Alcohol-Processable All-Polymer n-Type Thermoelectrics

The general strategy for n-type organic thermoelectric is to blend n-type conjugated polymer hosts with small molecule dopants. In this work, all-polymer n-type thermoelectric is reported by dissolving a novel n-type conjugated polymer and a polymer dopant, poly(ethyleneimine) (PEI), in alcohol solution, followed by spin-coating to give polymer host/polymer dopant blend film. To this end, an alcohol-soluble n-type conjugated polymer is developed by attaching polar and branched oligo (ethylene glycol) (OEG) side chains to a cyano-substituted poly(thiophene-alt-co-thiazole) main chain. The main chain results in the n-type property and the OEG side chain leads to the solubility in hexafluorineisopropanol (HFIP). In the polymer host/polymer dopant blend film, the Coulombic interaction between the dopant counterions and the negatively charged polymer chains is reduced and the ordered stacking of the polymer host is preserved. As a result, the polymer host/polymer dopant blend exhibits the power factor of 36.9 µW m^-1 K^-1, which is one time higher than that of the control polymer host/small molecule dopant blend. Moreover, the polymer host/polymer dopant blend shows much better thermal stability than the control polymer host/small molecule dopant blend. This research demonstrates the high performance and excellent stability of all-polymer n-type thermoelectric.