Rapid Cathodic Coloration in Solution-Processable Electrochromic Polymers of Intrinsic Microporosity

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Conventional electrochromic polymers prioritize planarity for conductivity, hindering ion transport and slowing switching speeds.
• Reduced polymer chain mobility and void space in traditional designs limit electrolyte ion penetration, impacting device performance.

Purpose of the Study:

• To develop solution-processable polymers of intrinsic microporosity (PIMs) for rapid electrochemical switching.
• To investigate the impact of nonplanar polymer design, incorporating spirobisindane units, on electrochromic performance.
• To achieve fast switching times and high optical contrast in solid-state devices.

Main Methods:

• Synthesis of four n-type polymers with distinct chromophores and spirobisindane units.
• Fabrication of solid-state two-terminal electrochemical devices with a gel electrolyte.
• Characterization of polymer properties using CO2 sorption isotherms and electrochemical impedance spectroscopy.
• Evaluation of electrochromic performance, including optical contrast, switching time, and coloration efficiency.

Main Results:

• Achieved rapid electrochemical switching with a 1-second switching time (t95) and >90% optical contrast (ΔT %).
• Demonstrated polymers with large accessible surface areas (>250 m2 g-1), facilitating fast ion transport.
• Obtained high coloration efficiencies (CE) up to 450 cm2 C-1 with excellent stability (>95% retention over 200 cycles).
• Showcased 12 distinct optical profiles from the four polymers, each with two accessible reduced states.

Conclusions:

• Nonplanar polymer design incorporating spirobisindane units enables simultaneous porosity and electrochemical activity.
• Rapid switching speeds in electrochromic devices are achievable through enhanced ion transport facilitated by polymer porosity.
• These findings offer new design principles for organic mixed ionic-electronic conductors for advanced electrochromic applications.