Influence of Different Substrates on the Electrochromic Property of Polyaniline Films

The polyaniline （PANI） films doped with complex acid （sulfuric acid and sulfosalicylic acid） were prepared using the potentiostatic method on bare nickel flake （NF） and flexible polyethylene terephthalate （PET）/indium tin oxide （ITO） substrates. The contents of the PANI films,surface elements, electrochromic property and electrical conductivity were characterized by energy dispersive X-ray spectrometer （EDS）, cyclic voltammetry （CV） and electrochemical impedance spectroscopy （EIS）. The experimental results show that differences exist among cycle stability, redox reversibility and response time of polyaniline films on these two kinds of substrates, but the electrochromic phenomenon of the PANI films is in substantial agreement. The equilibrium transmittance spectra in the visible region （400-800 nm） for the PANI film on flexible PET/ITO substrate was obtained at different applied potential from -0.4 to 1.5 V. The results show that the transmittance of the PANI film by applying voltage is adjustable in a row and has excellent electrochromic performance.

Characterization of Electrochromic Properties of Polyaniline Thin Films Electropolymerized in H2SO4 Solution

Polyaniline (PANI) onto indium-doped tin-oxide (ITO)-coated glass samples were prepared by electroopolymerization in 0.5 M H2SO4 solution. Structure and morphology characterization of the PANI films demonstrated that the films were grown onto ITO substrates in the form of polycrystalline microbelts separated by micropores. By analysing the UV-Vis absorption spectra of the PANI films, the energy bandgap was found to be approximately 2.75 eV. The PANI/ITO films exhibited a good reversible electrochromic display (ECD) performance when cycled in 0.1 M LiClO4 + pro-pylene carbonate. The response time of the ECD coloration was found to be as small as 15 s and the coloration efficiency was found to be 8.85 cm2 C-1. After 100 cycles of the ECD performance, the cyclic voltammetry curve of the working electrode maintained unchanged. This demonstrates that the electropolymerized PANI films can be served as a good candidate for ECD applications, taking advantage of their excellent properties in terms of chemical stability.

The Effect of Cd on the Electrochromic Properties of NiO_xH_y film

The effects of 2.8% Cd on the electrochromic properties of NiOxHy film were studied. The film was electrodeposited on both the polished Ni plate and conductive ITO glass to study its electrochemical and optical characteristics respectively. It was found that Cd could decrease the working voltage and increase the oxygen evolution voltage as well as the transmittance difference of colored and breached states of the film. However, it has little effect on the kinetic process.

Low Band Gap Polymers Synthesized by Electrochemical Polymerization for Electrochromic Devices

Two novel monomers, 10,13-bis（4-octyl-2-thienyl）-dibenzo[a,c]phenazine （OTBP） and 10,13-bis（4-octyl-2- thienyl）-dipyrido[3,2-a：2＇,3＇-c]phenazine （OTPP）, were synthesized. Electrochemical polymerization of OTPP and OTBP were carried out in acetonitrile/dichloromethane （ACN/DCM） solvent mixture containing tetra-n- butylammoniumhexafluorophosphate （TBAPF6）, and electrochromic properties of POTPP and POTBP are described. Furthermore, the effects of structural difference on electronic properties of electron acceptor units, electrochemical and electrochromic properties of two resulting polymers were examined. The results showed that the OTBP was polymerized at lower potential than OTPP, and this is because OTPP contains two more N atoms in electron acceptor unit and its electron withdrawing ability is stronger than that of OTBP. The UV-Vis-NIR spectra analysis revealed that the POTPP film has three absorption bands centered at 570 nm, 925 nm and 1581 nm, and the POTBP film has two absorptions at 566 nm and 1009 nm, respectively. The electrochromic properties indicated that the two polymer films exhibits reasonable optical contrasts and response time with low band gaps, defined as the onset of the absorption band at 570 nm for POTPP and the absorption band at 566 nm for POTBP, as 1.74 eV for POTPP and as 1.69 eV for POTBP.

Preparation and electrochromism of pyrochlore-type tungsten oxide film

Pyrochlore-type WO3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid, from which films were made by dip coating process with indium-tin oxide （ITO）. The obtained films were characterized by thermogravimetric and differential thermal analysis （TG-DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, cyclic voltammetry （CV）, chronoamperometry （CA） and ultraviolet- visible （UV-Vis） absorption. Results show that the crystal of the pyrochlore-type WO3 powder is perfect. When the calcination temperature rises from room temperature to 500℃, the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase, finally it will completely convert to WO3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300℃ exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm^2-C^-1 at 884 nm.