Browsing by Author "Cheng, Hao-Wen"

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Cathodic plasma-induced syntheses of graphene nanosheet/MnO2/WO3 architectures and their use in supercapacitors
(2020-05-10)
Huang, Shih-Yu
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Phuoc-Anh Le
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Yen, Po-Jen
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Lu, Yi-Chun
;
Sahoo, Sumanta Kumar
In this study, we synthesized new 0.01-2 mu m graphene nanosheet/MnO2WO3(G/MnO2/WO3) architectures through an electrochemically induced cathodic plasma process in a single batch at a lower temperature (70 degrees C) and for a shorter time (2 h) than those required for the syntheses of similar structures when using a hydrothermal method. We first obtained 0.01-1 mu m leaf-like graphene (G) nanosheets, then 0.1-0.3 mu m long and approximately 10 nm diameter petiole-like MnO2 nanowires on the G nanosheets, and finally 0.20-2.0 mu m petal-like WO3 on MnO2/G - thereby forming the G/MnO2/WO3 architectures - as evidenced using scanning electron microscopy and transmission electron microscopy. We deciphered the step-wise reaction mechanism behind the formation of the G/MnO2/WO3 architectures during the plasma process. The high surface area of 291 m(2) g(-1) in the G/MnO2/WO3 architecture was contributed mainly by the G nanosheets, providing a suitable surface area for diffusion of the charge carriers during the charging and discharging process. As a result, an electrode incorporating the G/MnO2/WO3 architectures exhibited an excellent specific capacitance of 620 F g(-1) - 45 and 200% higher than those of G/MnO2 (421 F g(-1)) and G (189 F g(-1)) electrodes, respectively - at a current density of 0.5 A g(-1). Moreover, the G/MnO2/WO3-incorporated electrode exhibited good electrochemical cycling stability, with 90% capacitance retention over 5000 cycles at 1 A g(-1). Such new G/MnO2/WO3 heterojunction structures, not only provide high-performance electrode applications, but also suggest a potential approach toward fabricating other heterojunction structures having high surface areas for energy storage applications. (C) 2020 Elsevier Ltd. All rights reserved.
Efficient Tandem Organic Photovoltaics with Tunable Rear Sub-cells
(2019-02-20)
Cheng, Pei
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Liu, Yuqiang
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Chang, Sheng-Yung
;
Li, Tengfei
;
Sun, Pengyu
A tandem structure was invented to enhance photon utilization efficiency and reduce thermal loss. Considering the unique advantages of non-fullerene acceptors (NFAs), the combination of NFAs and the tandem concept shows great potential for organic photovoltaics (OPVs). Herein, a simple strategy to balance the voltage-current trade-off in tandem OPVs by employing mixed NFAs in rear sub-cells is reported. The V-OC and J(SC) of rear sub-cells can be tuned by using the blend of donor/NFA/NFA. This strategy offers an easy approach to balance the V-OC and J(SC) in tandem OPVs toward higher power conversion efficiency (PCE) without rational and careful synthesis of new materials. Tandem OPVs based on mixed NFAs in rear sub-cells exhibited the best PCE of 13.3% in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under asymptotic scans, and a PCE of 11.52% was achieved and recognized on the most recent NREL chart.
Hydrogen plasma-treated MoSe2 nanosheets enhance the efficiency and stability of organic photovoltaics
(2019-10-07)
Wang, Hao-Cheng
;
Lin, Yu-Che
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Chen, Chung-Hao
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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.
Molecular engineering of side chain architecture of conjugated polymers enhances performance of photovoltaics by tuning ternary blend structures
(2018-01-01)
Lin, Yu-Che
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Cheng, Hao-Wen
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Su, Yu-Wei
;
Lin, Bo-Hsien
;
Lu, Yi-Ju
Several approaches, including the use of small molecule acceptors, novel polymer structures, and tandem cell structures, have been adopted to prepare polymer solar cells displaying high power conversion efficiencies (PCEs). The application of ternary blends as the active layer for polymer solar cells-for which the absorption spectra can be tuned by varying the composition ratios of components-is another facile approach toward optimizing the PCEs of devices. The selection of suitable ternary blends active layer often relies on intuition and remains a formidable challenge. Here, we adopted a systemic approach of not only using the same donor chemical units in the two donor-acceptor (D/A) conjugated polymers with complementary light absorption (energy band gaps) but also varying the side chains architectures as a means of tuning the packing of these semi-planar conjugated polymers, thereby influencing the carrier transport and optimizing the PCE. We employed linear, branch and mixed linear-and-branch side-chain attached benzooxadiazole (BO) as the acceptor (A) units in poly [benzodithiophene-thiophene-benzooxadiazole] (PBDTTBO) conjugated polymers and monitored their interactions with poly[benzodithiophene-fluorothienothiophene] (PTB7-TH), both of which featured the same benzodithiophene (BDTT) donor (D) units. We found that incorporating a minor amount (10%) of D/A conjugated PBDTTBO with such side chains into the PTB7-TH with a fullerene allowed us to tune the packing of the two polymers and, thereby, enhance the PCEs of corresponding ternary blend devices; the PCE of the ternary blend device incorporating PBDTTBO with two branched-side chains, PTB7-TH, and PC71BM increased to 11.4% from 9.0% for the device incorporating only the binary blend of PTB7-TH and PC71BM-a relative increase of more than 25%. This approach of using side chain engineering to tune the structure of a minor conjugated polymer and, thus, influence the packing of another major conjugated polymer that features the same donor chemical units appears to be an effective means of preparing highly efficient polymer cells.
Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics
(2020-01-01)
Cheng, Hao-Wen
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Raghunath, Putikam
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Wang, Kai-li
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Cheng, Pei
;
Haung, Tianyi
Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.
Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component
(2019-08-01)
Cheng, Hao-Wen
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Zhang, Huotian
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Lin, Yu-Che
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She, Nian-Zu
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Wang, Rui
Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (V-OC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and V-OC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.
Unraveling Sunlight by Transparent Organic Semiconductors toward Photovoltaic and Photosynthesis
(2019-02-01)
Liu, Yugiang
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Cheng, Pei
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Li, Tengfei
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Wang, Rui
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Li, Yaowen
Because the visible and the infrared (IR) regions take up similar to 47% and similar to 51% of the energy in the solar spectrum (AM 1.5G standard), respectively, utilizing the visible light for plant growth and the IR light for power generation is potentially extremely exciting. IR-absorbing organic semiconductors, with localized IR absorption and visible-light transmittance, would be promising materials for this purpose. Here, flexible transparent organic photovoltaics (TOPVs) based on IR-absorbing organic materials were proposed, which can be a simple, low-cost, and promising way to utilize the IR light for electricity generation, and the penetrated visible light will be utilized for photosynthesis in plants. A power-conversion efficiency of similar to 10% with an average visible transmittance of 34% was achieved for TOPV devices. Meanwhile, the side-by-side comparison showed that plants grown under the TOPVs filtered light, and those under normal sunlight yielded very similar results. These outcomes demonstrated the results from TOPV devices beyond simple photovoltaic applications.
Web Application Security: Threats, Countermeasures, and Pitfalls
(2017-06-01)
Huang, Hsiu-Chuan
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Zhang, Zhi-Kai
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Cheng, Hao-Wen
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Shieh, Shiuhpyng Winston
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交大名義發表
Penetration testing is a crucial defense against common web application security threats such as SQL injection and cross-site scripting attacks. A proposed web vulnerability scanner automatically generates test data with combinative evasion techniques, significantly expanding test coverage and revealing more vulnerabilities.