Electrochromic Devices Based On Conducting Polymers

Eletrochromism refers to a phenomenon that a material changes colors when the material produces reversible redox reaction induced by applied voltage.The device which is assembled by electrochromic materials has broad applications in the construction,automotive,flat panel display,information storage and other fields.Conducting polymers used as electrochromic materials have many advantages,such as simple preparation processes(chemical or electrochemical methods),high-contrast color changes,fast response time and designing molecular structures by "grafting" or "reduction" to meet the need of the color change.In this paper,we mainly applied conducting polymers(polyaniline and poly3-methylthiophene) as electrochromic materials and focused on fabricating a new type of electrochromic devices and improving the performance of electrochromic devices.The work can be divided as follows:1) PANI was prepared by chemical methods.PANI films were prepared by spin-coating;Fabricated P3MeT films by electrochemical methods, characterized morphology of P3MeT films;Made research on the effect of the composition of electrolyte on the electrochromic performce of PANI thin films,preparation of solid polymer electrolyte that can be used in PANI-ECD and P3MeT-ECD.2) Assembling a solid-state vertically configured PANI-ECD, optimizating the electrochromic performance of the device.3) Assembling a solid-state laterally configured PANI-ECD and P3MeT-ECD, study on the electrochromic performance of PANI-ECD and P3MeT-ECD.4) Preparation of PANI films by drop-coating method and fabrication of P3MeT films by electrochemical approach in the same piece of ITO,the assembly of the solid-state laterally configured PANI-P3MeT-ECD device,and the device structure improvement.The main results are summarized as follows:1) By comparing the electrochromic performance of PANI in containing proton acetonitrile electrolyte(0.1 mol L^-1 LiClO₄+0.01 mol L^-1 HClO₄) and non-proton acetonitrile electrolyte(0.1 mol L^-1 LiClO₄),We found that the electrochromic performance of PANI showed more stable in containing proton acetonitrile electrolyte than in non-proton acetonitrile electrolyte.2) A simple solid-state vertically configured PANI-ECD was assembled using PANI as electrochromic layer and the polymer electrolyte(PE: PMMA-PC-EC-LiClO₄ or PE:PMMA-LiClO₄-PC-EC-HClO₄).The device that used containing proton polymer electrolyte(PMMA-LiClO₄-PC-EC-HClO₄) performed better than the one that used non-proton polymer electrolyte (PMMA-LiClO₄-PC-EC),but the cycle stability of the simple solid-state PANI-ECD is not ideal enough.We introduced CeO₂-TiO₂ composite as the complementary electrode of a new solid-state vertically configured PANI-ECD.After optimizing the fabrication process of CeO₂-TiO₂ composite film,the PANI-ECD exhibited reversible electrochromic behavior from yellow at bleached state(-1.5V) to blue at colored state(1.0V.PANI vs.CeO₂-TiO₂) with good cyclie stability.The transmittance of the ECD at 700 nm changed from 42.19%to 13.35% with a coloration efficiency of 152.1cm² C^-1.3) A solid-state laterally configured PANI-ECD was assembled by using PANI as electrochromic layer and the polymer electrolyte (PMMA-LiClO₄-PC-EC-HClO₄).Applied voltages between-0.6V and+0.6V, the device exhibited reversible electrochromic behavior between yellow-green and dark-green.4) A solid-state laterally configured P3MeT-ECD was assembled by using P3MeT as electrochromic layer and the polymer electrolyte (PMMA-LiClO₄-PC-EC-HClO₄).Applied voltages between-1.0V and +1.6V, the device exhibited reversible electrochromic behavior between red and blue.5) The laterally configured P3MeT-PANI-ECD which employed PANI and P3MeT as electrochromic layer,exhibited darkgreen-yellowgreen-blue -red multicolor changes.We also miniaturized electrochromic layer by laser engraving.Introduced CeO₂-TiO₂ as the complementary electrode of PANI-P3MeT,the vertically configured P3MeT-PANI-ECD can show darkgreen-yellowgreen-blue-red multicolor changes,and can show four-color freely.