What To Expect from Conducting Polymers on the Playground of Thermoelectricity: Lessons Learned from Four High-Mobility Polymeric Semiconductors

Modification of the electronic structures of two benchmark donor–acceptor (D–A) copolymers poly­[(4,4′-bis­(2-ethylhexyl)­dithieno­[3,2-<i>b</i>:2′,3′-<i>d</i>]­silole)-2,6-diyl-<i>alt</i>-(2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT) and poly­[{2,5-bis­(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo­[3,4-<i>c</i>]­pyrrole-1,4-diyl}-<i>alt</i>-{[2,2′:5′,2″-terthiophene]-5,5″-diyl}] (PDPP3T) by chemical doping is reported. Simply by dipping polymer films into dopant solution, high electrical conductivity is achieved and thermoelectric property of the films is optimized. Despite their deep HOMO levels, optical absorption extending continuously to 2000 nm is observed in PSBTBT, and a high power factor around 25 μW m^–1 K^–2 is obtained in PDPP3T. Furthermore, temperature-dependent measurement of electrical conductivity and Seebeck coefficients is carried out to understand transport mechanisms and energetic distribution of carrier density of states (DOS). In parallel, doping treatment and corresponding characterizations are performed on donor polymers poly­(3-hexylthiophene) (P3HT) and poly­(2,5-bis­(3-dodecylthiophen-2-yl)­thieno­[3,2-<i>b</i>]­thiophene) (PBTTT-C12) for comparison. Ultimately, based on comprehensive characterizations and comparisons of the four polymers in terms of bulk mobility, DOS, film microstructures, and molecular structures, etc., a primitive correlation between solution-processable polymeric semiconductors and thermoelectric properties of their doped products is established