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A naphthalene diimide (NDI)-based small molecule with a thienothiophene linker (NDI-TT-NDI) was synthesized for use as a semiconductor layer in solution-processable n-type organic field-effect transistors (OFETs). The thienothiophene linker was introduced to the donor site between the two NDIs to impart planarity to the molecular backbone, which is favorable for inducing high crystallinity, and the morphological and crystal characteristics of the resulting film were analyzed. An additional annealing treatment applied to the NDT-TT-NDI films changed their orientation such that the molecular ordering and crystallinity of the film were significantly improved at a specific annealing temperature. The optimally annealed NDI-TT-NDI film exhibited a distinct edge-on molecular orientation with a narrow intermolecular π−π stacking distance, which is advantageous for lateral charge transport along the stacks. Consequently, an optimally annealed NDI-TT-NDI-based OFET exhibited electron mobilities of up to 0.032 cm2V−1s−1 and an on/off ratio of 1.0 × 107. [ABSTRACT FROM AUTHOR]

The design of a conjugated polymer backbone influences the charge transport and doping efficiency; however, the construction of the polymer backbone for maximized thermoelectric performance is still unclear. Herein, a novel synthesis of a donor-acceptor (D-A) conjugated polymer with an extended planar backbone, C6-ICPDPP, is reported for the investigation of the thermoelectric behavior. The C6-ICPDPP comprises a combination of fused heterocyclic compounds, both electron donor and acceptor groups, which show p-doping characteristics with FeCl3 owing to the excellent planarization. The C6-ICPDPP films are formed from two types of solvents with different boiling points, both of which are doped with FeCl3, showing good thermoelectric properties; however, the thin-film structure, dopant diffusion, and thickness of the C6-ICPDPP films were different between the two solvents. With an increase in the doping concentration of FeCl3, the polarity of the majority charge carriers changes from positive to negative, indicating that the C6-ICPDPP exhibits both p- and n-type electrical behaviors with FeCl3 doping. The optimized power factors are 1.32 µW/mK2 (p-type) and 0.410 µW/mK2 (n-type), respectively, which are consistent with the change in the polaronic features at the given FeCl3 doping concentration. This study provides a design strategy for D-A conjugated polymers with extended planarization and electrical behavior suitable for organic thermoelectrics. [ABSTRACT FROM AUTHOR]