Avoiding Voltage-Induced Degradation in PET-ITO-Based Flexible Electrochromic Devices

Abstract

The cycling stability of flexible electrochromic devices (ECDs) under humid atmospheres is limited by irreversible indium tin oxide (ITO) reduction. A strategy to limit this degradation was developed and tested for model ECDs based on a sidechain-modified poly­(3,4-ethylene dioxythiophene) (PEDOT) derivative and Prussian blue (PB). This work reveals that the cycling stability is reduced by dissolution of the ITO thin films and formation of metallic indium particles on the surface of the ITO layers. The ITO degradation strongly depends on the applied electrode potentials in combination with moisture ingress into the ECDs. To avoid ITO reduction in ECDs, efforts were made to adjust the electrode potentials. ECDs equipped with an auxiliary reference electrode were set up to gather knowledge on the actual electrode potentials. By adjusting the electrode charge density ratio, it was possible to narrow the overall cell voltage window to an extent in which irreversible ITO reduction no longer occurs. Detailed investigation of ECDs with the optimized cell configuration (charge density ratio) showed that the overall device performance with regard to visible light transmittance change and response time is not impaired and that the cycling stability under humid atmosphere (90% rH) is dramatically improved. Thus, the proposed strategy offers an excellent perspective for the commercialization of flexible ECDs upon their enhanced durability.

Probing the Influence of Counter Electrode Structure on Electrochromic‐Device Operating Potentials and Performance Using Electrochemical Impedance Spectroscopy

“…These degradation products can also be observed by visual assessment of the counter electrode after cycling from wide potential ranges, shown in Figure 4 I–J. The formation of surface films creates a dark brown “burned” appearance, similar to what is reported in the literature when ITO undergoes reductive decomposition [48] . In addition, our previous studies have clearly shown that degradation within config.…”

“…The formation of surface films creates a dark brown "burned" appearance, similar to what is reported in the literature when ITO undergoes reductive decomposition. [48] In addition, our previous studies have clearly shown that degradation within config. 1 occurs primarily due to the degradation of the ITO CE and Li-based gel electrolyte, while the electrochromic working electrode remains virtually unchanged.…”

Flexible electrochromic devices prepared on ultra-thin ITO glass

“…As the EC characteristics of Fe-MEPE and PB on FTO glass and PET-ITO were already demonstrated in previous studies, 1,25 only a detailed investigation of Fe-MEPE and PB thin films on ultra-thin ITO glass is described here. The film thickness and surface morphology of the Fe-MEPE and PB electrodes were characterized by scanning electron microscopy (SEM) as shown in Fig.…”

“…23 A typical flexible ECD consists of PET-based, transparent conductive substrates, an EC and ion storage layer, and an ion conductive polymer electrolyte. 24,25 As an alternative to soft polymer-based substrates ultra-thin glass has been gained attention in recent years for various applications such as organic light emitting diodes (OLEDs), 26 electrowetting devices, 27 smart windows, 28,29 and solar cells. 30,31 A few studies of ITO-coated ultra-thin and flexible glass for the aforementioned applications have been conducted.…”

Processable Thiophene‐Based Polymers with Tailored Electronic Properties and their Application in Solid‐State Electrochromic Devices Using Nanoparticle Films

“…[ 30,31 ] The comparison between cast films from chloroform and NPs films from water was performed only for polymers 4 – 6 , since at higher potentials, as required for polymers 1 – 3 , it is visible in the absorption spectra the degradation and color change of PET‐ITO itself. [ 43 ]…”