Over the last several decades, there has been a dramatic progress
in the development of green energy technology which can
reduce greenhouse gas emissions and fossil fuel usage. Thermoelectric
(TE) devices, which consist of p-type and n-type semiconductors,
can be considered as a useful tool to practice the green
energy technology. TE devices can be divided into two types,
namely thermoelectric coolers (TECs) [1e4] and thermoelectric
generators (TEGs) [5e8]. TECs convert electricity into thermal
energy for cooling via the Peltier effect, whereas, TEGs convert
thermal energy, say, waste heat, into electrical power via the Seebeck
effect.