Thermoelectrics can convert low-grade heat into electricity is essential to meet the increasing demand for renewable energy systems. However, their heat-to-electricity conversion efficiency is governed by a material factor, thermoelectric figure of merit (ZT). ZT is limited by the tradeoff between thermal conductivity, electrical conductivity, and Seebeck coefficient, all of which are coupled. Taking thermoelectric material system into nanoscale composites is a common strategy to raise or tune the material-related term ZT. ZT is determined by thermal conductivity and power factor, which is product of square of Seebeck coefficient and electrical conductivity. Nanoscale composites inherently possess phonon scattering centers that can suppress thermal conductivity. Besides, two main power factor enhancement mechanisms were identified for nanoscale composite systems; (i) modulation doping and (ii) energy-dependent charge carrier scattering. In this paper, principles and reported examples of those two power factor improvement mechanisms will be outlined and summarized.
변조 도핑 (modulation doping)
전하 캐리어 산란 (energy-dependent charge carrier scattering)