Controllable Construction And Performance Of Polythiophene-based Complementary Electrochromic Devices

The application of polythiophene-based electrochromic materials in electrochromic device(ECDs)is limited due to their poor cycle stability and long response time.When the counter electrode(ion storage layer)of ECDs is also composed of an electrochromic film,the assembled device is called a complementary ECD.Compared with ECDs with a single electrochromic film,the complementary ECDs have more excellent cycle stability,higher optical contrast and coloration efficiency.Among them,the thickness of ion storage layer,the performance optimization of transparent conductive substrate,and the morphology control of electrochromic layer are key factors that determine the performance of complementary ECDs.In this paper,we assembled the complementary ECDs using P3 TE,PT32BT,and P3 DT films as electrochromic layers and PEDOT films as ion storage layers,respectively.The effects of adjusting the thickness of ion storage layer,modifying the ITO substrate,and changing the film electrodeposition method on the electrochromic performance of polythiophene-based ECDs were investigated.(1)P3TE and PEDOT thin films were prepared on ITO electrodes using pulsed electrodeposition(PED)and potentiostatic deposition(PSD)methods,respectively,and assembled into the complementary ECDs.The thickness of PEDOT films is changed by adjusting the electrodeposition time.The optimal matching thickness between the ion storage layer and P3 TE electrochromic layer is explored,and the mechanism of influence of ion storage layer thickness on the electrochromic performance of ECDs is revealed.It was found that the nanoparticle distribution of PEDOT-5 film was the most uniform,and its particle size was smaller.Compared with PEDOT-10 and PEDOT-15 films,the surface of PEDOT-5 film was rougher,more loose,and had a larger specific surface area.The nanostructured morphology of PEDOT-5 film was most conducive to electron transport,ion diffusion and migration,resulting in better cycle stability(after 180 cycles,there was almost no attenuation of optical contrast)and shorter response time(its coloration time and bleaching time were 2.28 and 0.41 s,respectively)for ECD-5.(2)A layer of H-MWCNTs was prepared on the surface of ITO glass by spray-coating method,and then a layer of PT32 BT film was deposited on the H-MWCNTs/ITO by PSD as the working electrode.A complementary ECD was assembled using the PEDOT film on ITO glass as the counter electrode.It was found that the introduction of H-MWCNTs played a certain role in controlling the surface morphology of PT32 BT films.The PT32 BT film was composed of many three-dimensional nanoparticles with uniform size and close arrangement,and had a large specific surface area.This was conducive to accelerating ion transport,thereby improving the stability of device.Additionally,the introduction of H-MWCNTs greatly improved the electrochemical activity of PT32BT/H-MWCNTs/ITO electrodes,and could shorten the intercalation/deintercalation time of ions at the electrode interface.The ECD-4 assembled with PEDOT/ITO as the counter electrode gradually stabilized after 150 cycles,and the optical contrast of ECD-4 decreased by only 2% from 150 to 270 cycles.(3)Two electrodeposition methods,PSD and PED,were used to prepare P3 DT films on ITO glass.Using bare ITO as the counter electrode,the ECDs were assembled.Then,P3 DT film was used as the electrochromic layer,and the complementary ECD was prepared using PEDOT film prepared by PSD method as an ion storage layer.The results showed that the P3DT-PSD film was continuously stacked with a multi-layer network structure.The film layer spacing was small and tightly bonded to the surface of ITO glass,which was not easy to cause the film to peel off from ITO glass.Moreover,the P3DT-PSD films had a large specific surface area and higher electrochemical activity.Therefore,P3DT-PSD films were beneficial for shortening the ion transport path,accelerating ion transport,and improving the electrochromic performance of devices.The ECD-3 based on P3DT-PSD film had a large optical contrast(25%),a short response time(its coloration time and bleaching time were 1.39 and 0.62 s,respectively),and good cycle stability(after 270 cycles,ΔT decreased from 20% to 15%).