Enhancing thermoelectric efficiency of benzodithiophene-thienothiophene copolymers through doping-induced charge transfer

Abstract

Organic thermoelectric materials have been gaining increasing interest due to their capacity to convert waste heat into electricity. This study explores the impact of doping-induced charge transfer states on the thermoelectric properties of benzodithiophene-thieno[3,2-b]thiophene-based polymers (PBDTTT) doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Detailed structural, optical, and electrical analyses were conducted on two specific polymers, PBDTTT:C (P1) and PBDTTT:EFT (P2). The investigation revealed distinct doping behaviors: P1 formed a partial charge transfer (PCT) complex, whereas P2 predominantly formed an integer charge transfer (ICT) complex. This distinction is attributed to the inherent structural differences and varying aggregation capabilities of the polymers. As a result, P2 exhibited enhanced electrical conductivity and a superior thermoelectric power factor compared to P1. This study emphasizes the critical role of polymer aggregation and charge-transfer mechanisms in optimizing the thermoelectric performance of conjugated polymers. It offers valuable insights for the development of efficient thermoelectric materials and the advancement of energy conversion technologies.