Composite Active Layer Research Articles

Highly Sensitive Flexible Human Motion Sensor Based on ZnSnO3/PVDF Composite

A highly sensitive body motion sensor has been fabricated based on a composite active layer of zinc stannate (ZnSnO3) nano-cubes and poly(vinylidene fluoride) (PVDF) polymer. The thin film-based active layer was deposited on polyethylene terephthalate flexible substrate through D-bar coating technique. Electrical and morphological characterizations of the films and sensors were carried out to discover the physical characteristics and the output response of the devices. The synergistic effect between piezoelectric ZnSnO3 nanocubes and β phase PVDF provides the composite with a desirable electrical conductivity, remarkable bend sensitivity, and excellent stability, ideal for the fabrication of a motion sensor. The recorded resistance of the sensor towards the bending angles of −150° to 0° to 150° changed from 20 MΩ to 55 MΩ to 100 MΩ, respectively, showing the composite to be a very good candidate for motion sensing applications.

A composite light-harvesting layer from photoactive polymer and halide perovskite for planar heterojunction solar cells.

A new route for fabrication of photoactive materials in organic-inorganic hybrid solar cells is presented in this report. Photoactive materials by blending a semiconductive conjugated polymer with an organolead halide perovskite were fabricated for the first time. The composite active layer was then used to make planar heterojunction solar cells with the PCBM film as the electron-acceptor. Photovoltaic performance of solar cells was investigated by J-V curves and external quantum efficiency spectra. We demonstrated that the incorporation of the conjugated photoactive polymer into organolead halide perovskites did not only contribute to the generation of charges, but also enhance stability of solar cells by providing a barrier protection to halide perovskites. It is expected that versatile of conjugated semi-conductive polymers and halide perovskites in photoactive properties enables to create various combinations, forming composites with advantages offered by both types of photoactive materials.

Mechanisms of radiative recombination in ambipolar light-emitting field-effect transistors based on organic polymers and inorganic nanoparticles

Mechanisms of radiative recombination in ambipolar light-emitting field-effect transistors with composite active layers based on the PFO organic polymer and inorganic ZnO nanoparticles are considered. Theoretical analysis of the radiative recombination in the accumulation layer of the structure is performed in the framework of a model permitting one to obtain an analytical description of the process. An expression for the total recombination rate has been obtained and numerical calculations have been carried out. Correspondence between the calculation results and experimental data has been obtained for the integral intensity of electrical luminescence in the composite structure under consideration.

Enhanced efficiency of organic solar cells based on (MEH-PPV) with graphene and quantum dots

In this work, organic photovoltaic cells are fabricated using a spin coated composite active layer of organic electronic materials conjugated polymer poly[2-methyl-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) mixed with cadmium selenide (CdSe) quantum dots and graphene. The active layer is sandwiched between two metallic conductors, typically a layer of silicon and indium tin oxides (SiO2:ITO) with high work function of (4.3 eV) and a layer of low work function aluminum metal (3.7 eV) as anode and cathode respectively. Spectral properties were explored for thin films of pure MEH-PPV, CdSe, MEH-PPV:CdSe, and MEH-PPV:CdSe:graphene blends coated onto glass at a spin speed of 6000 rpm using a spectrophotometer for optical absorption in the visible region with various concentration and benzene as a solvent. The photoluminescence (PL) spectra of the pure quantum dots and blended MEH-PPV:CdSe with graphene from various concentrations were recorded. The current–voltage characteristics (I–V) of the solar cells showed that incorporation of the quantum dots and graphene in the copolymer resulted into further increase in the power conversion efficiency compared to that in their absence.

Light-emitting transistor structures based on semiconducting polymers and inorganic nanoparticles

One of the new directions in organic electronics is the development of light-emitting organic field-effect transistors, which combine the light-emitting properties of organic light-emitting diodes and the switching properties of organic field-effect transistors. Optical and electronic properties of novel nanocomposite materials based on semiconducting polymers and inorganic nanoparticles and designed for applications in organic electronics devices were investigated. Light-emitting organic field-effect transistors with composite active layers based on the soluble semiconducting polymers PFO and MEH-PPV and ZnO nanoparticles and having asymmetric electrodes (Al and Au) that inject electrons into ZnO and holes into PFO and MEH-PPV were prepared and investigated. The data are interpreted in the context of the possibility of organic field-effect transistors based on PFO: ZnO and MEH-PPV: ZnO composite films to work in both the unipolar regime and the ambipolar regime. It is shown that the mobility of charge carriers in light-emitting organic field-effect transistors based on PFO: ZnO at 300 K reaches ∼0.02 for electrons and ∼0.03 cm2/(V s) for holes, increasing with an increase in the concentration of nanoparticles up to ∼2 cm2/(V s), a value that is comparable to the maximum mobility values for conducting polymers. Light-emitting organic field-effect transistors based on PFO: ZnO and MEH-PPV: ZnO emit light in the green and orange ranges of the optical spectrum, respectively, their electroluminescence intensities rising with an increase in either the negative bias or the positive bias at the source-drain and the gate as well as with an increase in the concentration of ZnO nanoparticles. The results indicate that light-emitting organic field-effect transistors based on soluble conjugated polymers and semiconducting ZnO nanoparticles are examples of multifunctional devices whose production technology is compatible with the modern ink-jet printing technology of organic electronics.

Polymeric Solar Cells Efficiency Increase Using Doped Conjugated Polymer Nanoparticles

Organic photovoltaic cells are made by sandwiching a composite active layer of organic electronic materials conjugated copolymer (BEHP-co-MEH-PPV) mixed with ZnO nanoparticles, between two metallic conductors, typically a layer of indium tin oxide (ITO) with high work function( 4.8 eV) and a layer of low work function metal(3.7eV) such as Aluminum. In this work, the spin coated conjugated copolymer blends (BEHP-co-MEHPPV): ZnO thin films, deposited on both Silicon and glass substrates have been studied for morphology using atomic force microscopy (AFM). All films examined by AFM, showed a dense structure with average roughness of 20 -40 nm. Optical properties were explored for films coated onto glass substrates at a spin speed of 1200 rpm, using a spectrophotometer for optical absorption in the visible region. The photo luminescence (PL) spectra of the pure and blended BEHP-co-MEH-PPV films were recorded. Ellipsometry were used for refractive index, extinction coefficient and thickness. The current-voltage characteristics (I-V’s) of the solar cell showed that incorporation of the ZnO nanoparticles in the copolymer resulted into further increase in the power conversion efficiency compared to that in their absence. All deposited films showed good adhesion to substrates, and good optical properties. The conductivity of the active layer increases with the increment of the ZnO nanoparticles into Original Research Article British Journal of Applied Science & Technology, 4(4): 604-616, 2014 605 the nanocomposite thin films. Such characteristics make the polymer: nanoparticle blended layer (BEHP-co-MEHPPV: ZnO) very favourable to charge injection and conduction for photovoltaic device.

Graphene/Au composite paper as flexible current collector to improve electrochemical performances of CFx cathode

We report the application of free-standing, lightweight, and flexible graphene/Au composite paper (GACP), as a current collector for CFx cathode. At a high discharge current density of 4000 mA g−1 (5C), the capacity of the CF1.0 loaded on GACP current collector is 653 mAh g−1, while CF1.0 loaded on Al foil failed at 800 mA g−1 (1C). Using GACP, both excellent rate capability and specific capacity can be achieved simultaneously, owing to its undulant surface structure and flexible contact with the CFx composite active layer. Our results provide a new strategy to design both high power and energy densities CFx cathode.

Effects of Organic Solvents for Composite Active Layer of PCDTBT/PC71BM on Characteristics of Organic Solar Cell Devices

Bulk heterojunction (BHJ) structure based active layers of PCDTBT/PC71BM were prepared by using different organic solvents for fabrication of organic solar cell (OSC) devices. Mixture of precursor solutions of PCDTBT/PC71BM in three different organic solvents was prepared to fabricate composite active layers by spin-coating process: chloroform; chlorobenzene; o-dichlorobenzene. Four different blend ratios (1 : 3–1 : 6) of PCDTBT: PC71BM were adopted for each organic solvent to clarify the effect on the resulting OSC device characteristics. Surface morphology of the active layers was distinctively affected by the blend ratio of PCDTBT/PC71BM in organic solvents. Influence of the blend ratio of PCDTBT/PC71BM on the OSC device parameters was discussed. Performance parameters of the resulting OSC devices with different composite active layers were comparatively investigated. Appropriate blend ratio and organic solvent to achieve better OSC device performance were proposed. Furthermore, from the UV-Vis spectrum of each active layer prepared using the PCDTBT/PC71BM mixed solution dissolved with different organic solvents, a possibility that the nanophase separation structure inside their active layer could appear was suggested.

Improved efficiency of solar cells based on BEHP-co-MEH-PPV doped with ZnO nanoparticles

Organic photovoltaic cells are made by sandwiching a composite active layer of organic electronic materials conjugated copolymer (BEHP-co-MEH-PPV) mixed with ZnO nanoparticles, between two metallic conductors, typically a layer of indium tin oxide (ITO) with high work function (4.8eV) and a layer of low work function metal (3.7eV) such as aluminium. In this work, the spin coated conjugated copolymer blends (BEHP-co-MEH-PPV): ZnO thin films, deposited on both silicon and glass substrates, have been studied for morphology using atomic force microscopy (AFM). All films examined by AFM, showed a dense structure with average roughness of 20–40nm.Optical properties were explored for films coated onto glass substrates at a spin speed of 1200rpm, using a spectrophotometer for optical absorption in the visible region. The photo luminescence (PL) spectra of the pure and blended BEHP-co-MEH-PPV films were recorded. Ellipsometry were used for refractive index, extinction coefficient and thickness. The current–voltage characteristics (I–V's) of the solar cell showed that incorporation of the ZnO nanoparticles in the copolymer resulted into further increase in the power conversion efficiency compared to that in their absence.All deposited films showed good adhesion to substrates, and good optical properties. The conductivity of the active layer increases with the increment of the ZnO nanoparticles into the nanocomposite thin films. Such characteristics make the copolymer: nanoparticle blended layer (BEHP-co-MEHPPV: ZnO) very favourable to charge injection and conduction for photovoltaic devices.

LNF SOFC cathodes with active layer using Pr6O11 or Pr-doped CeO2

We fabricated electrolyte supported single cells with three types of cathodes that consisted of a Ce0.1Gd0.1O1.95 (GDC) buffer layer, a LaNi0.6Fe0.4O3 (LNF) cathode and an active layer. The only difference between the three cathodes was that each had a different active layer, namely a GDC–LNF composite active layer (our conventional cathode), a PrxCe1–xO2–δ (x = 0.1, 0.3, 1.0)–LNF composite active layer and a Pr6O11 (PrxCe1–xO2–δ (x = 1.0)) active layer. The interface resistance, Rinf, and overvoltage, ηc, of the cathodes were investigated. At 800 °C, the Rinf of the cathode with the Pr6O11 active layer was reduced to 1/30 that of the cathode with the GDC–LNF composite active layer. The Rinf at 800 °C for the cathode with the Pr6O11–LNF composite active layer was reduced to 1/8 that of the cathode with the GDC–LNF composite active layer. The Rinf values of the cathode with an active layer between 650 and 750 °C were also much better than those of the cathode with the GDC–LNF composite active layer. By using the cathode with the Pr6O11 active layer, the operating temperature can be reduced to 700 °C while retaining the same performance (same overvoltage at 254 mA/cm2) as a cathode with a GDC–LNF composite active layer at 800 °C.We also investigated the reactions at the interfaces in the sintering process. X-ray diffraction (XRD) analysis revealed that the Pr6O11 reacted easily with zirconia, and Pr2Zr2O7 was produced at 1000 °C or above. It was suggested that the sintering temperature of the cathodes with the active layer could be increased to around 1000 °C without any reaction at the interface between Pr6O11 and other materials.

Nanocomposite substrates for controlling internal concentration polarization in forward osmosis membranes

Forward osmosis (FO) is an emerging membrane separation technology with many potential applications. The water flux performance of existing FO membranes is largely limited by the internal concentration polarization (ICP) of solutes in their porous substrates. The current study investigated the use of nanocomposite substrates for controlling ICP and thus improving FO water flux. Polysulfone-nanocomposite (PSfN) substrates were prepared via phase inversion by incorporating porous zeolite nanoparticles in polysulfone. The PSfN0.5 (with 0.5wt% zeolite loading) substrate showed improved surface porosity and hydrophilicity. A thin film composite (TFC) polyamide active layer was prepared by interfacial polymerization on the PSfN0.5 substrate, and the resulting TFC-PFSN0.5 membrane showed significantly enhanced water permeability compared to the TFC membrane prepared on a conventional polysulfone substrate. Under identical testing conditions, the FO water flux of the TFC-PFSN0.5 membrane was more than doubled of that of the conventional TFC membrane. Using 2M NaCl as draw solution (DS) and 0–0.01M NaCl as feed solution (FS), PSfN0.5-TFC had an FO water flux as high as ∼80LMH in the active layer facing DS (AL–DS) orientation and ∼40LMH in the AL–FS orientation. Further analysis revealed that the incorporation of zeolite nanoparticles significantly reduced the substrate structural parameter (S=0.34mm for PSfN0.5-TFC compared to 0.96mm for TFC). The current study demonstrates for the first time the use of porous particles and nanocomposite substrates for controlling ICP in FO operation.

Heat generation in 1–3 piezoceramic—polymer composites

This paper describes the mechanism of heat generation in lossy 1–3 piezoceramic- polymer composite active layer of ultrasonic transducers excited at different voltages at resonance and off-resonance frequencies. The physical parameters controlling the heat generation and dissipation are estimated by least squares fitting the experimentally measured time-temperature profiles to a theoretical model. The theoretical profiles agree well with the measured data. The temperature rise at resonance frequency (250 kHz) and at an off-resonance frequency (30 kHz) is found to be 54 °C at 13.2 Vp-p and 38 °C at 169 Vp-p, respectively. The temperature rise, the total loss and the radiation heat transfer coefficient are found to vary quadratically with driving electric field. The convection heat transfer coefficient is estimated to be in the range (6–10) Wm−2 K−1, validating the free convection in air. Variations in the physical parameters with applied voltage are found to be different at resonance and off-resonance frequencies, indicating that the process of heat generation in piezocomposite transducers depends on the frequency region in which they are operated, with respect to the resonance frequencies.

Effects of Annealing Conditions on ZnO Buffer Layer for Inverted Polymer Solar Cells

A solution-processed zinc oxide (ZnO) thin film as the buffer layer with optimized processes especially the annealing conditions for inverted polymer solar cells (PSCs) has been demonstrated. Firstly the thickness of ZnO buffer layer was optimized, and different annealing conditions including temperature and time have also been taken into consideration. And the best Power Conversion Efficiency (PCE) 3.434% was observed when the ZnO buffer layer was spin–coated at 1500 rpm and annealed at 275℃ for 5 min, and AFM results showed that morphology of this ZnO film has the best uniformity which was beneficial to form high quality polymer composite active layer.

Research on a cylindrical cloak with active acoustic metamaterial layers

Enlightened by the tunable properties of effective density of the active acoustic metamaterial, we design an active infinite cylinder acoustic cloak according to the idea of the multilayer structured acoustic cloak with homogeneous isotropic materials. Utilizing the electrical analog, the dynamical equation of the acoustic cavity with Piezo-Diaphragm is presented. By analyzing the circuit diagram, the control strategy of achieving various effective densities which are used for constructing the acoustic cloak is given. Based on the necessary parameters such as the wide range values of the relative densities gained by active control, and the acoustic speed of each composite layer, the acoustic pressure field of the plane wave incident on the cloak is calculated, via the FEM model. Also the pressure map of a rigid cylinder scatterer with surrounded fluid is performed for comparison. Results show that outside the cloaking shell, the plane wave field is almost undisturbed. However inside the shell, the plane wavefronts are gradually deflected, and guided around the cloaked domain, returning to the original plane shape with small perturbation. This phenomenon making the cloak acoustically invisible in some frequency ranges has useful values in engineering applications. Finally, the total scattering cross section of the cloak is calculated to investigate the invisible effect according to the frequency domain. The total number of the composite active metamaterial layers is 15, which is much easier to realize in experiment.

High temperature properties of Ce 1- xPr xO 2-δ as an active layer material for SOFC cathodes

We prepared Ce 1-xPr xO 2-δ and investigated its high temperature properties as a material for the composite active layer of a solid oxide fuel cell (SOFC) cathode. We found that increasing the Pr concentration increases the total conductivity and oxygen vacancy concentration at high temperature, and this may lead to improvement of the cathodic reaction. When Ce 1-xPr xO 2-δ is heated, it expands significantly at a certain temperature (T inf), and this expansion depends on the Ce 1-xPr xO 2-δ composition. The expansion is associated with an abrupt increase in the unit cell volume of the cubic structure. Abrupt increases in the total conductivity and oxygen vacancy concentration were also observed at T inf. These results can be explained by oxygen vacancy and electron formation (n-type electronic conductivity increase) at T inf and above T inf. A sample with a Ce 1-xPr xO 2-δ composition where x = 1.0 has no such T inf. A composition near x = 1.0 for Ce 1-xPr xO 2-δ is favorable for the active layer material of an SOFC cathode, because of the high conductivity and high concentration of oxygen vacancies.

Controlling the morphology of trioctyl phosphine oxide-coated cadmium selenide/poly 3-hexyl thiophene composite active layer for bulk hetero-junction solar cells

Bulk hetero-junction solar cells with CdSe nanoparticles-P3HT (poly 3-hexyl thiophene) composite active layer were fabricated, and the control of morphological feature of the nanoparticle-polymer composite thin films was investigated. A binary solvent composed of a primary solvent with intermediate polarity and a secondary solvent with high polarity was found to be effective in controlling the dispersion of the CdSe nanocrystals in the P3HT matrix, and the modification of the nanocrystal surface by liquid-liquid extraction process was found to be effective in achieving the desired composite film morphology. Surface roughness of the active layer was optimized for various loadings of CdSe nanoparticles and could be reproducibly controlled to less than 10 nm.

Effect of CdSe/P 3HT composition on electrical and structural properties of bulk hetero-junction solar cell active layer

The use of inorganic nano-semiconductor/polymer blend as the active layer for organic bulk hetero-junction solar cell is an alternative to change and improve the device characteristics and performance. Effects of CdSe/P 3HT composition in the blend and its loading amount in the solvent on the electrical and structural properties of active layers formed were investigated. The results of atomic force microscopy study indicated that the surface roughness of composite active layer could be controlled below 10 nm for the entire range of composite loading amount investigated in this study. The transmission line method experiments have demonstrated that the electrical percolation pathways could be developed at the critical loading amount of CdSe/P 3HT composite, resulting in the abrupt decrease of sheet resistance and significant increase in the power conversion efficiency of ITO/PEDOT:PSS/(CdSe/P 3HT)/Al solar cell.

Cost-Effective Single Step Cofiring Process for Manufacturing Solid Oxide Fuel Cells Using HSC™ Anode

The anode-supported planar solid oxide fuel cell (SOFC) was fabricated by a cost-effective single step cofiring process using high shear compaction (HSC)™ anode substrate. The HSC™ process is a novel ceramic tape fabrication technique, which offers advantages in low-cost and high-volume production of the anode substrates over the conventional tape forming processes. The cell was comprised of a porous HSC™ Ni+8 mol % yttria-stabilized zirconia (YSZ) anode substrate, a porous Ni+YSZ anode barrier layer, a porous and fine-grained Ni+YSZ anode active layer, a dense YSZ electrolyte, a porous and fine-grained Ca-doped LaMnO3(LCM)+YSZ composite cathode active layer, and a porous LCM cathode current collector layer. The fabrication process involved wet powder spraying of the anode barrier layer over the HSC™ anode substrate followed by screen-printing of the remaining component layers. The cell was then cofired at 1340°C for 2 h. The microstructure and the open circuit voltage of the cell confirmed that the cell was crack-free and leak-tight. The cofired cell showed a stable and acceptable electrochemical performance at 800°C under humidified hydrogen (3–60% H2O) as fuel and air as oxidant. The anode active layer with finer and less porous microstructure increased the triple phase boundary length and improved cell performance under conditions that simulated higher fuel utilization. The material system and fabrication process presented in this work offers great advantage in low-cost and high-volume production of SOFCs, and it can be the basis for scale-up and successful commercialization of the SOFC technology.

An SOFC Cathode Composed of LaNi0.6Fe0.4O3and Ce(Ln)O2(Ln=Sm, Gd, Pr)

We fabricated single cells with a cathode consisting of a LaNi 0.6 Fe 0.4 O₃-Ce 0.8 Sm 0.2 O 1.9 composite (LNF-S20DC composite) active layer and an LNF current collecting layer on a 0.89ZrO₂-0.10Sc₂O₃ -0.01Al₂O₃ electrolyte sheet. The cathode layers were prepared by the screen-printing method. The cathode properties of these cells were measured by the AC impedance method at 800℃. The cathodes with the ceria-LNF composite active layer exhibited high power performance prior to current loading. We investigated the influence of the mixture ratio of LNF and S20DC on the cathodes properties. The Sm in the ceria particles of the composite cathode was substituted with other rare-earth elements. Cathodes with Pr and Gd co-doped ceria in the active layer provided the better performance than those with Sm- or Gd-doped ceria.

Analysis of Electrochemical Performance of SOFCs Using Polarization Modeling and Impedance Measurements

Anode-supported planar solid oxide fuel cells (SOFCs) were fabricated by a single-step cofiring process. It comprised of a porous -stabilized zirconia (YSZ) anode support, a porous and fine-grained anode active layer, a dense YSZ electrolyte, a fine-grained porous Ca-doped composite cathode active layer, and a porous LCM cathode current collector layer. The cell was tested between 700 and with humidified hydrogen (97% ) as the fuel and air as the oxidant. The measured maximum power densities were at , at , and at . The cell was also tested at with various compositions of fuel and oxidant, and the cell parameters, which included the area specific ohmic resistance, exchange current densities, and anodic and cathodic limiting current densities, were obtained through polarization modeling. The polarization resistances of the cell were calculated using the cell parameters obtained from modeling, and compared with the corresponding values measured using impedance spectroscopy. The effect of cell operating conditions on various polarization losses and performance was analyzed in detail using the polarization modeling results.