Browsing by Author "Boopathi, Karunakara Moorthy"

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A dual-functional additive improves the performance of molecular bulk heterojunction photovoltaic cells
(2014)
Farahat, Mahmoud E.
;
Wei, Hung-Yu
;
Ibrahem, Mohammed Aziz
;
Boopathi, Karunakara Moorthy
;
Wei, Kung-Hwa
In this paper we report a simple and effective approach towards improving the performance of molecular bulk heterojunction (BHJ) photovoltaics through incorporation of a new, nonvolatile processing additive; (3-chloropropyl) trimethoxysilane (CP3MS). A small amount of the additive CP3MS combined with post-annealing treatment significantly enhanced the power conversion efficiency (PCE) of dialkylated diketopyrrolopyrrole chromophore (SMDPPEH)-based molecular BHJ solar cells. The PCE increased from 2.75% for a device prepared without the additive or annealing to 4.55% for a device containing 0.1% CP3MS that had been subjected to post-annealing treatment at 100 degrees C for 10 min. CP3MS performed an interesting dual function when incorporated as an additive in molecular BHJ devices. The first was that it controlled the morphology: the addition of 0.1% CP3MS to the SMDPPEH: PC61BM blend was sufficient to improve the film's crystallinity and morphology. The second function was the spontaneous migration of the CP3MS molecules from the bulk to the interface between the active layer and the Al cathode, forming an ultrathin interlayer that acted as a buffer layer suppressing charge recombination and enhancing charge transport at the interface. Analyses using atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, together with examinations of device performance, confirmed the dual-functional nature of CP3MS as an additive. CP3MS also showed its promising ability to enhance the performance of different blend systems. The performance of benzodithiophene (BDT)-based molecular solar cells enhanced from 3.05% without additive to 3.8% with the incorporation of 0.1% CP3MS.
A high performance electrochemical sensor for acetaminophen based on a rGO-PEDOT nanotube composite modified electrode
(2014)
Huang, Tzu-Yen
;
Kung, Chung-Wei
;
Wei, Hung-Yu
;
Boopathi, Karunakara Moorthy
;
Chu, Chih-Wei
In this study, we perform an electrochemical sensing using a conductive composite film containing reduced graphene oxide (rGO) and poly(3,4-ethylenedioxythiophene) nanotubes (PEDOT NTs) as an electrode modifier on a glassy carbon electrode (GCE). Scanning electron microscopy suggests that the rGO covers the surface of GCE uniformly and the PEDOT NTs act as a conducting bridge to connect the isolated rGO sheets. By combining these two materials, the conductivity and the surface coverage of the film can be enhanced, which is beneficial for electrochemical sensing. The rGO-PEDOT NT composite modified electrode is applied for an effective sensor to analyze acetaminophen. The obtained electrochemical activity is much higher than those obtained by the rGO-and PEDOT NT-modified electrodes; the higher electrochemical activity may be attributed to the higher conductivity and greater coverage of the rGO-PEDOT NT composite film on the GCE. Furthermore, interference tests indicate that the rGO-PEDOT NT composite modified electrode exhibits high selectivity toward the analyte. This novel method for combining the rGO and PEDOT NTs establishes a new class of carbon material-based electrodes for electrochemical sensors.
A novel ball milling technique for room temperature processing of TiO2 nanoparticles employed as the electron transport layer in perovskite solar cells and modules
(2018-04-28)
Singh, Mriganka
;
Chiang, Chien-Hung
;
Boopathi, Karunakara Moorthy
;
Hanmandlu, Chintam
;
Li, Gang
Anatase titanium dioxide (an-TiO2) is often used as the electron transporting material (ETM) in planar-heterojunction perovskite solar cells (PSCs) because of its excellent semiconductor characteristics, outstanding optical transmittance, and suitable band structure. Herein, we report an inexpensive method for mass-scale production of TiO2 ETMs at room temperature (RT similar to 30 degrees C), involving the grinding of large clumps of an-TiO2 to form a suspension of TiO2 nanoparticles (NPs) in isopropyl alcohol for meso-superstructured PSCs. This process does not involve any chemical synthesis; it is a purely physical process. The lowest unoccupied molecular orbital (LUMO) of ground an-TiO2 NPs, estimated using ultraviolet photoelectron spectroscopy (UPS), was ca. 4.06 eV, which is a salient feature for the active layer. A regular perovskite solar cell (PSC) based on a CH3NH3PbI3 absorber and ground an-TiO2 ETL exhibited a champion power conversion efficiency (PCE) of 17.43% with an active area of 0.1 cm(2). The same ground an-TiO2 NPs were used to fabricate a large-area (designated area: 25.2 cm(2)) PSC and a PCE of 14.19% was achieved. PSC devices incorporating the ground an-TiO2 NP ETLs exhibited an attractive long-term device stability, with the PCE retaining approximately 85% of the initial values after 80 days.
Controlled mechanical cleavage of bulk niobium diselenide to nanoscaled sheet, rod, and particle structures for Pt-free dye-sensitized solar cells
(2014)
Ibrahem, Mohammed Aziz
;
Huang, Wei-Chih
;
Lan, Tian-wey
;
Boopathi, Karunakara Moorthy
;
Hsiao, Yu-Chen
In this study, we report a one-step process for the preparation of NbSe2 nanosheets, nanorods and nanoparticles from pristine materials under the effects of shear and friction forces. Nevertheless, simple and facile methods for the large-scale syntheses of well-defined NbSe2 nanostructures in high yield have yet to be realized and that will have a great impact in a wide range of applications. For example, developing platinum (Pt)-free and highly efficient counter electrodes is meaningful and necessary for the cost reduction of dye-sensitized solar cells (DSSCs). By integrating this approach with a simple method of thin film preparation (spray coating) allowed us to prepare large-area, conductive, semitransparent flexible thin films of NbSe2. We have used microscopic and macroscopic methods to examine the morphologies, compositions, crystallinity, and electrical and optical properties of the converted NbSe2 nanostructures. DSSCs with NbSe2 nanosheet counter electrodes (CEs) achieved a conversion efficiency of 7.73%, superior to an efficiency of 7.01% for Pt-based CEs. Our NbSe2 nanostructure provides a cost-effective CE alternative to the noble metal Pt in DSSCs.
Mitigating Metal Dendrite Formation in Lithium-Sulfur Batteries via Morphology-Tunable Graphene Oxide Interfaces
(2019-01-16)
Chen, Yu-Ting
;
Abbas, Syed Ali
;
Kaisar, Nahid
;
Wu, Sheng Hui
;
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.
Solution-processable bismuth iodide nanosheets as hole transport layers for organic solar cells
(2014-02-01)
Boopathi, Karunakara Moorthy
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Raman, Sankar
;
Mohanraman, Rajeshkumar
;
Chou, Fang-Cheng
;
Chen, Yang-Yuang
In this paper we demonstrate the use of low-temperature-solution-processable bismuth iodide (BiI3) nanosheets as hole transport layers in organic photovoltaics with an active layer comprising poly(3-hexylthiophene) (P3HT) mixed with a fullerene derivative. The performance of the resulting devices was comparable with that of corresponding conventionally used systems incorporating polyethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS). UV-vis spectroscopy revealed that the transparency of a BiI3 layer in the visible ( > 620 nm) and near-infrared range is greater than that of a PEDOT:PSS layer. X-ray photoemission spectroscopy of a BiI3 film revealed signals at 158.8, 164, 618.6, and 630 eV-characteristic of Bi 4f(7/2), Bi 4f(5/2), I 3d(5/2), and I 3d(3/2), respectively-that indicated a stoichiometric BiI3 film. Wet milling of BiI3 crystals resulted in the formation of nanosheets, the presence of which we confirmed using scanning electron microscopy. The resultant power conversion efficiency of the device was approximately 3.5%, with an open-circuit voltage of 0.56 V, a short-circuit current density of 10.4 mA cm(-2), and a fill factor of 60.1% under AM1.5G irradiation (100 mW cm(-2)). (C) 2013 Elsevier B.V. All rights reserved.
Synthesis of fluorinated benzotriazole (BTZ)- and benzodithiophene (BDT)-based low-bandgap conjugated polymers for solar cell applications
(2017-04)
Pola, Murali Krishna
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Boopathi, Karunakara Moorthy
;
Padhy, Harihara
;
Raghunath, Putikam
;
Singh, Ashutosh
A series of donor acceptor (D-A) polymers (P1-P3) based on benzodithiophene (BDT) and electron- accepting benzotriazole (BTZ) units containing thiophene linkers with/without alkyl side-chains were designed and synthesized via Stille coupling polymerization method. The effects of polymers with multiple fluorinated BTZ groups on their thermal, optical, electrochemical, and photovoltaic properties were investigated. These polymers possessed the highest occupied molecular orbital (HOMO) levels ranged -5.38 to -5.6 eV and the lowest unoccupied molecular orbital (LUMO) levels ranged -3.55 to -3.57 eV, which covered broad absorption ranges with low optical bandgaps. The bulk heterojunction (BHJ) polymer solar cell (PSC) devices containing an active layer of D-A polymers blended with different weight ratios of electron-acceptor [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) were explored under 100 mW cm(-2) of AM 1.5 white-light illumination, where the maximum power conversion efficiency (PCE) value of 3% (with J(sc) = 7.70 mA/cm(2), FF = 54.04, and V-oc = 0.72 V) was obtained in the PSC device consisting of polymer P3. (C) 2016 Elsevier Ltd. All rights reserved.