Balance of electrical conductivity and Seebeck coefficient by controlled interfacial doping towards high performance benzothienobenzothiophene-based organic thermoelectric materials

Herein, we demonstrated a new strategy of balancing the electrical conductivity and Seebeck coefficient for high-performance p-type organic thermoelectric composites of single-walled carbon nanotubes (SWCNTs) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8BTBT) by controlling the doping process. It was found that interfacial doping of the thermoelectric composite films with a vacuum-deposited organic acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), led to the formation of charge-transfer complex crystals at the interface, which resulted in higher carrier mobilities and moderate carrier concentrations compared with the solution-phase bulk doping method. The composite film of SWCNT/C8BTBT interfacial-doped with fine-tuned 40 nm-thick TCNQ exhibited a power factor as high as 284 μW m−1 K−2 at room temperature, which was five times higher than that of the bulk doped film for similar dopant addition. The high power factor of the interfacial-doped composite film was attributed to the less interruption to the lattice structure and controlled charge transfer processes among SWCNTs, C8BTBT and TCNQ. This strategy can be used as a general method for high-performance organic thermoelectric composites.