Polymer-based Electrochromic Devices Research Articles

Structural optimization of ion storage layer for highly stable electrochromic devices based on polythiophene derivative films

Due to their rich color, fast switching speed and high coloration efficiency, polymer-based electrochromic devices (ECDs) have broad application prospects in various fields such as smart windows, anti-glare rearview mirrors, displays and adaptive camouflage. However, the preparation of highly stable polymer-based ECDs is still a great challenge. Herein, we present a simple and efficient strategy to construct the poly (3,4-ethylenedioxythiophene) (PEDOT)-multi-walled carbon nanotubes (MWCNTs) composite film or PEDOT/MWCNTs bilayer film, which serves as ion storage layer. The ECDs are assembled with poly (3-hexylthiophene) (P3HT) as EC layer due to its good EC behavior. The P3HT film was prepared by potentiostatic deposition, and the PEDOT, PEDOT-MWCNTs and PEDOT/MWCNTs films were obtained by spray-coating technology. We investigated the structure, morphology and electrochemical performance of P3HT, PEDOT, PEDOT-MWCNTs and PEDOT/MWCNTs films, and EC properties of devices. The results indicate that the rough and porous P3HT film consists of many nanoparticles. Compared with PEDOT-MWCNTs composite film, the PEDOT/MWCNTs film is more loose and porous, where PEDOT nanoparticles and some PEDOT nanosheets are coated on a three-dimensional skeleton film of MWCNTs. These films possess good electrochemical performance. The ECD based on P3HT and PEDOT/MWCNTs films achieves an optical contrast of 38 % and coloration efficiency of 375 cm2/C, exhibiting good cyclic stability (retaining 92 % of initial optical contrast after 2000 cycles). Its coloration time and bleaching time are 0.60 and 1.83 s, respectively. This study suggests that structural optimization of ion storage layer might be a facile strategy for fabricating highly stable polymer-based ECDs.

Random copolymer design strategy towards excellent electrochromic display devices with fast responses

The development of polymer-based electrochromic devices (ECDs) with high stability and fast response time is of utmost importance for their effective utilization in ECD displays. In this study, we took inspiration from the random copolymer design strategy and successfully synthesized three solution-processable polymers, namely PTQ1, PTQ2, and PTQ3. These polymers were created using propylenedioxythiophene (ProDOT) as the donor unit and 5,8-dibromo-2-((2-ethylhexyl) oxy) quinoxaline (QX) as the acceptor unit, with varying feed ratios of ProDOT to QX (1:1, 2:1, and 3:1, respectively). Remarkably, all three polymers exhibited remarkably low oxidative initiation potentials and effective overpotentials, resulting in their respective ECDs displaying impressively fast response times of 1.8 s for PTQ1, and 0.9 s for both PTQ2 and PTQ3. Furthermore, these electrochromic polymers demonstrated exceptional stability, as indicated by their ability to maintain nearly 90% optical contrast even after 100,000 reversible switching cycles. This finding underscores the high stability of PTQ2 and PTQ3 when integrated into devices, highlighting their suitability for incorporation into future applications. Notably, owing to their fast response time and excellent reversibility, we were able to successfully fabricate two types of ECDs based on PTQ3: an inkjet-printed patterned ECD, as well as a larger 10 × 10 cm2 ECD. These achievements demonstrate the immense potential of the random copolymer strategy not only in the field of display technology but also in the development of smart windows. In conclusion, our research has successfully synthesized and characterized three solution-processable polymers for use in polymer-based ECDs. By employing the random copolymer design strategy, we have achieved impressive stability, fast response times, and high reversibility. These findings pave the way for the implementation of these electrochromic polymers in a wide range of applications, including displays and smart windows.

Design of Dithienopyran-Based Conjugated Polymers for High-Performance Electrochromic Devices

Numerous conjugated polymer-based electrochromic devices (ECDs) have been developed, but the correlation between electronic properties of electrochromic polymers (ECPs) and their EC performance, especially response speeds, has been rarely explored. In this work, we propose two new dithienopyran-based ECPs containing different heteroatoms with distinct electronic characteristics to elucidate the effect of the electronic structure of ECPs on EC performance. When electron-donating alkoxy groups are fused into ECPs (P(DT-P)), their highest occupied molecular orbital energy level becomes higher than the alkylthio (electron withdrawing group)-containing ECPs (P(DT-TP)) and the oxidation of P(DT-P) is easier. In addition, the P(DT-P) in the oxidized state is relatively stable due to the stabilization through the resonance of the lone-pair electron of the oxygen atom. These features contribute to the rapid bleaching of the P(DT-P) (∼0.5 s). In contrast, the alkylthio group of P(DT-TP) pulls electrons and destabilizes the radical cation in the oxidized state. Thus, when the P(DT-TP) is oxidized (bleached), the recovery to the neutral state (colored state) is preferred, leading to fast coloration (∼0.4 s) and unprecedentedly high coloration efficiency (∼1323 cm2/C). Both systems can retain more than 90% of their initial optical contrast after 5000 cyclic switchings, indicating their high feasibility for commercialization.

Cost-Effective, Flexible, and Colorful Dynamic Displays: Removing Underlying Conducting Layers from Polymer-Based Electrochromic Devices.

Electrochromic (EC) materials and devices provide a user-controlled, dynamic way of displaying information using low power, making them interesting for a range of applications in numerous markets, including logistics, retail, consumer goods, and health care. To optimize the cost while simplifying the production, expanding the color space, and enhancing the contrast and vibrancy of EC displays aimed for cost-sensitive products, we sought to reduce the number of layers as well as remove the underlying conducting layer that accounts for a substantial fraction of the cost of a printed label. Here, we show how conjugated electrochromic polymers, which are inherently semiconducting, can be used to accomplish this goal and afford printable EC displays with a flexible form factor. Using a combination of electrochemical probes, in situ spectroscopy, solid-state conductivity, and in situ conductance measurements, we have studied and compared five different EC polymers with conductivities spanning multiple orders of magnitude and colors that span most of the visible range, identifying polymers and properties that allow for switching from the colored to the clear state without an underlying conducting layer. Finally, we incorporate these EC polymers into optimized flexible devices without an underlying conductor and demonstrate that they are able to provide on-demand, reversible colored-to-clear switching on the order of seconds to minutes, with operating voltages below ±1 V, optical memories exceeding 60 min, and a shelf-life exceeding 12 months.

Photostability of Ambient-Processed, Conjugated Polymer Electrochromic Devices Encapsulated by Bioderived Barrier Films

Polymer-based electrochromic devices (ECDs) are a promising technology for enabling low-voltage, disposable displays, yet are currently limited by photo-oxidative bleaching of the active materials....

From the bottom up--flexible solid state electrochromic devices.

Solid-state flexible polymer-based electrochromic devices are fabricated continuously by stacking layers in one direction. This novel bottom-up approach with no need for a lamination step is realized through in situ photo-crosslinking of the electrolyte using a "curing-chamber" fitted to a roll-coater, which lowers the oxygen concentration at the electrolyte surface. This enables fully printed and 2D patterned organic electrochromics.

Polymer-based electrochromic devices—I. Poly(3-methylthiophenes)

The basic aspects of electrochromism induced by a p-doping/undoping process of conjugated polymers are briefly described. The most important requisites for an electrochromic device are discussed, and polymer electrochromic performance data as well as the test results of a polymer-based variable light transmission electrochromic device are reported. The colour contrast control of conjugated polymers by “tailoring” their conjugation length is discussed and spectroelectrochemical data of poly(3-methylthiophenes) electrosynthesized from 3-methylthiophene isomeric dimers and isomeric tetramers are reported.

Polymer-based electrochromic devices

Electrochromic phenomena related to p-doping-undoping process of thiophene-based polymers are briefly described. Electrochromic performance data of poly(2,2'-bithiophene) and poly(3-methylthiophene) polymers, electrosynthesized from 2,2'-bithiophene and 3-methylthiophene commercial products in optimized conditions, to evaluate the possibility of their use in electrochromic devices are surveyed, and the test results of a poly(3-methylthiophene)-based electrochromic device operating in transmissive mode with counter electrode optically passive are reported. Finally, electrochromic performance data of 3-methylthiophene polymers with “tailor-made” conjugation length through electrochemical polymerization of 3-methylthiophene dimers are reported and discussed.