Studies on electrochromic properties of nickel oxide thin films prepared by spray pyrolysis technique

Electrochromic nickel oxide thin films were prepared by using a simple and inexpensive spray pyrolysis technique (SPT) onto fluorine-doped tin oxide (FTO) coated glass substrates from nickel chloride solution. Transparent NiO-thin films were obtained at a substrate temperature 350°C. The films were cubic NiO with preferred orientation in the (1 1 1) direction. Infrared spectroscopy results show presence of free hydroxyl ion and water in nickel oxide thin films. The electrochromic properties of the thin films were studied in an aqueous alkaline electrolyte (0.1 M KOH) using cyclic voltammetry (CV), chronoamperometry (CA) and spectrophotometry. The films exhibit anodic electrochromism, changing colour from transparent to black. The colouration efficiency at 630 nm was calculated to be 37 cm²/C.     

溶胶—凝胶法制备WO_3电致变色薄膜

本文以六氯化钨和乙醇为主要原料, 采用溶胶—凝胶法制备了ＷＯ３ 非晶态电致变色薄膜, 研究了ＷＯ３ 薄膜的结构、化学组成、电致变色性能, 结果表明用该法制备的非晶态ＷＯ３ 薄膜具有良好的电致变色特性     

Sensing properties of organised films based on a bithiophene derivative

Highly reproducible optic and electrochemical sensors have been developed using organised films from a polar bithiophene derivative, the 5-(dimethylamino)-5′-nitro-2,2′-bithiophene (Me₂N–T₂–NO₂). The strength of the molecular dipole moment of this push–pull end-capped bithiophene has permitted to obtain highly ordered, homogeneous and reproducible films by using both the Langmuir–Blodgett and the casting techniques. The organisation of the molecules in LB films and cast films has been established by means of UV–vis, infrared and Raman spectroscopy and by AFM.Me₂N–T₂–NO₂ thin films possess appealing optical and electrochemical sensing capabilities. UV–vis spectra can be modified in the presence of a variety of volatile organic compounds and the sensitivity is related to the polarity of the gas analysed. Films can also be used as electrochemical sensors because the characteristics of the current/potential curves are sensitive to the nature of the electrolytic solution. The spectral changes accompanying the applied voltage could be used to produce ionochromic sensor electrodes.The structure of the films has an important impact in the sensing properties of the films and in their stability. The optical and electrochemical sensing properties of Langmuir–Blodgett films are more reproducible than those observed in cast films. This makes films prepared using the LB technique to be preferred as sensing devices. However the casting technique provides a fast method to obtain cheap and highly ordered sensors.     

Electrochemically-switchable emission and absorption by using luminescent Lanthanide(III) complex and electrochromic molecule toward novel display device with dual emissive and reflective mode

Electroswitching of emission and coloration was achieved by a combination of a luminescent Eu(III) complex and an electrochromic molecule of diheptyl viologen (HV²⁺), indicating that the complex-molecule combination could be used as a display material with dual emissive and reflective modes. The coloration of the material was associated with the electrochromism of HV²⁺. Emission control was found to be possible due to the electrochromism of HV²⁺ via intermolecular energy transfer from the excited state of the Eu(III) ion to the reduced state of HV⁺. By using this mechanism, dual emissive and reflective representation of numerical characters were demonstrated.     

Optical, electrochemical and electrogravimetric behavior of poly(1-methoxy-4-(2-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) films

Poly(1-methoxy-4-(2-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) films spin-cast from chloroform solution were characterized by cyclic voltammetry, in situ spectroelectrochemistry, and electrochemical quartz crystal microbalance (EQCM) measurements. The MEH-PPV films exhibited two well-defined redox waves during p- and n-electrochemical doping, and a mass gain at the end of each cycle that is characteristic of the movement of ions and solvent into and out the film. The electronic energy gap of MEH-PPV was estimated as 2.35 eV from the anodic and cathodic onset potentials obtained by cyclic voltammetry, in good agreement with the value of optical energy gap determined from the absorption edge, 2.21 eV. The films also showed a reversible and stable electrochromic transition at a positive range of applied potentials from reddish-orange (neutral form) to brownish-green (oxidized form).     

Optical properties of electrochromic iridium oxide and iridium-tantalum oxide thin films in different colouration states

Electrochromic iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films were prepared by sputtering. Complex refractive indices were determined for samples deposited on indium-tin oxide covered glass in different colouration states, and for as-deposited samples on sapphire and Corning glass. The refractive index was found to be practically constant for both IrOx (∼1.3) and IrTaOx (∼2). The extinction coefficient was found to vary between the coloured and bleached states with ∼35% for IrOx and ∼55% for IrTaOx at 660 nm. This is believed to be a result of the removal of intraband transitions within the Ir t_2g band during bleaching.     

Nickel oxide sol-gel films from nickel diacetate for electrochromic applications

Nickel diacetate tetrahydrate, [Ni(acetate)₂·4H₂O] and nickel diacetate dimethylaminoethanol, [Ni(acetate)₂(dmaeH)₂] were successfully used to deposit NiO_x thin films on conductive glass substrates by sol-gel techniques for large area electrochromic applications. Homogeneous one layer films 100 nm thick were deposited by spin coating 0.5 M [Ni(acetate)₂·4H₂O] in dmaeH at 1000 rpm and by dip coating methods. The NiO_x films were characterised by X-ray diffraction, transmission electron microscopy and atomic force microscopy. The thin film electrochromic performances were characterised by means of optical (transmittance) and electrochemical (cyclic voltammetry) methods. On early cycling NiO_x thin films present an activation period, related to an increase in capacity. The electro-optical data show an increase in the electrochromic response (i.e. an increase in contrast and colouration efficiency) upon cycling. Following this initial activation period a steady state is reached in which the thin films reversibly switch from transparent to brown. The anodically coloured NiO_x thin films are therefore suitable for use in a complete electrochromic cell with tungsten oxide as the cathodic colouring layer. However, the films are not fully stable with long cycling.     

Multichromic conducting copolymer of 1-benzyl-2,5-di(thiophen-2-yl)-1H-pyrrole with EDOT

Despite the significant progress made in the field of electrochromic polymers, the multichromic facility of current knowledge is restricted. Therefore, as previously proven, electrochemical copolymerization of 1-benzyl-2,5-di(thiophen-2-yl)-1H-pyrrole (SNBS) and 3,4-ethylenedioxythiophene (EDOT) was used as a strategy to achieve desired multichromic properties, where the resultant copolymer displayed distinct color changes between claret red, yellow, green, and blue colors with short switching times and high optical contrast. As an application, absorption/transmission type electrochromic device with indium tin oxide (ITO)/copolymer/gel electrolyte PEDOT/ITO configuration was constructed, where copolymer and PEDOT functioned as the anodically and the cathodically coloring layers, respectively. Results implied the successive use of this copolymer in electrochromic device applications, since the device exhibited short switching times with a wide color variation upon applied potential.     

Electrochromic properties of heat-treated thin films of CeO2–TiO2–ZrO2 prepared by sol–gel route

CeO₂–TiO₂–ZrO₂ thin films were prepared using the sol–gel process and deposited on glass and ITO-coated glass substrates via dip-coating technique. The samples were heat treated between 100 and 500 °C. The heat treatment effects on the electrochromic performances of the films were determined by means of cyclic voltammetry measurements. The structural behavior of the film was characterized by atomic force microscopy and X-ray diffraction. Refractive index, extinction coefficient, and thickness of the films were determined in the 350–1000 nm wavelength, using nkd spectrophotometry analysis.Heat treatment temperature affects the electrochromic, optical, and structural properties of the film. The charge density of the samples increased from 8.8 to 14.8 mC/cm², with increasing heat-treatment temperatures from 100 to 500 °C. It was determined that the highest ratio between anodic and cathodic charge takes place with increase of temperature up to 500 °C.     

Thickness-dependent electrochromic properties of solution thermolyzed tungsten oxide thin films

Tungsten oxide (WO₃) thin films are prepared by using a simple and inexpensive solution thermolysis technique. Thin film samples of different thickness are obtained by varying quantity of ammonium tungstate solution sprayed onto the preheated conducting glass substrate. A simple three-electrode cell has been formed to study the electrochemical and electrochromic properties. The electrochemical parameters of the cell such as anodic peak current, anodic peak potential, threshold voltage, amount of H⁺ ions intercalated into and deintercalated out of the WO₃ samples are calculated. The effect of film thickness on these parameters are studied. The extent of electrochromism and reversibility of the colouration/bleaching processes of various WO₃ samples are described. The colouration efficiencies at 633 nm are calculated. The maximum colouration efficiency obtained for thicker film, is 56 cm²/C. The samples were found to be stable in 0.05N H₂SO₄ electrolyte up to 1×10³ colour/bleach cycles.