All Polymer Solution Processed Electrochromic Devices: A Future without Indium Tin Oxide?

Abstract

The growing range of applications for optoelectronic and electrochromic devices (ECDs) encourages the search for materials combining high electrical conductivity with optical transparency. Next generation transparent conducting electrodes (TCEs) are required to be inexpensive, lightweight, scalable, and compatible with flexible substrates to trigger innovations towards supporting sustainable living and reducing energy consumption. Here we show that PEDOT:PSS can be solution processed using blade coating and subsequently post-treated with nitric and acetic acid to raise its conductivity above 2000 S cm with a film transparency of ∼95%. A combined grazing-incidence wide angle X-ray scattering, atomic force microscopy, and thickness analysis of the film indicates that the removal of excess insulating PSS inducing reordering is the critical parameter for the claimed conductivity increase. We then investigate the impact of replacing indium tin oxide electrodes with PEDOT:PSS in ECDs. While electrochromic contrast and optical memory are comparable for devices constructed with both electrode materials, differences in switching kinetics are explored by comparing internal resistances, ion diffusion, and charging effects in the polymer films extracted by electrochemical impedance spectroscopy. While all these ideas are described based on a battery-type ECD configuration, these concepts are easily transferable to other types of redox-active devices.

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

“…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).…”

“…PEDOT:PSS films have also found use as transparent electrodes for electrochromic polymers and other applications. [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.…”

Paper‐Based Electrochromic Devices Enabled by Nanocellulose‐Coated Substrates

“…However, since silver is electrochemically active in the same potential range as the majority of cathodically coloring electrochromic polymers (ECPs), it makes sense to eliminate it as an electrode material and utilize solely PEDOT:PSS. In addition to being redox‐stable, PEDOT:PSS can be rendered highly conductive using a variety of acidic post treatments . As it can be easily formulated into printable, aqueous inks, PEDOT:PSS is a promising candidate for transparent electrodes applied to paper ECDs.…”

A new green‐to‐transmissive polymer with electroactive poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) as an interface layer for achieving high‐performance electrochromic device

“…Poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a water‐soluble conductive polymer has received extensive attention in the field of organic electroluminescence, solar cell, and sensor . Kim et al demonstrated that PEDOT:PSS films with highly enhanced conductivity and stability by heating treatment could serve as a promising transparent electrode for low‐cost and flexible ITO‐free organic solar cells.…”

“…Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a water-soluble conductive polymer has received extensive attention in the field of organic electroluminescence, solar cell, and sensor. [31,32] Kim et al [33] demonstrated that PEDOT:PSS films with highly enhanced conductivity and stability by heating treatment could serve as a promising transparent electrode for low-cost and flexible ITO-free organic solar cells. Hsiao and coworkers [34] prepared Ni(OH) 2 /PEDOT: PSS composites ["P-Ni(OH) 2 "] that enhanced the electric/ionic transport properties of pristine Ni(OH) 2 , and significantly reduce the charge transport barrier.…”