Manipulating Carrier Concentration by Self-Assembled Monolayers in Thermoelectric Polymer Thin Films

Conjugated polymers have attracted considerable attention for thermoelectric applications in recent years due to their plentiful resources, diverse structures, mechanical flexibility, and low thermal conductivity. Herein, we demonstrate a new strategy of modulating charge carrier concentration of chemical-doped polymer films by modifying the substrate with self-assembled monolayers (SAMs). The SAM with a trifluoromethyl terminal group is found to accumulate holes in the polymer thin films, while the SAM with an amino terminal group tends to donate electrons to the polymer films. Thermoelectric thin films of conjugated donor-acceptor copolymer exhibit high power factors of 55.6-61.0 μW m^-1 K^-2 on SAMs with polar terminal groups. These power factors are 49% higher than that on the SAM with the nonpolar terminal group and 3 times higher than that on pristine substrate. The high power factor is ascribed to the modulated charge carrier concentration and improved charge carrier mobility as induced by SAMs.