Thermal transport theory of organic semiconductors

Organic semiconductors (OCSs) have very recently received much attentions as potential thermoelectric materials, originating from the fact that they are both semiconducting and that they exhibit relatively low thermal conductivity than that of inorganic materials. The low thermal conductivity of OCSs can remarkably increase the energy conversion efficiency. Generally, thermal transport in OCSs fundamentally differs from that in inorganic materials and is determined by the charge carriers and phonons in localized states. Understanding thermal transport performance of OCSs is important for a fundamental description of energy flow and then a better design of organic thermoelectric devices. We present a unified theoretical model to describe the thermal transport performance of the OCSs based on hopping transport theory. The proposed model predicts that the contribution from phonon to the thermal conductivity is larger than that from charge carrier in the OCSs. Moreover, the proposed model can well interpret the thermal transport feature of the OCSs by combining the disorder, temperature, and carrier concentration. Simulation results imply that thermal conductivity in the OCSs could be strongly affected under large electric field, high carrier and dopant concentration.