PEDOT is a kind of promising intrinsical conductive polymer because of the high chemical and electrochemical stability, low band gap, high conductivity, and excellent transparency in the doped state. It has been investigated in many diverse research fields such as basic polymer science, material science, electrochemistry, electronics and optoelectronics, photovoltaics, corrosion protection, and biosensors. However, the electrochromic devices based on PEDOT exist some drawbacks including low contrast, single color and long response time, which is harmful for practical application. Photonic crystals have drawn a lot of attention due to the possibility to control light propagation. We use silica to assemble the photonic crystals in this paper. Firstly, monodisperse silica particles were prepared by the modified Stöber method, and then the SiO₂ opal film was obtained by a vertical deposition self-assembly method. Then, poly(3,4-ethylenedioxythiophene) (PEDOT) was coated outside the SiO₂ opal template via electrochemical methods, and finally the core-shell structured SiO₂@PEDOT photonic crystal films were obtained. The properties of SiO₂@PEDOT were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), reflection spectra, cycle voltammograms, contrast and response time. The SEM and TEM results show that the SiO₂ microsphere arranged in the form of hexagonal close packing, and the SiO₂@PEDOT has spherical core-shell structure with a rough surface. The diameter of the SiO₂ core is 330 nm, and the thickness of PEDOT shell is about 15 nm. Cycle voltammograms indicate that the electrochemical property of SiO₂@PEDOT film is better than the pure PEDOT film. And the chromatic difference analysis of SiO₂@PEDOT film (28.62) is better than PEDOT film (18.07), too. Through the UV reflectance spectra, contrast and response time measurements, it is found that the color of the SiO₂@PEDOT film is bright and vibrant with a maximal contrast of 39.8%, which is superior to that of the pure PEDOT film (27.4%), and its response speed is also faster. The oxidation time and the reduction time of SiO₂@PEDOT film is 1.3 s and 1.2 s, for PEDOT film, it is 2.0 s and 1.3 s respectively. All the results indicate that it is an effective method to improve the electrochromic properties of conducting polymers by introducing the photonic crystal structures.

Key words: poly(3,4-ethylenedioxythiophene), silica, core-shell structure, photonic crystal, electrochromism