Single Ether-Based Side Chains in Conjugated Polymers: Toward Power Factors of 2.9 mW m^-1 K^-2

Combining side chain engineering and controlled alignment of PBTTT is an effective strategy to produce oriented thin films with improved thermoelectric performance when doped sequentially with the acceptor molecule hexafluoro-tetracyanonaphthoquinodimethane (F(6)TCNNQ). The substitution of linear alkyl side-chains (n-C-12) with a chain of identical length including an ether function (n-C7OC4) leads to a new class of slightly polar PBTTT polymers, preserving the ease of synthesis and air stability of alkylated PBTTTs. This side-chain modification improves the structural order of PBTTT backbones and the thermo-mechanical properties of the polymer. It then can be oriented by high temperature rubbing up to 240 degrees C to reach very high dichroic ratios up to 20 thanks to enhanced cohesive forces within side-chain layers. The side chain polarity of n-C7OC4 helps to tune the polymer-dopant interactions. A multi-technique approach demonstrates that F(6)TCNNQ dopants are randomly oriented in the disordered side chain layers of n-C7OC4 with some evidence of dopant clustering. The combination of improved alignment and random orientation of intercalated F(6)TCNNQ dopants helps reach a very high charge conductivity sigma = 5 . 10(4) S cm(-1) and a record power factor of 2.9 mW m(-1) K-2 in the polymer chain direction.