The large-scale use of thermo-electrics for conversion of waste heat to electricity is currently limited by materials' cost and efficiency. The efficiency of a thermoelectric conversion is normally expressed through its figure of merit (zT=S 2sigmaT/kappa), where S is the Seebeck coefficient, sigma is the electrical conductivity, kappa is the thermal conductivity, and T is the absolute temperature. The key challenge in improving zT is the conflict dependence of the variables (S, sigma and kappa).

A strategy that could decouple the variables and thereby lead to an efficient and economical thermoelectric conversion is to fabricate nanoscaled hetero-structured materials through a large-scale and low-cost chemical route. In my research, two types of hetero-structures were demonstrated to have enhanced zT. The type I structure is a semiconductor matrix with mesoscaled pores. The pores are proved to substantially reduce kappa more than sigma by scattering the phonons at interfaces. In the type II structure, metallic Ag nanoparticles are homogeneously dispersed in a Sb2Te3 matrix using hydrazinium chemistry. After improving the thermal stability of Ag nanoinclusions in telluride by atomic layer deposition (ALD), a zT value of 1.0 at 460 K has been achieved, a record for a solution-processed film. This enhancement is mainly due to improvement of the Seebeck coefficient via a hot carrier filtering effect, along with the efficient scattering of phonons.

I believe that this new methodology will inspire the thermoelectric community in the development of improved thermoelectric systems.