Optimization of optical and electrochemical properties of PANI, PEDOT conducting polymers to design electrochromic device

Advances in natural sciences and technology dominate creative ideas by giving new pathways for the future aspects of developments in electrochromism. Diving deeper in the materials' molecular structures conceives new problems and opportunities to create valuable information about innovative technologies. Organic materials have promising applications because of their specific properties such as durability, lifetime, low costs, low energy consumption, high ion diffusion, and easy and fast production methods. Therefore, organic materials are used in electrochromic applications to manufacturing functional devices as smart materials. In this project, polymer materials were characterized by CV, CA and impedance spectroscopy methods to use electrochromic applications. PANI and PEDOT materials are mostly used organic substances to develop interesting device prototypes like electrochromic devices, storage devices, and sensors. They were characterized using different methods and experimental results to improve their electrochromic and structural properties. In addition to the improvement process, heat-treatment effect and impedance properties were investigated and equivalent circuit models of developed materials and devices were created using IVIUMSOFT software. Polyaniline comes into prominence by electrochromic properties than other materials. It has three different oxidation states and each state has own color, which is why we used it for electrochromic applications. PANI was synthesized by using different parameters such as an acidic solution, concentration and annealing temperature, voltage ranges, and the scan rate of the voltage. Polyaniline is a unique polymer. It has three oxidation states showing different colors that are yellow, green, blue and their shades that is why polyaniline was chosen for electrochromic applications. It was characterized by electrodeposition and chemical oxidation methods. Electrodeposition method has the capability to polymerize aniline but the strength and lifetime are too low because of adsorption and fast degradation under the room conditions. From this point on, heat treatment was applied to improve electrochemical properties and lifetime of polyaniline films. Advancing in parallel with this process, the chemical oxidation method was carried on to develop polyaniline films. Polyaniline films, which are heat-treated at 90oC, that were coated using the electrodeposition method. They were reached to the better parameters as polyaniline films, which are deposited by chemical oxidation method. Heat-treatment was not applied to polyaniline films developed using chemical oxidation methods because of a quite high lifetime and high adsorption properties. The unique property of chemical oxidation method is that coated films do not require conducting surface in the coating process. Chemical oxidation method was carried on stable room conditions and bath has 15oC using APS as an oxidizing agent. PEDOT films were developed by electrodeposition method onto the ITO surface. 3, 4-ethylenedioxythiophene was used as monomer prepared in acetonitrile/LiClO4 mixing solution. Compensating required ion transportation in the solid electrochromic device is the reason why PEDOT films, the counter electrode, are required to develop. For this respect, optimum parameters found in the experimental processes to polymerize EDOT onto the ITO surface. PEDOT films were found more conducting than PANI films when calculating total charge transportation in chronoamperometry measurement. If these results are taken into consideration, PEDOT films have more conductivity and have more capability for electrochromic application than PANI films. Electrolytes are important materials for electrochromic devices. Characterization of electrochromic films was carried out in solution based 3-probe cell system. PANI film was characterized in acidic media and PEDOT films were characterized in alkaline media. This is the key difference between the two films. Acid includes H+ ions but base that was used for characterization of PEDOT includes Li+ ions. These ions diffuse through the films in electrochemical processes and they show electrochromic properties after diffusion, which causes redox reactions and protonation/deprotonation processes. Gel or solid electrolytes that include ionic structures are used in solid electrochromic devices and they are the basic requirements in a diffusion process to observe electrochromic properties. In PANI/PEDOT solid device application process, durability is controlled in chronoamperometry measurement. It has a very long lifetime, which is higher than ten thousand cycles, but contrast change is quite low due to the transition of color change. The color of the PANI films toggles bleach to green/blue when voltage sweeping negative to positive but PEDOT works inversely. Positive to negative transition could not be observed easily in color change. Nevertheless, it is not the only reason to disparage PANI/PEDOT solid device also electrolyte gel layer is an important parameter for ion transportation between electrodes. It was made of LiClO4 and PMMA mixing structure in PC solution that is well-known electrolyte in such electrochromic applications. Finally, after the investigation of electrolyte for both cell and solid electrochromic devices, optical and electrochemical properties of the optimized organic films were experienced using spectroscopic, cyclic voltammetry and chronoamperometry methods. Then, coloration efficiency, diffusion constants, optical and electrical properties were determined using the required mathematical and physical tools depend on the measurement parameters and results. In the last step, the equivalent circuit model was studied using electrochemical impedance spectroscopy method using obtained data in the measurements. Under the guidance of these results, future applications of studied materials were considered to open a new path for both electrochromism and other potential applications.