Flexible PEDOT electrodes with large thermoelectric power factors to generate electricity by the touch of fingertips

Abstract

Highly conductive PEDOT films were prepared by solution casting polymerization using finely tuned oxidation solution and used as electrodes for the precise control of the oxidation level of the polymer electrochemically. They exhibited a large power factor of 1,270 mW m À1 K À2 and could be processed as flexible and cuttable thermoelectric films to generate electricity by fingertips.

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

“…[25][26][27][28] However, the steric effect of nonconductive copolymer inhibitors and the challenge of controlling the polymerization should also be considered, particularly careful control of the film thickness. Therefore, PEDOT:DBSA seems to be a better option for applications due to its appropriate basicity, which ensures both good chain conductance and reaction control.…”

“…Such thick films with low sheet resistance (down to 5 Ω) are potentially suitable for various applications such as flexible TE devices or electrode materials, while the PEDOT polymerized using conventional oxidants often suffers a drastic decrease in electrical performance with increasing film thickness due to the uneven evaporation of pyridine and the remaining PEPG. 27,31,33 Effect of the anion on the reaction rate and doping level To explain this self-inhibiting phenomenon, the role of the anion in the polymerization was investigated. According to previous experimental reports, the reaction rate (r total ) is influenced by the concentration of Fe 3+ and H + : 21…”

“…However, OTs and OTf anions have a low affinity for alcohol, which allows only limited (o40 wt%) concentrations in solution and the production of films with low thicknesses of 50-260 nm. [25][26][27][28][29][30][31][32][33] These oxidants are also easily crystallized during the reaction due to their low solubility, and the crystallized oxidants cause the formation of pin-hole defects in the film. 34 The loading of PEPG further reduces the film thickness due to a severe concentrating effect.…”

“…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 for electrical applications because of their compact and ordered polycrystalline structure 23 that leads to higher σ and S. 22,[24][25][26] S-PEDOTs often exhibit large S 2 σ that can be further optimized by tuning the oxidation level. [27][28][29] However, these high quality films are hard to obtain due to their poor reaction controllability and difficult to put into practical use because of their limited film thickness. The ability to control the polymerization process and the structure of the polymer is currently limited due to the lack of research into the role of the anion, which accounts for a large portion of both PEDOT and its precursor.…”

“…30 However, the unequal evaporation of pyridine leads to uneven polymerization and a severe deterioration of σ when fabricating thicker films. 31 In addition to pyridine, copolymer inhibitors, such as poly(ethylene glycol)-blockpoly(propylene glycol)-block-poly(ethylene glycol) (PEPG), are also commonly used to reduce the oxidant reactivity through steric effects and suppress the crystallization of oxidants, 22,[26][27][28][32][33][34][35] but the copolymer phase remaining inside PEDOT causes the deterioration of σ. 33 For both applications as TE devices and electrode materials, PEDOT films with a reasonable thickness are required.…”