Organic Polymeric Electrochromic Devices:  Polychromism with Very High Coloration Efficiency

• Published in: Chemistry of materials Vol. 16; no. 4; pp. 574 - 580
• Main Authors: Sonmez, Gursel, Meng, Hong, Wudl, Fred
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 24-02-2004
• Subjects: Applied sciences; Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; General and physical chemistry; Physicochemistry of polymers; Physics; Polymers; Inorganic compounds; Organic compounds
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm0301773

The electrochromic properties of electrodeposited poly(1,4-bis(2-[3‘,4‘-ethylenedioxy]thienyl)-2-methoxy-5-2‘ ‘-ethylhexyloxybenzene) (P(BEDOT-MEHB)), a material for polymer electrochromic displays, are reported in detail. While the polymer is transparent in the fully oxidized state, two absorption bands obtained in the visible region for the neutral and partially oxidized polymer are due to two different colors from the same material. Compared to other inorganic or organic electrochromic materials, the P(BEDOT-MEHB) films exhibited very high coloration efficiency values:  as high as 680 cm2/C at 535 nm and −360 cm2/C at 760 nm. The films have the advantage of exhibiting cathodic and anodic coloration. The space created by the methoxy ethylhexyloxy benzene between EDOT units on the polymer backbone makes the injection/rejection of the negatively charged counterions inside/outside of the polymer easier, resulting in higher doping levels than PEDOT at the same optical density. Very well-defined electrochemistry, high level of stability to overoxidation and long-term switching, and the chromicity properties mentioned above make P(BEDOT-MEHB) an excellent candidate for electrochromic displays.