Materials Science Forum Vols. 663-665

Abstract: Quasi-solid/solid polymer electrolytes have been the subject of extensive research for an alternative of liquid electrolyte for dye-sensitized solar cells (DSSCs) because of their advantages such as alleviated leakage, lower environmental impact and ease of device fabrication. In this work, the performance of the unsealed quasi-solid-state DSSCs based on composite poly (ethylene oxide) (PEO) electrolyte and N719 dye-sensitizer was examined on aging under atmospheric condition. The energy conversion efficiency of DSSC using the composite PEO electrolyte was 5.62 % under sun simulated light, AM 1.5 (100 mW cm-2) but gradually decreased to 0.95 % on aging for 90 days. An additional layer of poly(3,4-ethylenedioxythiophene) (PEDOT) electrolyte was incorporated with the composite polymer electrolyte for DSSC fabrication. The PEDOT layer was prepared by electrochemical polymerization of bis-ethylenedioxythiophene (bis-EDOT) and characterized by Raman spectroscopy and cyclic voltammetry. It was found that the energy conversion efficiency of DSSC based on the composite polymer electrolyte incorporated with PEDOT layer was 5.57 % and gradually decreased to 1.76 % under the same aging condition. Thus an additional layer of PEDOT electrolyte provided an improved stability of DSSC.

Abstract: In order to improve the performance of the dye-sensitized solar cells based on ZnO films, ZnO nanoparticles of different size and morphology were prepared by hydrothermal and solvothermal synthesis methods. Electrodes applied to dye-sensitized solar cell were prepared by the screen-printing method. The effects of ZnO nanoparticles of different size and morphology on the photovoltaic characteristics of dye-sensitized ZnO solar cells were investigated. The results show that: The short-circuit current density and the energy conversion efficiency of the ZnO nanosheets DSSC are 0.13 mA/cm2 and 0.02%. The short-circuit current density and the energy conversion efficiency of cells prepared with ZnO nanorods with diameter 500nm and length 5μm are 1.91 mA/cm2 and 0.03%.The best performance achieved in the present work was a conversion efficiency of 3.46% for the cells prepared with ZnO nanoparticles with diameters 80nm.

Abstract: By applying phosphoric acid in dispersion of fullerene in the fabrication of polypyrrolefullerene photovoltaic cells we present laminated active structure of polypyrrole and subsequent fullerene layers, with two other reference methods to incorporate fullerene: (i) in a physically blended monolayer; and (ii) in a blend from chemical reaction. I-V characteristics show that a blend monolayer cell can display photosensitive effect however without photovoltaics; a bilayer cell displays photovoltaics either in dark or in illumination, with its VOC up to1V and its JSC up to12.5 μA cm-2 under AM1 105 mW cm-2 condition. The results demonstrate that phosphoric acid is effective in dispersion of fullerene as well as combining it with polypyrrole layer in a photovoltaic cell. The effects of phosphoric acid in fabricating a bilayered photovoltaic cell are discussed mainly in terms of H-bonding.

Abstract: In this paper, vanadium oxide (V2O5) was introduced between the active layer and top electrode as buffer layer. The structure of the photovoltaic device is ITO/TiO2/P3HT: PCBM/V2O5/Ag. TiO2, which was prepared in sol-gel method, was used as an electron selective layer. The performance of photovoltaic device with V2O5 layer is dramatically improved compared with that without V2O5. The power conversion efficiency is improved from 0.79% to 2.58% under 100 mWcm2 white light illumination in ambient air.

Abstract: We present the fabrication and electric properties of MgB2 ceramic samples doped with nanosized spheres, 4-8 nm, of graphite with a metallic core. The samples were prepared using the spark plasma sintering technique. The size of the additive is comparable to the superconducting coherence length. The short processing time limits the diffusion of the carbon while keeping the core intact. Therefore, in addition to the doping with carbon, the metallic core, which has the size smaller than the superconducting coherence length, create pinning centers which might improve the dissipationless electric transport. The results are analyzed in the framework of different pinning models.

Abstract: A series of various substituted 1,3,5-triarylbenzenes, 2,4,6-triaryl-1-phenoles, 1,3,5-triaryl-1-methoxybenzenes and 2,4,6-triaryl-1,3,5-trimethoxybenzenes were synthesized by a Stille cross-coupling procedure. Their structures were confirmed by 1H NMR, 13C NMR, and elemental analysis. Containing thienyl, furyl and EDOT groups polymers obtained in the process of electropolymerization could be carefully considered as a building material in a wide range of organic-electronic devices. We compare properties of monomers and related polymers depending on aryls moieties and their influence of hydroxyl and methoxyl groups attached to the central benzene core.

Abstract: The behavior of amphiphilic block copolymers in solution has attracted considerable attention in recent years. In this paper, the self-assembly behaviors of the amphiphilic fluorinated ABC-type triblock copolymer (MeOPEO16-PSt220-PFHEA22) in different mixed solutions were studied. Also, the effect of ionic concentration on the self-assembly aggregates of the copolymer in toluene-ethanol-water was studied.

Abstract: Ti1-xFexO2 nanocrystals with x = 0.01, 0.02, 0.03 were prepared via a nonaqueous synthesis route. X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy characterization confirmed the formation of anatase-phase nanocrystals with the average crystallite sizes of around 10 nm. The lattice constants alternate with the increase of the Fe content and no iron clusters were generated. X-ray photoelectron spectroscopy measurements showed that the substitutional Fe ions present mainly the valence of +3. The magnetic hysteresis loops measured at room temperature (RT) 300K showed that all the doped samples are atypically ferromagnetic, and the coercivity (Hc) of all the Fe-doping samples is around 0.1 T. An interpretation for the intrinsic RT ferromagnetism is put up based on the free carriers and defects induced interaction between Fe3+ ions.

Abstract: In this paper, according to the model proposed by Wagner et al., the properties of the magnetically aligned clusters in rare earth manganite Nd0.52Sr0.48MnO3 film are investigated. As we all have known, even at the same temperature and in the same external magnetic field the colossal magnetoresistivity (CMR) effects of different manganites are different. Through imitating the variation of the magnetoresistance (MR) with respect to some physics parameters, the built-in factors that can influence the value of MR and the field sensitivity are analyzed. The investigations show that the CMR effects, to some extent, can be governed by the size of the magnetically aligned clusters. In addition, through analyzing the different magnetoresistance scaling in different magnetic phases it is found that with the paramagnetic-ferromagnetic transition a sudden change in the size of the magnetically aligned clusters occurs, the physical origin of which are explored.

Abstract: Hybrid Graphene-ZnS nanopaticles (G-ZnS NPs) were prepared by using a solvothermal method. A dispersion of graphite oxide (GO) and zinc acetate dihydrate (Zn(CH3COO)2.2H2O) in dimethl sulfoxide (DMSO) reacted at 180 °C for 12 h in a Telfon-lined stainless steel autoclave. In the reaction, DMSO serves as a sulphide source as well as a reducing agent, resulting formation of the hybrid G-ZnS NPs in one-step. Hybrid G-ZnS NPs were characterized by using a powder X-ray diffractometer, a Fourier-transform infrared spectrometer, a transmission electron microscope, a UV-vis spectrophotometer and a fluorescence spectrophotometer, respectively. In the FTIR spectra, the GO related stretching bands of C-O and carboxyl groups are not observed in the spectra of G-ZnS, suggesting that the GO sheets were reduced to graphene sheets. In the TEM images, it is observed that the ZnS nanoparticles with an average size of 23 nm are attached onto the graphene sheets. The UV-vis absorption spectrum of the G-ZnS NPs dispersed in ethanol has an absorption peak of G at 261 nm and a weak shoulder of ZnS NPs around 320 nm. The broadening and weakening of the peak of ZnS NPs at 320 nm arises from the interparticle coupling effect. Under excitation at 225 nm, a peak around 386 nm and other weaker bands appear in the fluorescence spectrum of the G-ZnS. The band at 386 nm is attributed to zinc vacancies.