Efficient Solution-Processed n-Type Small-Molecule Thermoelectric Materials Achieved by Precisely Regulating Energy Level of Organic Dopants.

To achieve efficient n-type doping, three dopants, 2-Cyc-DMBI-H, (2-Cyc-DMBI)2 , and (2-Cyc-DMBI-Me)2 , with precisely regulated electron-donating ability were designed and synthesized. By doping with a small-molecule 2DQTT-o-OD with high electron mobility, an unexpectedly high power factor of 33.3 μW m-1 K-2 was obtained with the new dopant (2-Cyc-DMBI-Me)2 . Notably, with the intrinsically low lateral thermal conductivity of 0.28 W m-1 K-1 , the figure of merit was determined to be 0.02 at room temperature. Thus, we have demonstrated that small molecules with high electron mobility and low-lying LUMO energy levels can achieve high doping efficiency and excellent thermoelectric properties by doping with n-type dopants featuring highly matched energy levels and excellent miscibility.