Preparation And Properties Of Polythiophene-based Electrochromic Films By Pulsed Electrodeposition

In polymer-based electrochromic devices(ECDs),the electrochromic layer is composed of conducting polymer(CP)film,which can be prepared by dip-coating or spin-coating,chemical oxidative polymerization(COP),oxidative chemical vapour deposition(oCVD),vapour phase polymerization(VPP)and electrodeposition.Among them,the physical coating,COP,oCVD and VPP need either molecular design of CPs,or complex instruments and techniques.In addition,they are difficult in realizing the uniformity of obtained CP films.These drawbacks restrict the application of these methods.In comparison,electrodeposition is a simple,effective,low-cost and easily implemented method,which can control the resulting morphology,composition and thickness of the deposited films.In this paper,we utilized a simple and effective pulsed electrodeposition(PED)method to prepare the polythiophene(PT),poly(2,2?:5?,2??-trithiophene)(PTTh)and poly(3-(2-hydroxyethyl)thiophene)(P3TE)films on indium tin oxide(ITO)glass,and the effects of PED parameters on the morphology,electrochemical and electrochromic properties of polymer films were investigated.The main research contents are as follows:(1)A series of PT films were prepared on ITO glass by pulsed electrodeposition and assembled into the ECDs,and their structure and properties were characterized.The results indicate that PT films obtained by PED exhibit a loose surface morphology,large surface area and high electrochemical activities.The electrochromic properties of the ECDs assembled by these films are significantly improved,which exhibits a large optical contrast,high coloration efficiency,short switching time,and stable cycling.Moreover,it is found that when the time interval of PED is 10 s,the prepared PT film(PT-10)has the best performance.Compared with the ECD based on PT film obtained by potentiostatic deposition(PSD)on ITO glass,the optical contrast of ECD based on PT-10 film(ECD-10)increases by 94%(17?33%),and its coloration efficiency increases by 88%(159?299 cm~2/C).The response time of ECD-10 is shorter with a coloration time of 1.12 s and a bleaching time of 0.80 s.(2)The PTTh films with three-dimensional porous structure were fabricated by PSD and PED,and further assembled into the ECDs.We investigated the structure and properties of PTTh films and corresponding ECDs.The results show that the PTTh film with a PED time of240 s(PTTh-PED-240)possesses loose porous morphology and large surface area.The ECD based on PTTh-PED-240 film exhibits a large optical contrast(45%),high coloration efficiency(534 cm~2/C),short switching time(the coloration time and bleaching time are 2.03 and 0.28 s,respectively),and improved cycling.It is found that the optical contrast of the ECDs based on PTTh-PED films increases almost linearly with the thickness of films,and then decreases slightly when the thickness of films further increases.This indicates that there is a limit in the promotion of PTTh-PED film thickness.(3)The P3TE films were prepared on ITO glass by PSD and PED,assembled into the ECDs,and their structure and properties were characterized.The results indicate that the structure of P3TE-PSD-60 film is uniform and dense,while P3TE-PED-120 film exhibits a loose and rough morphology,where many nanoparticle aggregates are distributed on the surface of film.Thus,P3TE-PED-120 film has large electrochemical active area.The ECD based on P3TE-PED-120 film exhibits a large optical contrast(51%),short response time(the coloration time and bleaching time are 4.34 and 1.86 s,respectively),and improved cycling.Moreover,it is found that the optical contrast of complementary ECD based on P3TE-PED-120 and WO₃-PSD-90 films increases to 53%and its switching speed is fast.This indicates that as a simple,efficient and low-cost method,PED can be widely used in the preparation of high-performance polymer films in complementary ECDs.