Improving thermoelectric efficiency in organic-metal nanocomposites via extra-low thermal boundary conductance

In organic semiconductors, the Wiedemann-Franz law is often violated, potentially enabling independent control over electrical and thermal conductivities, as observed here with the organic-metal nanocomposites. This effect is attributed to the interface between metal particles and organic matrix materials impeding thermal transport. Thermal conductivity (kth) can be decoupled from electrical conductivity (σe) in the composite of an archetypal organic semiconductor (Copper Phthalocyanine, CuPc) and silver, with thermal boundary conductance as low as 13 MW/m2K at the interface. We show that kth decreases with volume fraction occupied by silver nanoparticles (xAg%) in the dilute limit, reaching a minimum value at a concentration xAg%(min)=18%, while σe exceeds that of the pure organic semiconductor. Further modeling indicates that ZT values of organic-inorganic nanocomposites can be potentially enhanced 10 fold around xf%(min), compared to ZT of the pure compounds. These findings suggest a novel pathway for the future design of organic thermoelectric materials.