Dispositivos eletrocrômicos com base em PEDOT:PSS: deposição por rolos e a Influência da distribuição do eletrólito na eficiência do dispositivo

Abstract

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) denoted as PEDOT:PSS, a common material used as electrode in organic electronics as charge balancing layer in electrochromic devices, was processed in thin film by roll-to-roll technique onto flexible substrate. Improved wettability was achieved when the ITO/PET substrate received a pre-treatment with isopropyl alcohol (iPrOH) and small amount of this alcohol was mixed with the PEDOT:PSS, as demonstrated by the reduction of the contact angle. Besides allowing the preparation of uniform films in larger areas, this procedure also resulted in PEDOT:PSS films with increased conductivity, this arises from the effect of the alcohol that: spreads out the isolating PSS moietes from the surface of conducting PEDOT moieties and/or modify the PEDOT chain conformation, resulting in increased conductivity. These roll-to-roll processed PEDOT:PSS films were tested in electrochromic devices having a polymer:solid electrolyte composite based on poly(ethylene oxide) and lithium perchlorate. This device was sealed by lamination procedure in air. The contrast between oxidized (light blue) and reduced (dark blue) state of PEDOT:PSS was monitored by UV–Vis transmittance. The use of iPrOH as a additive resulted in improvement of the electrochromic response with coloration efficiency of 377 C-1 cm2 after 0.3 s of switch time. Additionaly, for comparison purposes, two flexible electrochromic devices based on PEDOT:PSS were prepared by roll-to-roll technique, these devices were built with the conventional layered geometry or using PEO:LiClO4 and charge balancing material mixed at the same layer. Analysis of the properties leads to the conclusion that the presence of the percolation channels of PEDOT:PSS inside the PEO:LiClO4 results in the performance improvement as monitored by impedance spectroscopy and the respective Randles equivalent circuits. From mixed electrochromic layer, coloration efficiency increases up to 1750 C-1cm2 after 1.5 s of switch time, while the corresponding layered device showed coloration efficiency of 900 C-1cm2 at the same time interval.