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. NPG Asia Materials (2017) 9, e405; doi:10.1038/am.2017.107; published online 14 July 2017 INTRODUCTION Thermoelectric (TE) materials realize direct conversion between heat and electricity, which can be used in refrigeration and power generation. The performance of TE materials is characterized by the ZT value (S 2 σT/κ) or power factor (S 2 σ), where S, σ, T and κ are the Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity, respectively. Conducting polymer TE materials possess the advantages of low κ, good flexibility and low cost in comparison with inorganic materials. 1-4 Among them, commercially available PEDOT:polystyrenesulfonate (PEDOT:PSS) has received the most attention due to its excellent water processability and high σ ( refs 5-11 ) and is also widely used as an electrode or conductive adhesive material in applications including solar cells, 12,13 organic light-emitting diodes (OLEDs), 14,15 supercapacitors, 16,17 sensors 18,19 and so on. The PSS polyanion enables the formation of aqueous PEDOT:PSS solutions, which benefits both film printing and the synthesis of hybrid materials. However, such PSS-based processes also experience difficulties with performance optimization. For example, the insulating PSS lamellas remain in the polymer matrix, 20,21 resulting in an amorphous polymer 22 with limited σ and S. 5,9 Compared to PEDOT:PSS, PEDOT doped with smallsized anions (S-PEDOTs), such as tosylate (OTs) or triflate (OTf), have greater potential...
