temperature stability, and high-speed modulation. We developed a defect-less, top-down fabrication process for sub-12-nm diameter InGaN quantum nanodisks (NDs) embedded in GaN barrier by using a combination of a bio-template and neutral beam etching. We have achieved high density of 2.6 x 10(11) cm(-2) with 6-nm in diameter and 15-nm-high nanopillars.
GaN-based light-emitting diodes with graphene/indium tin oxide transparent layer
(2014-03-10)
Lai, Wei-Chih
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Lin, Chih-Nan
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Lai, Yi-Chun
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Yu, Peichen
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Chi, Gou Chung
We have demonstrated a gallium nitride (GaN)-based green light-emitting diode (LED) with graphene/indium tin oxide (ITO) transparent contact. The ohmic characteristic of the p-GaN and graphene/ITO contact could be preformed by annealing at 500 degrees C for 5 min. The specific contact resistance of p-GaN/graphene/ITO (3.72E-3 Omega(center dot)cm(2)) is one order less than that of p-GaN/ITO. In addition, the 20-mA forward voltage of LEDs with graphene/ITO transparent (3.05 V) is 0.09 V lower than that of ITO LEDs (3.14 V). Besides, We have got an output power enhancement of 11% on LEDs with graphene/ITO transparent contact. (C)2014 Optical Society of America
Gas permeable silver nanowire electrode for realizing vertical type sensitive gas sensor
(2014-11-01)
Chuang, Ming-Yen
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Zan, Hsiao-Wen
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Yu, Peichen
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Lai, Yi-Chun
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Meng, Hsin-Fei
We successfully demonstrated a Poly (3-hexylthiophene) (P3HT) diode gas sensor with silver nanowires as a gas permeable top electrode. The silver nanowires dispersed in isopropyl alcohol (IPA) were used to form a top electrode by a simple drop-casting method. The meshes between nanowires enable gas molecules pass through the electrode and diffuse into the underlying organic sensing layer to dope or dedope the organic semiconductor. Here, the proposed sensor successfully detects ammonia down to 30 parts-per-billion (ppb), which is sensitive enough in many applications including breath ammonia monitoring as a point-of-care application. (C) 2014 Elsevier B.V. All rights reserved.
High-efficiency polymer solar cells by blade coating in chlorine-free solvents
(2014-04-01)
Tsai, Pei-Ting
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Tsai, Chia-Ying
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Wang, Chun-Ming
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Chang, Yu-Fan
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Meng, Hsin-Fei
High-performance polymer cells are typically fabricated by employing toxic solvents such as dichlorobenzene and chlorobenzene. In this study, blade coating with the chlorine-free solvents toluene and xylene is applied to polymer solar cells that contained the low band-gap polymer PBDTTT-C-T blended with [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM). The highest efficiencies of the cells fabricated in toluene and xylene solutions were 6.09% and 6.11%, respectively. Atomic force microscopy images show that the films formed by blade coating using toluene and xylene were extremely smooth, with roughness of only 1 nm. This blade coating has a rapid-drying in a few seconds without the long-running thermal or solvent annealing. The possibility of high-volume environmentally-friendly fabrication of efficient polymer solar cells with minimal material waste is thus demonstrated using a combination of chlorine-free solvents and blade coating. (C) 2014 Elsevier B.V. All rights reserved.
Highly Effective Field-Effect Mobility Amorphous InGaZnO TFT Mediated by Directional Silver Nanowire Arrays
(2015-01-14)
Liu, Hung-Chuan
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Lai, Yi-Chun
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Lai, Chih-Chung
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Wu, Bing-Shu
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Zan, Hsiao-Wen
In this work, we demonstrate sputtered amorphous indium-gallium-zinc oxide thin-film transistors (a-IGZO TFTs) with a record high effective field-effect mobility of 174 cm(2)/V s by incorporating silver nanowire (AgNW) arrays to channel electron transport. Compared to the reference counterpart without nanowires, the over 5-fold enhancement in the effective field-effect mobility exhibits clear dependence on the orientation as well as the surface coverage ratio of silver nanowires. Detailed material and device analyses reveal that during the room-temperature IGZO sputtering indium and oxygen diffuse into the nanowire matrix while the nanowire morphology and good contact between IGZO and nanowires are maintained. The unchanged morphology and good interfacial contact lead to high mobility and air-ambient-stable characteristics up to 3 months. Neither hysteresis nor degraded bias stress reliability is observed. The proposed AgNW-mediated a-IGZO TFTs are promising for development of large-scale, flexible, transparent electronics.
Hybrid Carbon Nanotube/Silicon Schottky Junction Solar Cells
(2016-01-01)
Chen, Sih-Han
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Lai, Yi-Chun
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Tsai, Pei-Ting
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Lin, Yi-Cheng
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Lin, Yan-Nan
In this work, highly transparent and conductive multi-wall-carbon nanotubes (MW-CNTs) are employed to realize solution-processed, hybrid silicon (Si) Schottky -junction solar cells. We first describe the optimization of device structures on silicon wafers with nanowire and micro-pyramidal surface textures, and compare the device characteristics with those of hybrid cells based on Si and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS). The optimized processing conditions include the length of silicon nanowires, the annealing temperature, and the shading ratio of the frontal silver grids. It is found that the hybrid CNT cells outperform the hybrid PEDOT: PSS counterpart under individually optimized processing conditions due to better transparency and conductivity of CNTs than PEDOT: PSS. The best hybrid CNT cells, fabricated using a 14% grid shield ratio, 150 degrees C annealing temperature, and 150nm nanowire length, achieve a PCE of 11.90% and 13.82% in micro-pyramid and nanowire (NW) textured silicon, respectively, in contrast to 7.43% and 12.96% for hybrid PEDOT: PSS cells. To control the rear surface recombination, we further employ two solution-processed, small-molecule materials, Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol- 5-yl) benzene (OXD-7) via a blade-coating technique between the silicon wafer and aluminum electrode. As a result, the PCE of hybrid CNT/Si NW solar cells is enhanced to 13.92% and 14.41% with the insertion of the Alq3 and OXD-7 rear interlayer, respectively. With the high power conversion efficiency (PCE), manufacturing Si-based solar cells at temperatures below 150 degrees C without high vacuum conditions not only significantly lowers the fabrication cost, but also enables the use of ultrathin substrates to save on the material cost for the future.
Hybrid Multi-Layer Graphene/Si Schottky Junction Solar Cells
(2013)
Wu, Bing-Shu
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Lai, Yi-Chun
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Cheng, Yuan-Hung
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Yu, Shu-Cheng
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Yu, Peichen
Hybrid Graphene/Si Schottky junction solar cells are inexpensive alternatives for photovoltaics due to easy and rapid fabrication processes. However, one of the main challenges for graphene-based Schottky junction solar cells is the large sheet resistance of single-layer graphene, leading to low fill factor. Here, we demonstrate multi-layer graphene-based Schottky junction solar cell, which are prepared by stacking monolayer graphene via a chemical vapor deposition (CVD) method on copper foils. The objectives are to improve charge transport and decrease the series resistance of the hybrid solar cell. We present the Raman spectrum results of monolayer graphene and stacked multilayer graphene films, and observe no bonding interaction between the stacked layers. For the optical and electrical properties, the sheet resistance of stacked multilayer graphene is reduced from 3000 Omega/sq to 1500 Omega/sq and 750 Omega/sq with two and three layers, respectively. The reduction of the sheet resistance approaches the properties of highly-oriented pyrolytic graphite (HOPG) when the layer number is more than five. Moreover, from the optical transmittance measurement, the absorption of a monolayer graphene is about 3% at the 555 nm wavelength, giving rise to a transmittance of 90% for triple-layer graphene. The hybrid silicon solar cell with a single-layer graphene achieves a power conversion efficiency of 0.9% with a short-circuit current of 8.75 mA/cm(2), open-circuit voltage of 0.25V, and fill factor of 39% The external quantum efficiency measurement reveals an integrated photocurrent of 18.3 mA/cm(2), which further confirms the potential of the hybrid photovoltaic approach. Device fabrication with multi-layer graphene is still in process, and more data will be presented. Other characterization techniques such as capacitance-voltage and capacitance-frequency measurements will be taken to analyze the performance of the single- and multi-layer graphene solar cells.
Impact of Light Management on Photovoltaic Characteristics of GaAs Solar Cells with Photonic Crystals and Quasi-Photonic Crystals
(2014)
Lai, Yi-Chun
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Yang, Tung-Ting
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Yu, Peichen
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Hung, Mu-Min
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Charlton, Martin
In detailed balance model, the efficiency of single-junction solar cells can be potentially as high as 33.5% under AM 1.5G illumination. However the best state-of-the-art devices are still far lower than those figures, even the electronic quality is nearly perfect. Therefore the efficiency gap should stem from the light management inside solar cells. Recently, external radiation efficiency (eta ext) derived from detailed balance model is emphasized to evaluate light management and photon recycling, which aggregates the loss of backward emission into substrate and non-radiative recombination. This factor can be highly relevant to the cell\'s performance, especially open-circuit voltage (Voc), and maximizing Voc is generally considered as the last mile to approach ultra-high efficiency limit. In this work, we try to quantify the Voc enhancement in GaAs solar cells by enhancing light extraction. The simulation tools are RCWA simulation and photon recycling model NREL developed recently. The top structures we simulate here are TiO2 cones arranged in three PC/QPC lattices. After our calculation, the QPC 12-folds symmetry can make the biggest Voc enhancement 11.21meV compared with bare one, and the structure also possess extraordinary omni-directional anti-reflection ability for maintaining high Jsc. Our results also show that using this way to enhance Voc is especially suitable for cells with ordinary material quality. Therefore, the requests of ideal top structures for solar cells\' use are not only near-perfect anti-reflection, but the ability to maximize light extraction if no feature of angular filter exists.
Nanometer scale fabrication and optical response of InGaN/GaN quantum disks
(2016-10-21)
Lai, Yi-Chun
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Higo, Akio
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Kiba, Takayuki
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Thomas, Cedric
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Chen, Shula
In this work, we demonstrate homogeneously distributed In0.3Ga0.7N/GaN quantum disks (QDs), with an average diameter below 10 nm and a high density of 2.1 x 10(11) cm(-2), embedded in 20 nm tall nanopillars. The scalable top-down fabrication process involves the use of self-assembled ferritin bio-templates as the etch mask, spin coated on top of a strained In0.3Ga0.7N/GaN single quantum well (SQW) structure, followed by a neutral beam etch (NBE) method. The small dimensions of the iron cores inside ferritin and nearly damage-free process enabled by the NBE jointly contribute to the observation of photoluminescence (PL) from strain-relaxed In0.3Ga0.7N/GaN QDs at 6 K. The large blueshift of the peak wavelength by over 70 nm manifests a strong reduction of the quantum-confined Stark effect (QCSE) within the QD structure, which also agrees well with the theoretical prediction using a 3D Schrodinger equation solver. The current results hence pave the way towards the realization of large-scale III-N quantum structures using the combination of bio-templates and NBE, which is vital for the development of next-generation lighting and communication devices.
Non-reciprocal meta-surfaces for nanophtonic light trapping: optical isolators versus solar cells
(2015)
Fu, Sze Ming
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Zhong, Yan Kai
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Yan, Sheng Lun
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Ju, Nyan Ping
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Chen, Po Yu
Nano-photonic concept has been shown to be very effective for boosting solar cell conversion efficiency. In this work, the novel concepts of non-reciprocality and chiral meta-surface are demonstrated to be very useful for photovoltaics. The asymmetric chiral patterns are designed and optimized using genetic algorithm. The enhanced optical absorption is observed and it is attributed to the non-reciprocal nature of the solar cell front meta-surface. The asymmetric solar cell front surface enhances the anti-reflection and, at the same time, forbids the photon escape once it enters the devices. This concept is very similar to optical isolators where one-way transmission is intentionally designed for enhanced optical diode effect. Preliminary experimental results are supplied to confirm the superiority of asymmetric chiral design. The ongoing experimental effort is adjusting the PECVD deposition conditions to boost the efficiency on patterned substrates.