Thermoelectric and thermionic microgenerators: chances, challenges and limitations

This paper considers thermoelectric and thermionic converters - also in micro- and nanometer design - for power generation and cooling applications. The potential of thermionic converters is investigated precisely by a new advanced theory with inclusion of backward currents from the 2nd electrode and losses due to thermal radiation and ohmic resistance in the electrodes. The efficiency of thermionic converters is by far higher than for thermoelectric devices (including nanostructured superlattices) for high operating temperatures above 800degK, where efficiencies near Carnot can be obtained. Similar high efficiencies at low temperatures (ap 400degK) could only be achieved by electrode materials with reduced workfunction of about 0.3 to 0.5 eV