Microfabricated silicon carbide thermionic energy converter for solar electricity generation

Abstract

This paper reports an initial prototype for microfabricated silicon carbide (SiC) thermionic energy converters (TECs), which have promise as topping stages for solar thermal electricity generation. Our initial TEC device achieved cathode temperatures of over 2000 K with incident optical intensity of approximately 1 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (equivalent to 1000 Suns), remained structurally stable under thermal cycling, and maintained a temperature difference between the cathode and the anode of over 1000 K. In addition, our device converted the estimated 0.1 W of optical power incident on the cathode to 0.12 nW of electrical power. The low conversion efficiency is due to the high work function of SiC, which severely limits the thermionic current. According to the Richardson-Dushman equation, the thermionic current should increase by more than six orders of magnitude if we cesiate both electrodes of the converter, increasing the efficiency accordingly. In our initial experiments, the thermionic current was enhanced by ~1.5 orders of magnitude using the cesium coating.