Fabrication of several conducting polymer and metal oxide thin films, and performing the performance tests for electrochromic applications

This study presents a comprehensive overview of the electrochemical synthesis of nanoporous Cu-doped nickel oxide and nanofiber LiClO4 doped PAni thin films on ITO-coated glass substrate. Polyaniline conductive polymer thin films without or with LiClO4 inorganic salt were coated by electrochemical deposition method on ITO surfaces. Electrochromic stability test, electrochemical behavior, coloring performance, optical properties and surface formations of the produced films were studied in detail. The deposited films were found to have a good stability. Electrochemical analyses show that the conductivity of LiClO4 doped PANI film is higher than that of the PANI. Oxidation and reduction peaks, and potentials differ significantly depending on the content of the electrolytes. SEM studies demonstrate that the surface of each film consists of completely nanofibers. Addition of LiClO4 to the deposition electrolyte decreases substantially the diameter of these nanofibers. PANI film with LiClO4 exhibits four colors, while pure PANI film has three different colors. The EDX results obtained from the surface of LiClO4 doped PANI material indicate that PANI and LiClO4 are successfully linked to form PANI/LiClO4 binary thin film. X-ray diffraction analysis and scanning electron microscopy are used to determine the crystal phase and morphology of the NiO and Cu:NiO thin films. The electrochromic behavior of the deposited films is tested by means of cyclic voltammetry, chronocoulometry, repeating chronoamperometry, and electrochemical impedance spectroscopy measurements. The color change from dark brown to transparent appears reversibly well suitable under sequential potential from -0.2 to +1.0 V. After the Cu atoms incorporate into the host NiO matrix, noticeably enhancements are observed in optical modulation (57.1 % at 550 nm), coloration efficiency (13.78 cm2/C) and response time (tb=2.26 s and tc=1.77 s) compared to its as-prepared NiO films. The negative slope of the Mott-Schottky plot shows the films have p-type conductivity, and acceptor density is found as 4.44∙1019 cm-3 and 5.41∙1019 cm-3 for the NiO and Cu:NiO films, respectively. An equivalent electronic circuit is fitted using the measured Nyquist data of the NiO or Cu:NiO semiconductor/electrolyte system. Therefore, the results in this study make a major contribution to the research on energy-saving smart windows by demonstrating analyses in detail.