ITO-Free Solution-Processed Flexible Electrochromic Devices Based on PEDOT:PSS as Transparent Conducting Electrode

Abstract

Electrochromic devices (ECDs) are emerging as novel technology for various applications ranging from commercialized smart window glasses, goggles, and autodimming rear view mirrors to uncommon yet more sophisticated applications such as infrared camouflage in military and thermal control in space satellites. The development of low-power, lightweight, inexpensive, and flexible devices is the need of the hour. In this respect, utilizing PEDOT:PSS as transparent conducting electrode (TCE) to replace indium tin oxide (ITO) and metal based TCEs for ECDs is a promising solution for the aforementioned requirements. In this work we have demonstrated the performance of PEDOT:PSS films coated on flexible substrates, treated with PTSA-DMSO, as TCEs for ECD applications and their comparison with that of ITO based ECDs. The PEDOT:PSS based flexible TCEs used in this study have conductivity of 1400-1500 S·cm and figure of merit (FoM) of 70-77. The process of increasing the conductivity of PEDOT:PSS films also led to the broadening of the conducting potential window (CPW), which is important for electrochemical applications of PEDOT:PSS when used as a stand-alone electrode. More than achieving a comparable electrochromic contrast, switching time, and coloration efficiency with respect to the ITO based ECDs, PEDOT:PSS devices also had the added advantage of good mechanical flexibility. These devices demonstrated superior stability during electrochemical cycling and multiple mechanical bending tests, making them an inexpensive alternative to the costly ITO based ECD technology.

Transparent Wood Smart Windows: Polymer Electrochromic Devices Based on Poly(3,4‐Ethylenedioxythiophene):Poly(Styrene Sulfonate) Electrodes

“…At −1.0 V, acid‐treated PEDOT:PSS is rendered insulating, whereas this transition occurs at −0.8 V for the untreated films. The difference in this onset of dedoping is consistent with previous reports and is likely a result of the enhanced ordering of the PEDOT chains 46, 47. This ordering extends the effective conjugation length of the polymer and reduces the oxidation potential for a portion of the p TSA/EG‐treated material.…”

“…Recently, Kumar and co‐workers demonstrated fast‐switching ECDs composed of complimentary poly[3,4‐di‐(2‐ethylhexlyoxy(thiophene)‐ co ‐(3,4‐ethylenedioxythiophene)] and Prussian blue‐based electrochromes deposited on PEDOT:PSS electrodes treated with dilute 1  m para ‐toluene sulfonic acid/dimethyl sulfoxide ( p TSA/DMSO). These ECDs achieved a 40 % device contrast at switching times of less than 2 s 46. Not only were these conductivities suitable to support fast‐switching devices, but the post‐treatments also lowered the PEDOT:PSS dedoping onset potential from −0.57 V for untreated films to −0.72 V versus Ag/Ag + 47, 48.…”

Conductive, Solution‐Processed Dioxythiophene Copolymers for Thermoelectric and Transparent Electrode Applications

“…Energy Mater. [19,23,43,46,47] This difference between the color neutrality of oxidized PE 2 and PEDOT has been previously investigated [19] and can be quantitatively observed by comparing the colorimetry of doped PE 2 films, either with ( Figure 3b) or without ( Figure S4b, Supporting Information) an oxidized film of PProDOT, with the reported values for PEDOT:PSS. This switching is reversible, albeit somewhat slower compared to using an ITO electrode due to the lower conductivity of doped PE 2 ( Figure S7, Supporting Information).…”

“…After an initial electrochemical conditioning between 0.8 and back to -0.2V, the charge neutral peak of PProDOT appears with the typical vibronic features and vibrant magenta/purple color [31] seen in Adv. [43][44][45] While electrochromic polymers on these films switch more rapidly than on doped PE 2 , the films are significantly more colored than the PE 2 -based films due to tailing of the PEDOT bipolaron band. 2019, 9,1900395 Figures 3 a,b, respectively, when the potential is set at -0.2 V. When the potential is changed to 0.8 V the visible absorption of the PProDOT is bleached (ΔT = 48%) and the film becomes color-neutral, as shown in Figure 3b (also see Figure S6 in the Supporting Information).…”

“…[43][44][45] While electrochromic polymers on these films switch more rapidly than on doped PE 2 , the films are significantly more colored than the PE 2 -based films due to tailing of the PEDOT bipolaron band. [19,23,43,46,47] This difference between the color neutrality of oxidized PE 2 and PEDOT has been previously investigated [19] and can be quantitatively observed by comparing the colorimetry of doped PE 2 films, either with ( Figure 3b) or without ( Figure S4b, Supporting Information) an oxidized film of PProDOT, with the reported values for PEDOT:PSS. [44] As a control experiment, a film of PProDOT was cast on a glass slide without the doped PE 2 film under it, and electrochemical potentials were applied in an electrolyte solution in the same manner as with the PE 2 film.…”