Nanostructured Spacers for Thermionic and Thermophotovoltaic Energy Converters

Microgap thermionic energy converters and nanogap thermophotovoltaic devices can efficiently generate electricity from heat without using moving parts. However, converters that have diminutive spacings are difficult to operate and challenging to manufacture at scale. Previous efforts to establish small gaps, such as microfabricated pillars or nanobeads, have resulted in problems including excessive parasitic heat transfer and temperature limitations. To overcome these obstacles, we have developed a microfabricated spacer film that incorporates precisely positioned standoffs in order to limit the area available for conductive losses. We show that this film increases thermal resistance by more than 50% relative to previous designs and demonstrate its use in a thermionic converter to achieve a temperature difference of ~350 K over a gap of $\sim 2~\mu \text{m}$ across an area of ~1.25 cm2. These films will allow mass production of efficient, high-power-density solid-state electricity generators. [2020-0174]