Benzothienobenzothiophene‐Based Organic Charge Transfer Complex and Carbon Nanotube Composites for p‐Type and n‐Type Thermoelectric Materials and Generators

Organic charge transfer complexes (CTCs) or electron donor–acceptor complexes have been intensively studied as organic semiconductors or organic conductors in organic electronics. Herein, the composite of CTCs and single‐walled carbon nanotubes (SWCNTs) is studied as both p‐type and n‐type thermoelectric materials for flexible thermoelectric generators. CTCs are formed by [1]benzothieno[3,2‐b][1]benzothiophene (BTBT) derivatives with different side chains as electron donors and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) as electron acceptors. The thermoelectric properties of the composites as well as the effect of side chains in BTBT derivatives are investigated. It is found that the PhBTBT–F4TCNQ/SWCNT composite film shows the highest p‐type power factor of 244.3 µW m−1 K−2; while the C8BTBT–F4TCNQ/SWCNT composite film exhibits the highest n‐type power factor of 105.1 µW m−1 K−2. The thermoelectric module based on five p–n junctions of C8BTBT–F4TCNQ/SWCNT exhibits the highest output voltage of 13.1 mV and output power of 340 nW under a 38 K temperature gradient. This device performance is mainly generated from the moderate carrier concentrations and low film defects in the n‐type C8BTBT–F4TCNQ/SWCNT composite film. Organic charge transfer complexes (CTCs) and single‐walled carbon nanotube (SWCNT) composites are used for both p‐type and n‐type organic thermoelectric materials and generators. CTC/SWCNT composite with alkyl side chains enables the highest output voltage of 13.1 mV and output power of 340 nW under a temperature gradient of 38 K.