Research On Preparation And Electrochromic Performance Of Prussian Blue-Based Composite Film

Electrochromic（EC）materials can manifest persistent and reversible optical properties by applying an external voltage or current,which have been widely applied in various applications,such as,energy-saving smart windows,antiglare rear-view mirrors,low power consumption displays and electrochromic iris device.Prussian blue（PB）has been considered as a promising EC material due to high redox reversibility,ease of synthesis,low switch-on voltage and large transmittance,originating from its rigid 3D coordination frameworks.However,PB-based EC films are still subjected to slow switching rate and poor cycle stability.Therefore,in this thesis,the EC performances of Prussian blue were improved by the preparation of composite materials and the design of nanostructures.The pure PB films with different thicknesses were prepared by adjusting the deposition time and the effect of thickness on the electrochromic properties of PB was studied.Finally,the PB films with the thickness of about 195 nm prepared by electrodeposition at the deposition voltage of-0.4 V and deposition time of 70 s exhibit an excellent EC performances.In order to enhance the switching speed of PB films,Pt/Au and Au/PB composite films were constructed by two steps of electrodeposition.The effect of the introduction of Pt and Au metal nanoparticles with high conductivity on the electrochromic properties of PB was investigated,and the charge transfer mechanism of the composite film was studied by the band structure.The introduction of high conductive metal nanoparticles can not only reduce the interfacial contact resistance of the composite film,but also form Schottky junction with PB to accelerate the charge transfer.The results show that the Au/PB film shows a large transmittance modulation range（64.3%at 700 nm）and high coloration efficiency（131.3 cm²/C）.The composite film displays shorter coloration/bleaching switching time（1.36 s/2.32 s）than the PB film（1.92 s/4.08 s）.Additionally,the EC iris devices were designed and assembled using Au/PB film as an EC layer to recede glare phenomena under bright light.The TiO₂/PB nanorods arrays were used as the supporting framework to enhance the binding force between PB and FTO substrate and improve the EC cycle stability.According to the DTF calculation and analysis,the chemical bond between Sn O₂ and TiO₂ is the main reason for the strong binding force between TiO₂ and FTO.The effects of hydrothermal time and concentration of tetrabutyl titanate on the TiO₂nanorods arrays were studied.The results show that the TiO₂ film has the best optical properties when the hydrothermal time is 4 h and the concentration of tetrabutyl titanate is 36.58 mmol/L.The TiO₂ nanorod with strong interaction between TiO₂nanorod and FTO provides robust support for structural integrity.The structure of TiO₂/PB film was not damaged after 50 times peeling with adhesive tape.Benefiting from these effects,the obtained TiO₂/PB composite film shows excellent cycle stability（97.7%transmittance modulation retention after 4000 cycles）.Besides,the two-level EC iris devices were designed to recede glare phenomena under bright light through fast coloring response.The TiO₂/Au/PB terpolymer composite films with ultra-high EC properties were constructed and prepared by hydrothermal and electrodeposition methods.The results show that the introduction of Au nanoparticles can improve the low conductivity of rutile TiO₂ and enhance the conductivity of the film on the basis of ensuring the stability of the structure.Based on these effects,the TiO₂/Au/PB film displays an excellent EC performance with a significant transmittance modulation range（68%at700 nm）,rapid switching speed（1.08 s/2.01 s）,high coloration efficiency（133.4cm²/C）and excellent cycle performance（86.8%after 20000 cycles）.Additionally,the two-level EC iris device with TiO₂/Au/PB EC layer can be applied in smartphones and cameras to shoot clearly strong light sources.