Applied Physics Seminar

Thermionic emission has long been an attractive idea for thermal energy conversion for its potentially high-efficiency conversion with no moving parts and simple device geometry. However, previous generations of convertors have had relatively poor actual performance due space charge effects and low output voltages, which has severely restricted their implementation and research. Here we discuss why modern microfabrication techniques and a new idea that combines both photovoltaic and thermionic effects together may reverse the fortunes of this technology, and lead to highly efficient conversion devices. We show that both theoretical and experimental data on MEMs thermionic devices show higher maximum currents than previously possible. Solar thermal applications also have a considerable quantity of light present, and we describe a new mechanism, photon-enhanced thermionic emission (PETE), that can benefit from both photon illumination and thermal energy. This process enables thermionic emission at much lower temperatures (~400ºC) than conventional thermionic emission, and may have higher overall efficiency. We will discuss experimental demonstrations of this process and the critical barriers to making lab prototypes into realistic conversion systems.