Micron-thick highly conductive PEDOT films synthesized via self-inhibited polymerization: roles of anions

The inhibitor-dependent poly(3,4-ethylenedioxythiophene) (PEDOT) fabrication suffers major problems in the areas of controllability and film thickness. In this work, we found that anions play a key role in both the polymerization and the structure of PEDOT. As a precursor, anions greatly influence the reaction rate and oxidant solubility. In its role as a counter-ion, the anions also affect chain conductance and crystal growth. With these behaviors in mind, a self-inhibited polymerization approach using novel oxidants with appropriate anions was successfully developed to facilitate the fabrication of high quality in situ polymerized PEDOT films and solve the thickness limitation problem. Inhibitor-free heavy oxidative solutions with weakly basic anions enable the spin-coating of thick and homogeneous oxidant layers and also effectively inhibit both the crystallization of the oxidant and H+ formation throughout the polymerization process. PEDOT: dodecylbenzenesulfonate (PEDOT:DBSA) exhibits the highest performance among all candidates due to its appropriate anion basicity and low steric effect. An extremely high doping level of 42.9% is achieved, and an electrical conductivity of ~1100 S cm−1 is successfully maintained for film thicknesses between 310 nm and 1.79 μm. In addition, the thermoelectric power factor (RT) for pristine films was improved to 77.2 μW mK−2 from 69.6 μW mK−2 by the dedoping treatment. This study provides a new approach for fabricating high performance PEDOT thick films using anion-based design. The use of ferric salts can improve the thermoelectric properties of organic films, which could be used to recover energy from waste heat. Thermoelectric materials convert heat into electricity, offering an exciting route to enhance the energy efficiency of industrial processes. But better materials are required before this technology becomes widely adopted. Now, Lidong Chen from the Shanghai Institute of Ceramics, China, and colleagues have evaluated the thermoelectric performances of a common organic material called PEDOT synthesized with three iron-based oxidants. They found that these ferric salts stabilized the polymerization of PEDOT, enabling homogeneous, micrometer-scale films to be synthesized by a simple one-step process. The films also exhibited excellent electrical conductivity. This method provides a new approach for fabricating thick, high-performance PEDOT films that involves designing the anions used. Micron-thick highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) films are fabricated using a novel self-inhibited polymerization (SIP) approach. The newly adopted inhibitor-free heavy oxidative solutions containing weakly basic anions (WBAs) such as dodecylbenzenesulfonate (DBSA) enables the spin-coating of thick and homogeneous oxidant layer, and meanwhile effectively inhibits both the crystallization of the oxidant and the H+ formation throughout the polymerization process.