Backbone Effects on the Thermoelectric Properties of Ultra-Small Bandgap Conjugated Polymers

Conjugated polymers with narrower bandgaps usually induce higher carrier mobility, which is vital for the improved thermoelectric performance of polymeric materials. Herein, two indacenodithiophene (IDT) based donor–acceptor (D-A) conjugated polymers (PIDT-BBT and PIDTT-BBT) were designed and synthesized, both of which exhibited low-bandgaps. PIDTT-BBT showed a more planar backbone and carrier mobility that was two orders of magnitude higher (2.74 × 10 −2  cm 2 V −1 s −1 ) than that of PIDT-BBT (4.52 × 10 −4  cm 2 V −1 s −1 ). Both exhibited excellent thermoelectric performance after doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, where PIDTT-BBT exhibited a larger conductivity (0.181 S cm −1 ) and a higher power factor (1.861 μW m −1  K −2 ) due to its higher carrier mobility. The maximum power factor of PIDTT-BBT reached 4.04 μW m −1  K −2  at 382 K. It is believed that conjugated polymers with a low bandgap are promising in the field of organic thermoelectric materials.