Acetal-Functionalized Indacenodithiophene (IDT): Controlling the Position of a Lewis Acidic Dopant for Improved Thermoelectricity

Novel acetal-functionalized indacenodithiophene (IDT) moieties were developed in this study. Conductive polymers containing IDT units are promising candidates for synthesizing high-performance thermoelectric materials because their high charge-carrier mobility in the amorphous state has the potential to reduce the thermal conductivity without affecting its electric conductivity. Nevertheless, IDT-containing polymers such as poly(indacenodithiophene- co -3,4-ethylenedioxythiophene) (PIDT-EDOT) exhibit poor conductivity (0.43 S cm –1 ). Herein, we propose a novel strategy to control the dopant position near the benzylic position of the polymer backbone via a Lewis acid–base complex between a novel acetal-functionalized IDT (IDTa) unit and a dopant, nitrosyl hexafluorophosphate. The PIDTa-EDOT polymer exhibited an increase in doping efficiency and condensed π–π stacking, which increased its electrical conductivity. Moreover, PIDTa-EDOT exhibited a considerably lower thermal conductivity (0.09 W m –1 K –1 ) than that exhibited by PEDOT:PSS (0.16–0.39 W m –1 K –1 ). This was because of the reduced grain size of the polymer post doping. Consequently, PIDTa-EDOT exhibited an ∼30-fold increase in electrical conductivity (12.56 S cm –1 ) and an ∼6-fold increase in thermoelectric performance (ZT = 7.57 × 10 –3 ) compared to those exhibited by PIDT-EDOT. Our research offers a new approach to increase electrical conductivity and decrease thermal conductivity simultaneously. This ultimately leads to the development of a high-performance thermoelectric material.