Electrochemical Preparation And Electrochromic Performance Of Poly(3-methylthiophene)films

With Chinese continuous urbanization construction growing,building energy consumption has increased rapidly in recent years.The refrigeration,heating,and lighting energy consumption of public buildings still account for major proportions of the building operation energy consumption.Among all kinds of new building energy saving technologies,electrochromic(EC)smart windows technology,which could dynamically adjust sunlight and thermal energy,has drawn substantial attentions.At present,inorganic electrochromic smart window materials have been produced and commercialized.However,the organic electrochromic materials were barely achieved industrialization due to their high price of monomer,complex prepared process,and poor stability.In this paper,poly(3-methylthiophene)(PMeT)electrochromic film was studied to overcome these problems by several strategies,like pre-nucleation treatment,thermal aftertreatment,copolymerization and construction of nanostructures.Finally,we got a PMeT film which possesses multi-colors switches,easier processing method and excellent EC cyclic stability.Furthermore,the relationship between structure change and cyclic stability was discussed.Firstly,we used galvanostatic method to grew poly(3-methylthiophene)film,and found the film exhibited non-uniformity regardless of any growing conditions.It is mainly caused by the disordered distribution of nucleation,which essentially attributes to the instantaneous nucleation growth mechanism.For resolving this question,we presented a new pre-nucleation method during film growing.It was 75m A/cm~2 of 0.2 s applied for nucleation,then 4 m A/cm~2of different time applied for film growth.The uniformity of the film was effectively improved after using this method,the root square roughness reduced from 0.086 to 0.024.The thickness of film could be controlled(from 100 nm to 1.5±0.2?m)by adjusting second step`s time.The electrochromic properties of films varied with thickness changing,the best transmittance switched from 18%to 94%at the wavelength of 1050 nm,and the contrast retained 46.2%after 400 cycles.In addition,different temperatures were used to thermal-treat the pre-nuclear PMeT films.The film`s conductivity and EC cycling stability were improved after thermal treatment.The contrast could remain84%after 400 cycles.The bleaching and coloring time was 0.5 s and 1.4 s,respectively.Secondly,the P(EDOT-Me T)films were copolymerized by constant voltage in electrolyte mixed by EDOT and Me T monomer.The monomer ratio,polymerization voltage and polymerization time could affect the films`structure,composition and electrochromic properties.After comparison,the best process condition was obtained,which applied 2.0 V of 30 s to polymerized in the electrolyte of monomer ratio(EDOT:Me T)of 3:100.This film displayed high uniformity and density,controllable thickness and multi-color change.Furthermore,EC cyclic lifetime of this film was extended to 1000 cycles.The contrast remained 98.7%after 1000 cycles.Finally,P(EDOT-Me T)was electrochemical polymerized into the gap of PS templates.After etching of PS templates,the porous P(EDOT-Me T)films were obtained.The pores were well-structured and interconnect.The diameter of pores varied with the PS diameter,including about 700 nm?500 nm and 400 nm.Among them,700 nm P(EDOT-Me T)film had largest contrast of 69.9%at the wavelength of1050 nm.And the 400 nm P(EDOT-Me T)presented fastest response,the bleaching and coloring time was 0.44 s and 0.73 s,respectively.All the films displayed remarkable EC response after 3000 switches,and their contrast exhibited three steps degradation in different speeds during these cycles.By analogy with the similar structured PEDOT,it was concluded a mechanism of three-steps`structure changes of"ions trapping-deposition appearance-deposition fully covered",which resulted different decay rates of contrast.It could be verified by morphology measures and composition characterizations.