Abstract
AbstractConjugated electrochromic (EC) polymers for flexible EC devices (ECDs) generally lack a fully colorless bleached state. A strategy to overcome this drawback is the implementation of a new sidechain‐modified poly(3,4‐ethylene dioxythiophene) derivative that can be deposited in thin‐film form in a customized high‐throughput and large‐area roll‐to‐roll polymerization process. The sidechain modification provides enhanced EC properties in terms of visible light transmittance change, Δτv = 59% (ΔL* = 54.1), contrast ratio (CR = 15.8), coloration efficiency (η = 530 cm² C−1), and color neutrality (L* = 83.8, a* = −4.3, b* = −4.1) in the bleached state. The intense blue‐colored polymer thin films exhibit high cycle stability (10 000 cycles) and fast response times. The design, synthesis, and polymerization of the modified 3,4‐ethylene dioxythiophene derivative are discussed along with a detailed optical, electrochemical, and spectroelectrochemical characterization of the resulting EC thin films. Finally, a flexible see‐through ECD with a visible light transmittance change of Δτv = 47% (ΔL* = 51.9) and a neutral‐colored bleached state is developed.
Highlights
Devices (ECDs), as non-light emitting, low weight and low power interactive graphics, generally lack a fully colorless bleached state
The results indicate a reversible redox switching behavior with only a small drop of charge density in the first 1000 cycles (0.1 mC cm−2), which can be attributed to the formation processes and further electrochemical polymerization of the polymer chain
After 10 000 switching cycles, the PEDOT-EthC6 thin film on PET-ITO shows a total charge retention of more than 91%, the charge density decreases from 3.5 to 3.2 mC cm−2
Summary
The ISP film exhibits reversible redox peaks at a potential of 2.8 V (cathodic scan) and 2.5 V (anodic scan) versus Li/Li+ (ΔEp = 300 mV) corresponding to the oxidation (bleaching) and reduction (coloring) process, respectively, of the conjugated backbone. The measurement was performed by charging and discharging the PEDOT-EthC6 thin film on PET-ITO in a 1 m LiClO4/PC electrolyte with a current density of 50 μA cm−2. The visible light transmittance change Δτv can be calculated as 47% (ΔL* = 51.9) and the contrast ratio CR is estimated to be 16.7, a result which clearly outperforms the properties of commonly used PEDOT-based ECD.[9] the response time, which is considered to be the time corresponding to a current drop to 10% of the starting (maximum) value, was analyzed in a potentiostatic experiment (Figure 7B). The cycling stability of the ECD (100 cycles) is shown in Figure S9 in the Supporting Information, where the enhanced durability is demonstrated with a total charge retention of more than 97%
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