The effect of various concentrations of PVDF-HFP polymer gel electrolyte for dye-sensitized solar cell

A PVDF-HFP gel electrolytes based DSSCs were fabricated successfully, where gel electrolytes with 2.5 wt.%, 5 wt.%, 10 wt.% and 15 wt.% PVDF-HFP are included, respectively. Linear sweep voltammetry (LSV), photocurrent–voltage measurements and electrochemical impedance spectra (EIS) were measured. As the results shown, the apparent diffusion coefficient (D_app) of I⁻ and I₃⁻ decreased as PVDF-HFP increased. D_app of I⁻ and I₃⁻ are decreased from 1.87 × 10^− 6 to 0.67 × 10^− 6 cm²/s and 3.28 × 10^− 6 to 0.88 × 10^− 6 cm²/s, respectively. For the solar cell measurements, the short circuit current density (J_sc) were affected by the ion motilities, which was decreased from 11.58 mA/cm² to 8.17 mA/cm², and the energy converting efficiency (η %) was decreased from 5.17% to 2.79%. For electrochemical impedance spectra (EIS) measurements, the ionic diffusion impedance for the redox-couple (I⁻/I₃⁻) in the gel electrolyte was also increased with the concentration of PVDF-HFP from 0.61 Ω to 8.17 Ω. In the Bode Plots, the electron lifetime (τ_e) of the 2.5 wt.% and 5 wt.% PVDF-HFP electrolytes was increased from 40.52 ms to 48.48 ms and 41.29 ms, respectively. However, τ_e was decreased in the concentrations of 10 wt.% and 15 wt.% PVDF-HFP, due to the ion motilities that were decreased by excessing PVDF-HFP polymer. For gel electrolyte, the cell of 2.5 wt.% PVDF-HFP exhibited a better J_SC of 10.89 mA/cm², a higher energy conversion efficiency (η) of 4.75%, a higher fill factor (FF) of 61.26%, and a smaller R of 1.06 Ω than the 15 wt.% PVDF-HFP based cell.     

Fluorosilicate and fluorophosphate superfluorescent multicore optical fibers co-doped with Nd3+/Yb3+

In the paper spectroscopic properties of two fluorosilicate and fluorophosphate glass systems co-doped with Nd³⁺/Yb³⁺ ions are investigated. As a result of optical excitation at the wavelength of 808 nm strong and wide emission in the 1 μm region corresponding to the superposition of optical transitions ⁴F_3/2 → ⁴I_11/2 (Nd³⁺) and ²F_5/2 → ²F_7/2 (Yb³⁺) can be observed. The optimization of Nd³⁺ → Yb³⁺ energy transfer in both glasses allows to manufacture multicore optical fibers with narrowing and red-shifting of amplified spontaneous emission (ASE) at 1.1 μm.     

Improvement of 1.53 μm emission and energy transfer of Yb3+/Er3+ co-doped tellurite glass and fiber

To improve the 1.53 μm band emission of Er³⁺, the trivalent Yb³⁺ ions were introduced into the Er³⁺ single-doped tellurite glass with composition of TeO₂–ZnO–La₂O₃, a potential gain medium for Er³⁺-doped fiber amplifier (EDFA). The improved effects were investigated from the measured 1.53 μm band and visible band spontaneous emission spectra together with the calculated 1.53 μm band stimulated emission (signal gain) spectra under the excitation of 975 nm laser diode (LD). It was found that Yb³⁺/Er³⁺ co-doping scheme can remarkably improve the visible band up-conversion and the 1.53 μm band fluorescence emission intensity, and meanwhile improves the 1.53 μm band signal gain to some extent, which were attributed to the result of the effective energy transfer of Yb³⁺:²F_5/2 + Er³⁺:⁴I_15/2 → Yb³⁺:²F_7/2 + Er³⁺:⁴I_11/2. The quantitative study of energy transfer mechanism was performed and microscopic energy transfer parameters between the doped rare-earth ions were determined. In addition, the spectroscopic properties of Er³⁺ were also investigated from the measured absorption spectrum according to the Judd–Ofelt theory, and the structure behavior and thermal stability of the prepared tellurite glass were analyzed based on the X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurements, respectively.     

Effect of different ethanol/water solvent ratios on the morphology of SnO2 nanocrystals and their electrochemical properties

We report on the effect of different ethanol/water solvent ratios on the morphology of SnO₂ nanocrystals prepared by the conventional hydrothermal method and their electrochemical properties. The nanocrystals were structurally and morphologically characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), surface area measurements, and transmission electron microscopy. The XRD patterns indicate that the sphere-like SnO₂ microcrystals have a rutile-type tetragonal structure and FESEM images show that the microspheres have a diameter of 2–5 μm. We found that the ethanol/water volume ratio plays an important role in formation of the final product. Electrochemical tests revealed that the SnO₂ microspheres had a high initial capacity of 1546 mAh g^?1 at a current density of 100 mA g^?1 and retained a reversible capacity of 439 mAh g^?1 after 30 discharge cycles.     

Effect of aqueous electrolyte on pseudocapacitive behavior of chemically synthesized La2S3 electrode

Lanthanum sulfide electrode (La₂S₃) is prepared by a low cost, simple and room temperature chemical route for energy storage. The surface morphology of La₂S₃ film is revealed through field emission scanning electron microscopy. For the energy storage purpose, the pseudocapacitive behavior of La₂S₃ electrode is studied in 1 M aqueous Na₂SO₄ and 1 M KOH electrolytes. La₂S₃ electrode achieved maximum specific capacitance of 358 F g⁻¹ at 5 mV s⁻¹ scan rate with 78% electrochemical cyclic stability over 1000 cycles in 1 M Na₂SO₄ electrolyte. The galvanostatic charge–discharge study demonstrated the energy density of 35 Wh kg⁻¹ at power density of 1.26 kW kg⁻¹. The electrochemical impedance study showed field assisted charge transfer process with relaxation time of 32 ms in 1 M Na₂SO₄ electrolyte ensuring fast redox reaction.     

Photocatalytic degradation of methyl orange and gas-sensing performance of nanosized ZnO

ZnO nanoparticles were synthesized by calcining composites of zinc nitrate and poly(vinyl pyrrolidone) (PVP, molecular weight 30 000) at a mass ratio of 1:2 at 500 °C for 2 h. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to characterize the as-synthesized ZnO nanoparticles. The particles ranged in size from 30 to 50 nm. Infrared spectra of PVP and the PVP+Zn(NO₃)₂·6H₂O composite revealed coordination between the carbonyl (C=O) of PVP and Zn²⁺ of zinc nitrate, which led to a uniform nanoparticle morphology. The gas-sensing properties and photocatalytic performance of the final product were systematically investigated. The results show that the ZnO nanoparticles exhibit both a high response for ethanol detection and excellent photocatalytic activity for degradation of methyl orange under UV irradiation for 30 min.     

Electrochemical growth of tin(II) oxide films: Application in photocatalytic degradation of methylene blue

We have investigated the semiconducting and photoelectrochemical properties of SnO films grown potentiostatically on tin substrate. The oxide is characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The anodic process corresponds to the formation of SnO·nH₂O pre-passive layer that is removed upon increasing potential due to surface etching at the metal/oxide interface. SnO films deposited for long durations (>50 mn) are uniform and well adhered; they thicken up to ~50 nm by diffusion-controlled process and the growth follows a direct logarithmic law. The thickness is determined by coulometry and the X-ray diffraction indicates the tetragonal SnO phase (SG: P4/mmm) with a crystallite size of 32 nm. The Mott–Schottky plot is characteristic of n type conductivity with an electrons density of 5.72×10¹⁸ cm⁻³, a flat band potential of −0.09 V_SCE and a depletion width of ~10 nm. The valence band, located at 5.91 eV below, vacuum is made up of hybridized O²⁻:2p Sn²⁺:5s while the conduction band (4.45 eV) derives from Sn²⁺:5p orbital. The electrochemical impedance spectroscopy (EIS) measured in the range (10⁻²–10⁵ Hz) shows the contribution of the bulk and grain boundaries. The energy band diagram predicts the photodegradation of methylene blue on SnO films. 67% of the initial concentration (10 mg L⁻¹) disappears after 3 h of exposure to visible light (9 mW cm⁻²) with a quantum yield of 0.072.     

Red luminescence of spherical CuxZn1−xS semiconductor nanoparticles using 2-mercaptoethanol as capping agent

Cu²⁺-doped (0–2 at%) ZnS nanoparticles stabilized by 2-mercaptoethanol (2-ME) were successfully prepared using wet precipitation route in aqueous solution. The structural and optical characteristics were studied by various techniques. XRD pattern showed zinc blende cubic structure of Cu²⁺-doped ZnS with grain size of 4±0.5 nm. Spherical shape and well distribution of particles is confirmed by TEM, SEM and STM microscopy. Copper doping were identified by elemental dispersive (EDS) spectrometry. UV–vis spectroscopy revealed strong confinement effect due to blue shift in absorption shoulder peak as compared to bulk ZnS. Red luminescence band at～657 nm on Cu²⁺ doping may be arising from recombination of electrons at sulfur vacancies (V_s) and Cu(t₂) states formed at ZnS band gap. Optimum concentration of 0.25 at% (red band) of Cu²⁺ doping was selected by the observed enhanced PL emission.     

Improved performance of nanoporous TiO2 film in dye-sensitized solar cells via ZrCl4 and TiCl4 surface co-modifications

In this study, nanoporous TiO₂ films were modified by a dip-coating process using a mixture aqueous solution of ZrCl₄ and TiCl₄ followed by calcination to prepare a photoanode for dye-sensitized solar cells. Compared with the control film modified with 0.04 mol L⁻¹ TiCl₄, the power conversion efficiency of the TiO₂ film modified with a mixed solution of 0.05 mol L⁻¹ ZrCl₄ and 0.04 mol L⁻¹ TiCl₄, was 18.67% higher because of the improved short circuit current (J_sc) and open circuit voltage (V_oc). The improvement in J_sc was due to the suppression of charge recombination, which was demonstrated by a series of measurements, including electrochemical impedance spectroscopy, monochromatic incident photon-to-electron conversion efficiency spectroscopy, and the open-circuit voltage decay technique. The Mott-Schottky measurement results indicated that the negative shift of a flat band led to the increased V_oc.     

Enhanced field emission and hysteresis characteristics of aligned carbon nanotubes with Ti decoration

The field emission behavior of aligned carbon nanotubes (CNTs) is remarkably improved by decorating their surfaces with Ti nanoparticles through a sputtering process. The CNT/Ti(4 nm) sample shows a low turn-on field of 0.63 V/μm at 10 μA/cm², low threshold field of 1.06 V/μm at 1 mA/cm², and maximum field emission current density of 23 mA/cm² at 1.80 V/μm. The enhanced field emission properties of the CNT/Ti samples are attributed to the added defect sites and Ti nanoparticles, which increase the field enhancement factor and density of emission sites. Stability measurements indicate that the Ti coating, which acts as a protective layer, also strengthens the field emission stability of the CNT arrays. Moreover, the extent of hysteresis in the current–voltage sweep highly depends on the voltage-sweep speed.     

High-performance barrier using a dual-layer inorganic/organic hybrid thin-film encapsulation for organic light-emitting diodes

We report an inorganic/organic hybrid barrier that combines the alternating deposition of a layer of ZrO₂ using low temperature atomic layer deposition and a 16-μm-thick layer of UV-curable NOA63 epoxy using spin-coating. The effective water vapor transmission rates of single ZrO₂ film was improved by adding solution epoxy from 3.03 × 10⁻³ g/m² day to 1.27 × 10⁻⁴ g/m² day in the hybrid NOA63/ZrO₂/NOA63/ZrO₂ films at 20 °C and a relative humidity of 60%. In consequence, the organic light-emitting diodes encapsulated with inorganic/organic hybrid barriers were undamaged by environmental oxygen and moisture and their luminance decay time improved by a considerable extent.     

Synthesis of samarium telluride thin films by successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application

The present paper deals with synthesis of samarium telluride (Sm₂Te₃) thin films using simple and low cost successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application. The Sm₂Te₃ thin films are characterized by X-ray diffraction (XRD) for structural determination, energy dispersive analysis of X-ray (EDAX) for elemental composition, field emission scanning electron microscopy (FE-SEM) for surface morphological study and contact angle measurement for wettability study. The Sm₂Te₃ exhibits orthorhombic crystal structure with cloud like surface morphology. The film surface showed lyophilic behavior with contact angle of 5.7° for propylene carbonate (PC). Further, electrochemical measurements are carried out in LiClO₄–PC electrolyte using cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS) techniques. The Sm₂Te₃ film showed maximum specific capacitance and energy density of 144 F g⁻¹ and 10 W h kg⁻¹ respectively. The EIS study showed negligible change in resistive parameters after 1000 electrochemical cycles.     

Characterization of CoxNiyO hybrid metal oxide nanoparticles as charge trapping nodes in nonvolatile memory devices

The Co_xNi_yO hybrid metal oxide nanoparticles (HMONs) embedded in the HfO_xN_y high-k dielectric as charge trapping nodes of the nonvolatile memory devices have been formed via the chemical vapor deposition using the Co/Ni acetate calcined and reduced in the Ar/NH₃ ambient. A charge trap density of 8.96 × 10¹¹ cm^?2 and a flatband voltage shift of 500 mV were estimated by the appearance of the hysteresis in the capacitance–voltage (C–V) measurements during the ±5 V sweep. Scanning electron microscopy image displays that the Co_xNi_yO HMONs with a diameter of ～10–20 nm and a surface density of ～1 × 10¹⁰ cm^?2 were obtained. The mechanism related to the writing characteristics are mainly resulted from the holes trapping. Compared with those devices with the Co_xNi_yO HMONs formed by the dip-coated technique, memory devices with the Co_xNi_yO HMONs fabricated by the drop-coated technique show improved surface properties between the Co_xNi_yO HMONs and the HfON as well as electrical characteristics.     

Multilevel characteristics and operating mechanisms of nonvolatile memory devices based on a floating gate of graphene oxide sheets sandwiched between two polystyrene layers

Nonvolatile organic memory devices were fabricated utilizing a graphene oxide (GO) layer embedded between two polystyrene (PS) layers. Scanning electron microscope images of GO sheets sandwiched between two PS layers showed that the GO sheets were clearly embedded in the PS layers. Capacitance–voltage (C–V) curves of the Al/PS/GO/PS/n-type Si devices clearly showed hysteresis behaviors with multilevel characteristics. The window margin of the nonvolatile memory devices increased from 1 to 7 V with increasing applied sweep voltages from 6 to 32 V. The cycling retention of the ON/OFF switching for the devices was measured by applying voltages between +15 and −15 V. While the capacitance of the memory devices at an ON state have retained as 230 pF up to 10⁴ cycles, that at an OFF state maintained as 16 pF during three times of repeated measurements. The extrapolation of the retention data for the devices maintained up to 10⁶ cycles. The operating mechanisms of the nonvolatile organic memory devices with a floating gate were described by the C–V results and the energy band diagrams.     

Synthesis,characterization, and supercapacitor studies of manganese (IV) oxide nanowires

One-dimensional manganese (IV) oxide (MnO₂) (～20 nm in average diameter) were synthesized by cathodic electrodeposition and heat treatment. The mechanism of electrodeposition and nanowire formation were discussed. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR). Nanowires with varying lengths and diameters were found in TEM and SEM images of the sample. The results of N₂ adsorption–desorption analysis indicated that the BET surface area of the MnO₂ nanowires was 157 m² g^?1 and the pore size distributions were 2.5 and 4.5 nm. The electrochemical performances of the prepared MnO₂ as an electrode material for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements in a solution of 0.5 M Na₂SO₄. The higher specific capacitance of 318 F g^?1 and good capacity retention of 86% were achieved after 1000 charge–discharge cycles had been observed for the MnO₂ nanowires electrode.     

Vertically aligned ZnO nanowires prepared by thermal oxidation of RF magnetron sputtered metallic zinc films

ZnO nanowires have been successfully grown by thermal oxidation of metallic zinc films at 430 °C. Polycrystalline zinc films were deposited on Si (100) substrates by RF magnetron sputtering utilizing discharge power from 70 to 180 W. Experimental results show that 70 W discharge power results in the formation of porous zinc nanoparticles that prevent zinc atom from diffusion and thus does not result in the formation of ZnO nanowires by subsequent thermal oxidation. By increasing discharge power to 120 W the zinc film transforms to Zone II with a columnar structure, while further increase in discharge power to 180 W results in re-crystallization and formation of micron-sized hexagonal structures on the surface. Vertically aligned ZnO nanowires can only be obtained by thermal oxidation of columnar zinc films that exhibit a field emission threshold of 5.3 V/μm (at a current density of 10 μA/cm²) with a field enhancement factor of 1834. A target current density of 0.75 mA/cm² is achieved with a bias field less than 10 V/μm.     

Carbazole based A-π-D-π-A dyes with double electron acceptor for dye-sensitized solar cell

Three novel carbazole-based A-π-D-π-A-featured dyes (CSG1–CSG3) have been designed, synthesized for applications in dye-sensitized solar cells and fully characterized with NMR, MS, IR, UV–vis and electrochemical measurements. These dyes share the same donor (N-hexylcarbazole) and acceptor/anchoring group (cyanoacrylic acid), but differs in conjugated linkers incorporated, such as benzene, furan or thiophene, to configure the novel A-π-D-π-A framework for effective electron flow. The power conversion efficiencies were observed to be sensitive to the π-bridging linker moiety. The photovoltaic experiments showed that dye with a benzene linker exhibited a higher open-circuit voltage (0.699 V) compared to thiophene and furan linker. Among all dyes, CSG2 containing a thiophene linker exhibited the maximum overall conversion efficiency of 3.8% (J_SC = 8.90 mA cm⁻², V_OC = 584 mV, FF = 0.74) under standard global AM 1.5 G solar condition. Under similar fabrication conditions, champion dye N719 exhibited the maximum overall conversion efficiency of 6.4% (J_SC = 14.74 mA cm⁻², V_OC = 606 mV, FF = 0.716).     

Solid-state sensing tip for zinc ion with double parallel optical fibers embedded in fluorescent hydrogel

A tip-shaped zinc ion solid-state sensor is made by two parallel optical fibers embedded closely in a sensing hydrogel film. The film is made of poly(2-hydroxyethyl methacrylate) (poly HEMA)hydrogel mixed with the selective fluorescent probe meso-2,6-Dichlorophenyltripyrrinone (TPN-Cl₂) with weight ratio of 0.025 wt%. A 405 nm laser output is sent from one fiber and the 622 nm fluorescence of the doped hydrogel is collected by the second fiber. Each fiber diameter is 370 μm (core is 300 μm), whose sum is roughly the tip diameter. The 0.4 cm by 0.5 cm tip has real-time response for zinc ion concentration over 10⁻⁶ M, with marginal signal for 10⁻⁷ M. The tip is inserted inside an oyster and successfully detects the zinc ions, showing that the sensor works in complex body fluid and tolerates certain mechanical stress. To show the potential application for medicine, the sensing film is applied for primary neuronal cultures. We report for the first time zinc ions release at concentration levels 10⁻⁶–10⁻⁷ M to the medium under stress conditions of ischemia, inflammation, and intoxication. Furthermore, this correlates with the zinc levels detected by biochemical assay. Such sensing tip has great potential for biomedical monitoring ex vivo or in vivo.     

Synthesis and semiconducting properties of Na2MnPO4F. Application to degradation of Rhodamine B under UV-light

Na₂MnPO₄F is synthesized by hydrothermal route at 453 K and the physical properties and photo-electrochemical characterizations are reported. The compound crystallizes in a monoclinic system (SG: P 2₁/n) with the lattice constants: a=13.7132 Å, b=5.3461 Å, c=13.7079 Å, β=119.97°. The UV–visible spectroscopy shows an indirect optical transition at 2.68 eV; a further direct transition occurs at 3.70 eV, due to the charge transfer O²⁻: 2p → Mn²⁺: e_g. The thermal variation of the electrical conductivity is characteristic of a semiconducting behavior with activation energy of 39 meV and an electron mobility (µ_318 K=5.56×10⁻⁴ cm² V⁻¹ s⁻¹), thermally activated. The flat band potential (+0.47 V_SCE) indicates that the valence band derives mainly from O²⁻: 2p orbital with a small admixture of F⁻ character while the conduction band is made up of Mn²⁺: t_2g orbital. The electrochemical impedance spectroscopy shows the contribution of both the bulk and grains boundaries. The photocatalytic performance of Na₂MnPO₄F for the degradation of Rhodamine B (RhB) is demonstrated on the basis of the energy diagram. 88% of the initial concentration is degraded under UV light and the oxidation follows a first order kinetic with a rate constant of 0.516 h⁻¹. Neither adsorption nor photolysis is observed. The photoactivity results from the electron transition from the hybridized band (O²⁻, F⁻) to the Mn²⁺: e_g orbital, occurring in the UV region. The catalyst was subjected to three successive photocatalytic cycles, thus proving its long term stability.     

Heterostructure of CdO-ZnO nanoparticles intercalated on PANI matrix for better thermal and electrochemical performance

New heterostructure of CdO-ZnO nanoparticles intercalated on PANI matrix (CZP) have been synthesized by two step solution route: firstly, CdO-ZnO heterostructure was prepared by the simple chemical precipitation method and the resulting materials are effectively coupled on PANI by the chemical oxidative polymerization method in acidic medium using APS as oxidant. The resulting respective hybrid materials of CdO, ZnO and PANI matrix were characterized and confirmed (functional groups and crystalline nature) by FTIR, RAMAN and XRD analysis. From the HR-SEM analysis, hybrid materials of CdO-ZnO/PANI matrix has agglomerated hexagonal structure was derived from the granular structure of PANI. Thermo gravimetric analysis showed that CZP hybrid composite has higher thermal stability than ZnO-PANI and PANI matrix. Surface area and pore volume of the hybrid heterostructure obtained to be 54.52 m²/g and 0.14 cm³/g respectively. The electrical properties of CdO-ZnO particles intercalated on PANI matrix are evaluated in three different electrolyte solutions. In the sense, 1 M H₂SO₄ electrolyte solution exhibits better current response than the other electrolyte solution. From the results shows that the hybrid hetero structure of (CZP) exhibited better thermal and electrochemical performances than ZnO-PANI hybrid and the capacitance retention showing 72.6% after 500 cycles at a current density of 0.5 mA g⁻¹, thus the electrode materials possess good specific capacitance and cycle stability. Hence the CZP is a promising material in the field of super capacitor applications.