Symmetrical electrochromic device from poly(3,4-(2,2-dimethylpropylenedioxy)thiophene)-based semi-interpenetrating polymer network

A simple chemical method for assembling all-plastic symmetrical conducting polyethylene oxide (PEO)/poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProDOT-Me2) semi-interpenetrating polymer networks (semi-IPNs) has been used leading to interesting electrochromic device. The ProDOT-Me2 monomer was synthesized by trans-etherification in good yield from 3,4-dimethoxythiophene and 2,2-dimethylpropane-1,3-diol. The chemical polymerization of the ProDOT-Me2 inside a thin film of PEO network was performed using FeCl3 as oxidant. The conditions of polymerization lead to an anisotropic repartition of the electronically conducting polymer, mainly present on each face of the semi-IPN. The visible optical absorptions and IR reflectivity were determined after chemical oxidation (p-doping) and reduction (dedoping) of the PProDOT-Me2 within the semi-IPN. The highest optical contrast measured in transmission at 574 nm was 62% for a semi-IPN containing 1.8% PProDOT-Me2. For a similar system containing more PProDOT-Me2 (3 wt%), the semi-IPN becomes opaque and exhibits near infrared and middle infrared reflexion contrast. Then a symmetrical electrochromic device (SECD) was constructed after swelling the semi-IPN (1.8 wt% PProDOT-Me2) in a 0.1 M LiClO4/propylene carbonate electrolyte solution and sandwiching the semi-IPN between two transparent ITO electrodes. The SECD exhibits a maximum contrast of 32% at 574 nm upon electrochemical commutation between 0 and 1.2 V.

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► A symmetrical electrochromic device is built from semi-IPN architecture.
► Diffusion of monomer inside the network is controlled by solvent polarity.
► Poly(ProDOT-Me2) is used as electrochromic layer.
► Semi-IPN exhibits tuneable optical properties in visible and middle IR according to poly(ProDOT-Me2) content.
► Optical transmittance measurements of the optimized device show 32% of contrast in the visible region.