Controlling morphology, adhesion, and electrochromic behavior of PEDOT films through molecular design and processing

Abstract

AbstractPoly(3,4‐ethylenedioxythiophene) (PEDOT) is a well‐known semiconducting polymer with favorable properties which find it often applied as the active material in biological sensors and electrochromic devices. However, PEDOT has several drawbacks which can prohibit its effective or long‐term use, including weak adhesion to substrates such as ITO‐coated glass, poorly controlled surface morphology, and reduced electrochemical stability over time. While a diverse range of approaches have been explored to overcome these issues, most involve additives or substrate modification, while solutions based on direct covalent adaptation are relatively lacking. We present a novel polymer based on covalently modified EDOT (PEDOT‐Crown), featuring polar motifs and a 15‐crown‐5 moiety. Compared to PEDOT, PEDOT‐Crown demonstrates a wealth of advantageous properties including: superior adhesion to ITO under physical and electrochemical duress; a more uniform surface morphology; and electrochemical properties including a higher contrast ratio, red‐shifted polaron and bipolaron absorption features, bleaching of the neutral absorption band across a narrower voltage range, and more Faradaic rather than capacitive behavior. Additionally, we note that in the presence of Na+, PEDOT‐Crown appears to show modified behavior in long‐term electrochemical experiments. These features make PEDOT‐Crown a material with improved suitability for application in biological sensing and electrochromic devices, compared to PEDOT.