Realizing Ultralow Energetic Disorder and High Thermoelectric Performances via Nanoscale Polymer Packing Control.

Abstract

Charge transport and thermoelectric (TE) properties of conjugated polymers are largely determined by their solid-state energetic disorders. Previous studies have focused on the energetic disorders or traps that result from dihedral angle rotations of the polymer backbone. However, this fails to explain the largely different charge transport properties in many conjugated polymers. Here, we investigate the charge transport and TE properties of two isomeric polymers with highly rigid backbones and low energetic disorders along the chain. Both polymers have similar ultralow charge transport activation energies (<35 meV), but exhibit vastly different charge transport properties. We found that P(PzDPP-Pz) with a linear backbone exhibited a high n-type TE power factor, over 2 orders of magnitude higher than its isomer P(PzDPP-Dz). By utilizing multiple characterizations and molecular simulations, we, for the first time, rule out the well-known dihedral-angle rotation disorders and unveil that the disorders and traps originate from the nanoscale polymer packing structures. Our work provides insight into the origins of the various types of disorders and traps across multilevel nanoscale structures in polymer semiconductors.