Isomers\nof n‑Type\nPoly(thiophene-<i>alt</i>-<i>co</i>-thiazole)\nfor Organic Thermoelectrics

n-Type polythiophene represents a\npromising category\nof n-type\npolymer thermoelectric materials known for their straightforward structure\nand scalable synthesis. However, n-type polythiophene often suffers\nfrom a twisted backbone and poor stacking property when introducing\nhigh-density electron-withdrawing groups for a lower lowest unoccupied\nmolecular orbital (LUMO) level, which is considered to be beneficial\nfor n-doping efficiency. Herein, we developed two isomers of polythiophene\nderivatives, PTTz1 and PTTz2, by inserting thiazole units into the\npolythiophene backbone composed of thieno[3,4-<i>c</i>]pyrrole-4,6-dione\n(TPD) and thiophene-3,4-dicarbonitrile (2CNT). Although PTTz1 and\nPTTz2 share a similar polymer skeleton, they differ in thiazole configuration,\nwith the nitrogen atoms of the thiazole units oriented toward TPD\nand 2CNT, respectively. The insertion of thiazole units significantly\nplanarizes the polythiophene backbone while largely preserving low\nLUMO levels. Notably, PTTz2 exhibits a more coplanar backbone and\ncloser π-stacking compared to PTTz1, resulting in a greatly\nenhanced electron mobility. Both PTTz1 and PTTz2 can be easily n-doped\ndue to their deep LUMO levels. PTTz2 demonstrates superior thermoelectric\nperformance, with an electrical conductivity of 50.3 S cm<sup>–1</sup> and a power factor of 23.8 μW m<sup>–1</sup> K<sup>–2</sup>, which is approximately double that of PTTz1. This\nstudy highlights the impact of the thiazole unit on n-type polythiophene\nderivatives and provides valuable guidelines for the design of high-performance\nn-type polymer thermoelectric materials.