Conjugated polyelectrolytes (CPEs) are conjugated polymers with pendant ionic functionalities. Because of the strong hydrophilic interaction between CPE conjugated backbone and carbon nanotubes, a variety of CPEs have been developed for dispersing carbon nanotubes in polar media for solution-processing. However, there are few studies on the charge-transfer between CPE dispersants and carbon nanotubes. No n-type CPE/carbon nanotube composites have been reported previously.
Thermoelectric generator can convert heat gradient directly to electricity, and it is regarded as a clean and quit renewable energy conversion technique. The current available thermoelectric materials are inorganics, which are toxic and brittle. Conductive polymers and their composites are attractive for several reasons, such as flexibility, light-weight, synthetic versatility, low toxicity, and so on. Thermoelectric devices require both p- and n-type conductive materials. However, highly conductive n-type organic materials are very rare.
This talk focuses on the thermoelectric properties of self-doped conductive CPEs and their composites with single-walled carbon natotubes (SWNTs), and the application in the emerging field of flexible thermoelectrics. First, we synthesized a series of narrow band gap anionic CPEs with the same conjugated backbones, but with different counterions and alkyl chain lengths. These CPEs are found to be doped during dialysis as part of the purification process to furnish conducting materials. CPEs with smaller counterions and shorter alkyl chain length exhibit relatively higher electrical conductivity, but comparable Seebeck coefficients. Second, these CPEs can disperse SWNTs in polar media (water and methanol) for preparing conductive films via solution processing. Third, we show how to tune the thermoelectric properties (electrical conductivity and Seebeck coefficients) of CPE/SWNT composites by varying the CPE structures, including the conjugated backbones and ionic functionalities. Seebeck coefficient measurements confirmed that we have obtained both p- and n-type conductive CPE/SWNT composites. Lastly, we have successfully used these materials (both p- and n-type) to fabricate a flexible thermoelectric device. This device is stable at ambient conditions, and can efficiently convert heat gradient to electricity. The fabrication and performance of this thermoelectric generator will be discussed.