Enhancing doping efficiency by improving host-dopant miscibility for fullerene-based n-type thermoelectrics

This paper describes a promising n-type doping system with high performance for thermoelectric applications. By introducing the polar triethylene glycol (TEG) side chain onto both fullerene host (PTEG1) and dopant (TEG-DMBI) materials, the TEG-DMBI doped PTEG-1 films obtained through solution processing provide a better miscibility compared with films doped with commercially available N-DMBI (bearing a dimethylamino group instead of TEG), as determined by phase imaging AFM (atomic force microscopy) measurements and coarse-grain molecular dynamics simulations, leading to high doping efficiency up to 18% at 20 mol% doping concentration and thus high carrier density and mobility, which are critical to the electrical conductivity. Therefore a record power factor of 19.1 mu W m(-1) K-2 is obtained with an electrical conductivity of 1.81 S cm(-1), one of the highest values reported for solution processable fullerene derivatives as n-type organic materials for thermoelectric applications to date.