Browsing by Author "Pao, Chun-Wei"

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2-Alkyl-5-thienyl-Substituted Benzo[1,2-b:4,5-b ']dithiophene-Based Donor Molecules for Solution-Processed Organic Solar Cells
(2013-10-09)
Patra, Dhananjaya
;
Huang, Tzu-Yen
;
Chiang, Chao-Cheng
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Maturana, Ramon Orlando Valencia
;
Pao, Chun-Wei
In this study, we have strategically designed and convergently synthesized two novel, symmetrical, and linear A-D-A-type pi-conjugated donor molecules (TBDTCNR, TBDTCN), each containing a planar electron-rich 2-octylthiene-5-yl-substituted benzodithiophene (TBDT) unit as the core, flanked by octylthiophene units and end-capped with electron-deficient cyanoacetate (CNR) or dicyanovinyl (CN) units. We thoroughly characterized both of these materials and investigated the effects of the end groups (CNR, CN) on their optical, electrochemical, morphological, and photovoltaic properties. We then fabricated solution-processed bulk heterojunction organic solar cells incorporating TBDTCNR and TBDTCN. Among our tested devices, the one containing TBDTCNR and [6,6]-phenyl-C-61-butyric acid methyl ester in a 1:0.40 ratio (w/w) exhibited the highest power conversion efficiency (5.42%) with a short-circuit current density (J(sc)) of 9.08 mA cm(-2), an open circuit voltage (V-oc) of 0.90 V, and an impressive fill factor (FF) of 0.66 under AM 1.5G irradiation (100 mW cm(-2)). The FFs of these solution-processed small-molecule organic solar cells (SMOSCs) are outstanding when compared with those recently reported for benzodithiophene (BDT)-based SMOSCs, because of the high crystallinity and excellent stacking properties of the TBDT-based compounds.
Low-temperature grown graphene films by using molecular beam epitaxy
(2012-11-26)
Lin, Meng-Yu
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Guo, Wei-Ching
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Wu, Meng-Hsun
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Wang, Pro-Yao
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Liu, Te-Huan
Complete graphene film is prepared by depositing carbon atoms directly on Cu foils in a molecular beam epitaxy chamber at 300 degrees C. The Raman spectrum of the film has indicated that high-quality few-layer graphene is obtained. With back-gated transistor architecture, the characteristic current modulation of graphene transistors is observed. Following the similar growth procedure, graphitization is observed at room temperature, which is consistent with the molecular dynamics simulations of graphene growth. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768948]
Mitigating Metal Dendrite Formation in Lithium-Sulfur Batteries via Morphology-Tunable Graphene Oxide Interfaces
(2019-01-16)
Chen, Yu-Ting
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Abbas, Syed Ali
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Kaisar, Nahid
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Wu, Sheng Hui
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Chen, Hsin-An
Despite issues related to dendrite formation, research on Li metal anodes has resurged because of their high energy density. In this study, graphene oxide (GO) layers are decorated onto Li metal anodes through a simple process of drop-casting and spray-coating. The self-assembly of GO is exploited to synthesize coatings having compact, mesoporous, and macroporous morphologies. The abilities of the GO coatings to suppress dendrite formation are compared through Li vertical bar Li symmetrical cell charging at a current density of 5 mA cm(-2) for 2000 cycles-a particularly abusive test. The macroporous structure possesses the lowest impedance, whereas the compact structure excels in terms of stability. Moreover, GO exhibits a low nucleation overpotential and is transformed into reduced GO with enhanced conductivity during the operation of the cells; both factors synergistically mitigate the issue of dendrite formation. Li-S batteries incorporating the GO-decorated Li anodes exhibit an initial capacity of 850 mA h g(-1) and maintain their stability for 800 cycles at a C-rate of 1 C (1675 mA h g(-1)), suggesting the applicability of GO in future rechargeable batteries.
Single-Crystal Antimonene Films Prepared by Molecular Beam Epitaxy: Selective Growth and Contact Resistance Reduction of the 2D Material Heterostructure
(2018-05-02)
Chen, Hsuan-An
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Sun, Hsu
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Wu, Chong-Rong
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Wang, Yu-Xuan
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Lee, Po-Hsiang
Single-crystal antimonene flakes are observed on sapphire substrates after the postgrowth annealing procedure of amorphous antimony (Sb) droplets prepared by using molecular beam epitaxy at room temperature. The large wetting angles of the antimonene flakes to the sapphire substrate suggest that an alternate substrate should be adopted to obtain a continuous antimonene film. By using a bilayer MoS2/sapphire sample as the new substrate, a continuous and single-crystal antimonene film is obtained at a low growth temperature of 200 degrees C. The results are consistent with the theoretical prediction of the lower interface energy between antimonene and MoS2. The different interface energies of antimonene between sapphire and MoS2 surfaces lead to the selective growth of antimonene only atop MoS2 surfaces on a prepatterned MoS2/sapphire substrate. With similar sheet resistance to graphene, it is possible to use antimonene as the contact metal of 2D material devices. Compared with Au/Ti electrodes, a specific contact resistance reduction up to 3 orders of magnitude is observed by using the multilayer antimonene as the contact metal to MoS2. The lower contact resistance, the lower growth temperature, and the preferential growth to other 2D materials have made antimonene a promising candidate as the contact metal for 2D material devices.
The formation mechanisms and optical characteristics of GaSb quantum rings
(2013-08-07)
Lin, Wei-Hsun
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Wang, Kai-Wei
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Liao, Yu-An
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Pao, Chun-Wei
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Lin, Shih-Yen
The growth mechanisms and optical characteristics of GaSb quantum rings (QRs) are investigated. Although As-for-Sb exchange is the mechanism responsible for the dot-to-ring transition, significant height difference between GaSb quantum dots (QDs) and QRs in a dot/ring mixture sample suggests that the dot-to-ring transition is not a spontaneous procedure. Instead, it is a rapid transition procedure as long as it initiates. A model is established to explain this phenomenon. Larger ring inner diameters and heights of the sample with longer post Sb soaking time suggest that As-for-Sb exchange takes places in both vertical and lateral directions. The decreasing ring densities, enlarged ring inner/outer diameters and eventually flat GaSb surfaces observed with increasing growth temperatures are resulted from enhanced adatom migration and As-for-Sb exchange with increasing growth temperatures. (C) 2013 AIP Publishing LLC.
Thermoelectric Efficiency of Single-Molecule Junctions: Phase Diagram Constructed from First-Principles Calculations
(2015-12-31)
Amanatidis, Ilias
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Kao, Jing-Yao
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Du, Li-Yang
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Pao, Chun-Wei
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Chen, Yu-Chang
To understand the behavior of thermoelectric efficiency of single-molecule junctions from 0 K to room temperature, we investigated the thermoelectric properties of a dibenzenedithiol (DBDT) single-molecule junction. We investigated its Seebeck coefficient (S), electric conductance (sigma), and electron\'s thermal conductance (kappa(el)) in the framework of Ai/parameter-free density functional theory combined with the Lippmann Schwinger formalism in scattering approach. We observe that the nanojunction is p-type and the value of the Seebeck coefficient at room temperature is around 40 mu V/A, in agreement with the results of the experiment. In addition, we investigate the phonon\'s thermal conductance (kappa(ph)) using (i) the weak-link model suitable for ballistic phonon transport mechanism in the low-temperature quantum regime and (ii) the nonequilibrium molecular dynamics (NEMD) simulation in the high-temperature classical regime. We finally construct the phase diagram for ZT, where the value of ZT reveals the power law behavior that falls into four phases because of the competition between kappa(el) and kappa(ph) and the crossover from the quantum to classical phonon transport mechanism for kappa(ph). Our theory shows the following ZT proportional to T-alpha where x = 2, 0, 2.26, and 3 in different temperature regimes labeled by I, II, III, and IV, respectively.
Transferring-free and large-area graphitic carbon film growth by using molecular beam epitaxy at low growth temperature
(2015-09-01)
Lin, Meng-Yu
;
Wang, Cheng-Hung
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Pao, Chun-Wei
;
Lin, Shih-Yen
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顯示科技研究所
Graphitic carbon films prepared by using molecular beam epitaxy (MBE) on metal templates with different thicknesses deposited on SiO2/Si substrates are investigated in this paper. With thick Cu templates, only graphitic carbon flakes are obtained near the Cu grain boundaries at low growth temperatures on metal/SiO2 interfaces. By replacing the Cu templates with thin Ni templates, complete graphitic carbon films with superior crystalline quality is obtained at 600 degrees C on SiO2/Si substrates after removing the Ni templates. The enhanced attachment of the graphitic carbon film to the SiO2/Si substrates with reduced Ni thickness makes the approach a promising approach for transferring-free graphene preparation at low temperature by using MBE. (C) 2015 Elsevier B.V. All rights reserved.