Preparation And Performance Of Self-Powered Electrochromic Device Based On The Gravure Printed PEDOT:PSS Thin Film

Electrochromic technology refers to a phenomenon that some materials dynamically and reversibly change their optical properties when an external voltage is applied.The working principle of electrochromic device is based on the reversible redox reaction process accompanied by the ion and charge insertion or extraction,which has been widely used in smart windows,low-power optical displays and so on.However,its development remains severely challenging because conventional electrochromic device often needs an external power sources,which not only wastes extra energy but also hinders the independence and portability of the device.In addition,it is noteworthy that the traditional indium tin oxide（ITO）electrode with brittle nature limits its application and development in flexible devices.Herein,to solve the above problems,the fabrication of flexible and lightweight self-powered electrochromic device is of great importance.The main research contents of this thesis are as follows:Due to its low-cost and large-scale,gravure printing is a very promising technique which can be applied in the film-forming of water-soluble electrically conductive polymer poly（3,4-ethylenedioxythiophene）:polystyrene sulfonate（PEDOT:PSS）dispersion with absorbent paper as substrate.Regarding the surface roughness of the paper substrate,different organic solvents were added to the PEDOT:PSS dispersion to enhance its wettability,such as dimethyl sulfoxide（DMSO）,isopropyl alcohol（IPA）or methanol（Me）.Furthermore,the influence of different formic acid processing parameters on the conductivity of paper-based PEDOT:PSS films and the mechanism underlying the conductivity improvement was explored and analyzed.Furthermore,lateral-structure electrochromic devices were assembled using the printed paper-based PEDOT:PSS films.The results showed that formula E:[PEDOT:PSS/DMSO]:IPA=[9.5/5]:1[w/w%],which meets the requirements of uniform film formation on the surface of paper substrate by gravure printing method.Formic acid post-treatment could reduce the sheet resistance of PEDOT:PSS film to 165 Ω sq^-1.The processed film,acting as the functional layer of electrochromic and conductive electrodes at the same time,could be used to produce electrochromic devices with simple structures and excellent color-changing capability.The feasibility of paper-based PEDOT:PSS conductive films in electrode materials and electrochromic materials has been confirmed.Conventional electrochromic devices require an external power source to drive the color change,which causes additional energy consumption.Chemical energy drive is an effective self-energized method for electrochromic devices.Metal foil（Zn,Cu or Al）was used as reduction electrode,PEDOT:PSS film prepared by gravure printing on the surface of paper substrate was used as electrochromic and conductive electrode functional layer to construct a novel selfpowered electrochromic device.The self-coloring effects of electrochromic devices driven by different metal electrodes were compared and analyzed systematically.Furthermore,the working mechanism of self-powered electrochromic devices was explored.The electrochromic properties,electrochemical properties,cyclic stability as well as mechanical flexibility of the devices were characterized and analyzed.The results showed that the paper based self-powered electrochromic device assembled with reducing metal Zn has the highest output voltage（1.31 V）,the best optical contrast（0.34）and the fastest selfcoloring response time（5.2 s）.It also has been featured by energy storage performance(1.38 mAh m^-2 at 0.02 mA cm^-2 current density)and good flexibility.In addition,patterned self-powered electrochromic devices have been successfully fabricated through simple process.Considering the low energy storage performance of Zn-driven electrochromic devices,PEDOT:PSS film prepared on the surface of paper substrate by gravure printing was used as the conductive electrode with PEDOT:PSS deposited on the surface as the positive electrode material,which was employed to explore the influence of the thickness of positive electrode material on the color-changing and energy storage performance of the devices.The same structure devices with ITOglass or PEDOT:PSS-glass as conductive substrate were compared and analyzed.And,the influence of different valence electrolytes also was investigated for the electrochromic devices.The results showed that the self-powered device with three-layer of PEDOT:PSS film as cathnode,and connected with Zn anode through 1 M LiClO₄ aqueous electrolyte,achieved the biggest optical contrast（0.72）,outstanding energy storage performance with discharging capacity of 10.1 mAh m^-2 at 0.02 mA cm^-2,as well as good cycle stability(optical contrast retention 80%after 100 cycles of CA at at 650 nm,capacity retention 95%after 100 cycles of GCD at 0.05 mA cm^-2).The novel paper-based electrochromic energy storage device designed and facribated in this thesis may contribute to the development and application of energy-saving and environment-friendly electrochromic technology.