Fabrication of long-term stable electrochromic device based on high-quality PEDOT film

As one of representative conducting polymers (CPs), poly(3,4-ethylenedioxythiophene) (PEDOT) possesses fascinating electrochromic properties and commercial applications, but it suffers from the poor cycling stability in the charge-discharge process. In this work, we adopted a dual-approach mode to prepare high-quality PEDOT film in boron trifluoride etherate (BFEE) system via reducing the initial oxidation potential (Eonset) of 3,4-ethylenedioxythiophene (EDOT) monomers to increasing the conjugation degree of PEDOT films and no requiring the addition of other supporting electrolytes to protect the initial structure of PEDOT films. The Eonset of EDOT monomers in BFEE system was only 0.5 V, which was much smaller than other systems reported (1.00-1.26 V). The obtained PEDOT film with porous structure showed remarkable stability with an electrochemical activity retention rate of 91.5% after 190,000 cycles, and that of its electrochromic device (ECD) was 94.23% after 41,000 s. During the redox process, ECD had three color transformations (brown red, cyan, and blue) and the oxidation time and the reduction time were 0.4 s and 1.2 s, respectively. The calculated CE value reached 120 cm2 C-1. All these results suggest that the dual-approach mode can significantly enhance the quality of PEDOT film and thus enhance its cycling stability. In addition to that, the dual-approach mode can provide an effective strategy for the design of highly stable CPs for fabricating long-term stable ECD.