Browsing by Author "Huang, Chi-Hsien"

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Efficiency Enhancement of Organic/GaAs Hybrid Photovoltaic Cells Using Transparent Graphene as Front Electrode
(2016-03)
Huang, Chi-Hsien
;
Yu, Shu-Chen
;
Lai, Yi-Chun
;
Chi, Gou-Chung
;
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.
Fabrication of two-dimensional photonic crystals of tethered polyvinyltetrazole on silicon surfaces for visualization in Cu2+ ion sensing
(2017-04)
Zeng, Jun-Ru
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Cheng, Chih-Chia
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Chang, Chi-Jung
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Huang, Chi-Hsien
;
Chen, Jem-Kun
We grafted polyacrylonitrile (PAN) from a flat silicon substrate via atom transfer radical polymerization (ATRP) as a bottom layer. Fabrication processes, involving very-large-scale integration (VLSI) and reactive ion etching (RIE), are sequentially used to generate 800 nm-diameter hole array of tethered PAN layer as two-dimensional photonic crystals (2DPCs). The tethered PAN 2DPCs were then subjected to a cyano-totetrazole conversion reaction to generate tethered polyvinyltetrazole (PVT) 2DPCs. Fabricating hole array could be regarded as air filling within the PVT layer, resulted in a significant decrease of effective refractive index of the PVT film. In addition, the adsorption of Cu2+ ions to the tetrazolyl groups was highly selective in solutions also containing Na+, K+, Ca2+, and Mg2+ ions. After absorption of Na+, K+, Ca2+, Mg2+, Fe3+, and Zn2+ ions, the tethered PVT 2DPC displayed insignificant changes in its effective refractive index; in contrast, upon absorbing Cu2+ ions, a dramatic change in effective refractive index occurred, resulting in a color change from red to green, observable to the naked eye along an incident angle of 30-40 degrees. The holes dimension within the array of tethered PVT shrunk after absorption of Cu2+ ions leading to a predominated blue-shift in the diffractive peak position. The tethered PVT 2DPC-based assay exhibited high sensitivity and selectivity in an experimentally simple setup for visualization in Cu2+ ion sensing.(C) 2016 Elsevier Ltd. All rights reserved.
Hybrid Carbon Nanotube/Silicon Schottky Junction Solar Cells
(2016-01-01)
Chen, Sih-Han
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Lai, Yi-Chun
;
Tsai, Pei-Ting
;
Lin, Yi-Cheng
;
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.
Hydrogen plasma-treated MoSe2 nanosheets enhance the efficiency and stability of organic photovoltaics
(2019-10-07)
Wang, Hao-Cheng
;
Lin, Yu-Che
;
Chen, Chung-Hao
;
Huang, Chi-Hsien
;
Chang, Bin
In this paper we report the effect on the power conversion efficiency (PCE) and stability of photovoltaic devices after incorporating hydrogenated two-dimensional (2D) MoSe2 nanosheets into the active layer of bulk heterojunction (BHJ) organic photovoltaics (OPV). The surface properties of 2D MoSe2 nanosheets largely affect their dispersion in the active layer blend and, thus, influence the carrier mobility, PCE, and stability of corresponding devices. We treated MoSe2 nanosheets with hydrogen plasma and investigated their influence on the polymer packing and fullerene domain size of the active layer. For the optimized devices incorporating 37.5 wt% of untreated MoSe2, we obtained a champion PCE of 9.82%, compared with the champion reference PCE of approximately 9%. After incorporating the hydrogen plasma-treated MoSe2 nanosheets, we achieved a champion PCE of 10.44%-a relative increase of 16% over that of the reference device prepared without MoSe2 nanosheets. This PCE is the one of the highest ever reported for OPVs incorporating 2D materials. We attribute this large enhancement to the enhanced exciton generation and dissociation at the MoSe2-fullerene interface and, consequently, the balanced charge carrier mobility. The device incorporating the MoSe2 nanosheets maintained 70% of its initial PCE after heat-treatment at 100 degrees C for 1 h; in contrast, the PCE of the reference device decreased to 60% of its initial value-a relative increase in stability of 17% after incorporating these nanosheets. We also incorporated MoSe2 nanosheets (both with and without treatment) into a polymer donor (PBDTTBO)/small molecule (IT-4F) acceptor system. The champion PCEs reached 7.85 and 8.13% for the devices incorporating the MoSe2 nanosheets with and without plasma treatment, respectively-relative increases of 8 and 12%, respectively, over that of the reference. These results should encourage a push toward the implementation of transition metal dichalcogenides to enhance the performances of BHJ OPVs.
Surface Micro-/Nanotextured Hybrid PEDOT:PSS-Silicon Photovoltaic Cells Employing Kirigami Graphene
(2019-08-21)
Huang, Chi-Hsien
;
Chen, Zih-Yang
;
Chiu, Chi-Ling
;
Huang, Tzu-Ting
;
Meng, Hsin-Fei
Kirigami graphene allows a two-dimensional material to transform into a three-dimensional structure, which constitutes an effective transparent electrode candidate for photovoltaic (PV) cells having a surface texture. The surface texture of an inverted pyramid was fabricated on a Si substrate using photolithography and wet etching, followed by metal-assisted chemical etching to obtain silicon nanowires on the surface of the inverted pyramid. Kirigami graphene with a cross-pattern array was prepared using photolithography and plasma etching on a copper foil. Then, kirigami graphene was transferred onto hybrid heterojunction PV cells with a poly(ethylene terephthalate)/silicone film. These cells consisted of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)-(PEDOT:PSS) as the p-type semiconductor, Si(100) as the inorganic n-type semiconductor, and a silver comb electrode on top of PEDOT:PSS. The conductivity of PEDOT:PSS was greatly improved. This improvement was significantly higher than that achieved by the continuous graphene sheet without a pattern. Transmission electron microscopy and Raman spectroscopy results revealed that the greater improvement with kirigami graphene was due to the larger contact area between PEDOT:PSS and graphene. By using two-layer graphene having a kirigami pattern, the power conversion efficiency, under simulated AM1.5G illumination conditions, was significantly augmented by up to 9.8% (from 10.03 to 11.01%).