Regulating the thermoelectric power factor of donor-acceptor copolymers by heavy chalcogen substitution: a first-principles study

The impact of heavy chalcogens with different sizes on the thermoelectric (TE) transport properties of polymers is still unclear. By replacing S with Se and Te, the effects of heavy chalcogens on TE transport properties along the intra-chain direction of PzDPP-based donor-acceptor (D-A) copolymers were investigated using first-principles calculations. The results show that the introduction of heavy chalcogens helps further weaken the D-A character of the copolymers, which can promote electron delocalization over the entire backbone, thereby improving the n-type doping efficiency. Besides, heavy chalcogens can reduce the effective mass and enhance the super-exchange coupling of holes and electrons. However, they have the opposite effect on the hole and electron scattering intensity, which increases the relaxation time of electrons significantly but decreases that of holes slightly. Finally, the substitution of Te can remarkably improve the n-type power factor, while introducing Se can enhance both n-type and p-type power factors. Our work reveals that the incorporation of heavy chalcogens is an effective strategy to improve the n-type TE transport properties of organic copolymers. Te substitution of sulfur (S) in PzDPP-based donor-acceptor copolymers enhances n-type power factor, while Se boosts both n-type and p-type power factors. Heavy chalcogen doping strategy shows promise for improving thermoelectric properties.