Browsing by Author "Ibrahem, Mohammed Aziz"

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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.
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.
Direct conversion of multilayer molybdenum trioxide to nanorods as multifunctional electrodes in lithium-ion batteries
(2014)
Ibrahem, Mohammed Aziz
;
Wu, Feng-Yu
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Mengistie, Desalegn Alemu
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Chang, Chia-Seng
;
Li, Lain-Jong
In this study we prepared molybdenum trioxide (MoO3) nanorods having average lengths of 0.5-1.5 mu m and widths of approximately 100-200 nm through a one-step mechanical break-down process involving favorable fracturing along the crystal direction. We controlled the dimensions of the as-prepared nanorods by applying various imposing times (15-90 min). The nanorods prepared over a reaction time of 90 min were, on average, much shorter and narrower relative to those obtained over 30 min. Evaluations of lithium-ion storage properties revealed that the electrochemical performance of these nanorods was much better than that of bulk materials. As cathodes, the nanorods could deliver a high specific capacity (>315 mA h g(-1)) with losses of less than 2% in the first cycle at a rate of 30 mA g(-1); as anodes, the specific capacity was 800 mA h g(-1) at a rate of 50 mA g(-1). Relative to alpha-MoO3 microparticles, these nanorods displayed significantly enhanced lithium-ion storage properties with higher reversible capacities and better rate performance, presumably because their much shorter diffusion lengths and higher specific surface areas allowed more-efficient insertion/deinsertion of lithium ions during the charge/discharge process. Accordingly, enhanced physical and/or chemical properties can be obtained through appropriate nanostructuring of materials.
High quantity and quality few-layers transition metal disulfide nanosheets from wet-milling exfoliation
(2013)
Ibrahem, Mohammed Aziz
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Lan, Tian-wey
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Huang, Jing Kai
;
Chen, Yang-Yuan
;
Wei, Kung-Hwa
Low-cost and large-area electronic applications require the deposition of active materials in simple and inexpensive techniques at room temperature; properties usually associated with polymer films. In this study, we demonstrate a simple, low-cost and environmentally friendly method for the high-yield production of two dimensional nanosheets of semiconducting transition metal disulfides, integrated with the route towards the solution-processed deposition of MoS2 and WS2 thin films. The resulting materials with high purity and no contamination or distortion in their structural and electronic properties were confirmed with different microscopic and macroscopic methods. As a proof of concept, we utilize these layered transition metal disulphide films as electron extraction layers in an inverted structure organic solar cell, prepared at relatively low annealing temperatures (<= 150 degrees C). A promising power conversion efficiency with high stability is achieved, which makes these proposed buffer layers quite attractive for next-generation flexible devices requiring high conductivity and transparency, as well as wide range of other potential applications.
Interfacial engineering affects the photocatalytic activity of poly(3-hexylthiophene)-modified TiO2
(2013)
Huang, Jen-Hsien
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Ibrahem, Mohammed Aziz
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Chu, Chih-Wei
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光電工程學系
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Department of Photonics
In this study, oxidation polymerization was used to synthesize poly(3-hexylthiophene) (P3HT)-modified TiO2 nanoparticles (NPs) and then the effect of the interface between the TiO2 NPs and the P3HT coating on the system's photocatalytic ability under visible light was investigated. The photocatalytic properties of the TiO2 NPs were enhanced from the UV to the visible after incorporation of P3HT. Moreover, charge transfer between the TiO2 NPs and the P3HT coating was promoted when a self-assembled monolayer (SAM) of 2-thiophenecarboxylic acid was present at their interface; this SAM decreased the barrier for charge transfer between the TiO2 NPs and the P3HT coating, leading to improved photocatalytic activity under visible light.
Solution-processed zinc oxide nanoparticles as interlayer materials for inverted organic solar cells
(2013-01-01)
Ibrahem, Mohammed Aziz
;
Wei, Hung-Yu
;
Tsai, Meng-Hung
;
Ho, Kuo-Chuan
;
Shyue, Jing-Jong
This paper describes inverted bulk heterojunction organic solar cells featuring solution-processed zinc oxide nanoparticles (ZnO NPs) as an electron extraction layer, prepared at relatively low annealing temperatures (<= 150 degrees C). A solution of ZnO NPs (average size: 25 nm) was prepared using a wet grinding method. When the ZnO interlayer was present in the solar cell, the vertical phase separation of the active layers prepared with and without solvent annealing exhibited similar gradient concentrations and, therefore, similar photocurrent generation, both of which were superior to those of conventional devices incorporating a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) hole extraction layer. We attribute this vertical phase separation to the similar surface energies of the fullerene derivative and the ZnO interlayer. Under simulated air mass (AM) 1.5 G illumination at 100 mW cm(-2), the power conversion efficiency of the optimized device was approximately 4%. (C) 2012 Elsevier B.V. All rights reserved.
Wet-milled anatase titanium oxide nanoparticles as a buffer layer for air-stable bulk heterojunction solar cells
(2015-08-01)
Huang, Jen-Hsien
;
Ibrahem, Mohammed Aziz
;
Chu, Chih-Wei
;
光電工程學系
;
Department of Photonics
In this study, an air-stable bulk heterojunction organic solar cell demonstrated by utilization of titanium oxide (TiO2) nanoparticles as a hole blocking layer was prepared through high-energy grinding method. The large clumps of the anatase TiO2 underwent deaggregation to form a stable dispersed solution during the grinding process. The resultant suspension can form a uniform and smooth TiO2 film through spin coating on various substrates. Because of substantial oxygen and water protection effect of TiO2 thin film, the bulk heterojunction solar cells exhibit a significant long-term stability. It is also found that the cell performance can be promoted dramatically after ultraviolet activation. The mechanism responsible for the enhanced cell efficiency was also investigated. This solution-based method does not require surfactants, thus preserving the intrinsic electronic and optical properties of TiO2 that makes these proposed buffer layers quite attractive for next-generation flexible devices appealing high conductivity and transparency. Copyright (c) 2014 John Wiley & Sons, Ltd.