Electron-withdrawing quinone polymers with enhanced conjugated planarity for n-type organic thermoelectrics

Abstract

The development of n-type conjugated polymers with superior thermoelectric properties remains a major challenge, primarily attributed to the limited availability of high-performance electron transport units. In this paper, two polymers, PBFDOTh-T and PBFDOTh-Se, are synthesized by introducing a 3,7-dihydrobenzo[1,2-b:4,5-b′]difuran-2,6-dione (BFDO)-derived structural unit featuring quinone resonance properties. Due to the strong electron-deficient effect of the BFDO unit, both polymers exhibited low-lying lowest unoccupied molecular orbital (LUMO) energy levels, which enabled an efficient n-doping procedure. Additionally, the introduction of the quinone unit effectively facilitated carrier delocalization, and both polymers achieved high electrical conductivities after n-doping, with the highest conductivity of 8.6 S cm⁻¹ obtained in the doped PBFDOTh-Se polymer. Detailed analysis revealed that the introduction of selenophene further enhanced the conjugated planarity of the polymer and reduced the structural disorder caused by doping, thus allowing a higher n-doping level and enabling simultaneous increases in conductivity and Seebeck coefficient. Finally, PBFDOTh-Se showed the highest power factor (PF) of 22.7 μW m⁻¹ K⁻². This work provides a way to construct high-performance n-type quinone polymers for thermoelectrics and offers insights into the relationship between polymer structure and thermoelectric properties.