Enhanced thermoelectric properties through minority carriers blocking in nanocomposites

We use the Boltzmann transport equation under the relaxation time approximation to investigate the effect of minority blocking on the transport properties of nanocomposites (NCs). Taking p-type Bi 0.5Sb 1.5Te 3 NCs as an example, we find that the thermally excited minority carriers can be strongly scattered by engineered interfacial potential barriers. Such scattering phenomena suppress the bipolar effect, which is helpful to enhance the Seebeck coefficient and reduce the electronic thermal conductivity, especially at high temperatures. Further combining with the majority carriers low-energy filtering effect, the power factor and the figure of merit (ZT) can be significantly enhanced over a large temperature range from 300 K to 500 K. Such an improvement of ZT is attributed to the majority carriers low-energy filtering effect at low temperatures and to the minority carriers blocking effect at high temperatures. A principle that is helpful to provide guidance on the thermoelectric device design is identified: (1) blocking the minority carriers as often as possible and (2) filtering the majority carriers whose energy is lower than 2–3 k B T near the cold end.