High Power Density Thermionic Energy Conversion Using Nanostructured Electron Optical Grids

Solid state thermionic generators offer a promising route towards highly efficient, direct heat-to-electricity conversion, but their performance has historically been limited by space charge accumulation within the vacuum gap of the converter. Recent approaches to mitigating space charge using positively biased electrostatic grids have suffered from intrinsic efficiency limits arising from grid loss. Here, we describe the successful design, computational modeling, and experimental realization of a nanostructured electrostatic lensing system which accelerates thermionically emitted electrons across the vacuum gap while minimizing grid loss. Using kinetic particle-in-cell electron dynamics simulations, we computationally designed a panel of collector devices with significant enhancements in predicted power density and electronic efficiency over conventional diode converters. The devices were fabricated on semiconductor substrates and characterized in ultra-high vacuum experiments under a Ba dispenser cathode. We report experimental grid loss measurements for these devices, as well as quantitative agreement between simulation predictions and experimental results over a wide range of device configurations.