Alcohol-Processable All-Polymer n-Type Thermoelectrics

XY Fan and J Liu and XZ Duan and HX Li and SH Deng and YZ Kuang and JY Li and CJ Lin and B Meng and JL Hu and SM Wang and J Liu and LX Wang, ADVANCED SCIENCE, 11 (2024).

DOI: 10.1002/advs.202401952

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 mu W 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. A high-performance n-type thermoelectric is developed by dissolving a new polymer host and a polymer dopant poly(ethyleneimine) (PEI) in hexafluoroisopropanol. The new combination reduces Coulombic interaction between the dopant counterions and the charged polymer chains, which leads to preserved ordered stacking of the polymer host. As a result, the Seebeck coefficient is enhanced and consequently higher power factor and improved thermal stability. image

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