Chloride Transport in Conductive Polymer Films for an n-Type Thermoelectric Platform
The Cl− transport in conductive polymer (CP) film was demonstrated for n-type thermoelectric (TE) harvesting. CPs have been considered as an important group of p-type TE materials due to their high TE functionalities plus simple processing steps for a device. In particular, recently emerging p-type ionic CPs could be unique candidates due to their high Seebeck coefficients (S). However, n-type materials based on CPs suffer from very poor TE functionalities and n-type ionic TE CP materials have not been realized so far. Here, we report the first example of n-type mixed ionic−electronic CP composite (NPC) films. The p-type nature of the PEDOT:PSS films was drastically converted into n-type nature in the presence of CuCl2 through metal binding with polymers and thus formation of Cl− channels. A fluorescence imaging using as a Cl− indicator and time-of-flight secondary ion mass spectrometry mapping confirmed that Cl− transports in the film from hot to cold electrode. In addition, electron spin resonance spectrum indicated major spin density transition from a polaron of the PEDOT:PSS to the polymer bound unpair electron spin of Cu ion by increasing CuCl2 content, to prove the binding of metal ions with PSS unit of the polymer chain. These mixed ionic−electronic NPC films recorded a surprisingly high negative S of over −18.2 mV K−1 and a power factor of 1.7 mW m−1 K−2 at 80% RH with 40 wt% of CuCl2. Taking advantage of this high performance, the CP films were integrated with a p-type CP film as a flexible module-type TE harvester with 10 pairs of p-n legs on CNT electrodes. This TE harvester showed 1.55 V of thermovoltage for a low temperature gradient of 4.5 K. This high anion transport in a TE CP hydrogel film might be a useful solution for environmentally benign and body-worn electronics.