  This article proposes a new energy harvesting concept that greatly enhances
thermionic power generation with high e ciency by exploiting the near- field
enhancement of thermal radiation. The proposed near-field enhanced thermionic
energy conversion (NETEC) system is uniquely configured with a low-bandgap
semiconductor cathode separated from a thermal emitter with a subwavelength gap
distance, such that a significant amount of electrons can be photoexcited by
near-field thermal radiation to contribute to the enhancement of thermionic
current density. We theoretically demonstrate that the NETEC system can
generate electric power at a significantly lower temperature than the standard
thermionic generator, and the energy conver- sion e ciency can exceed 40%. The
obtained results reveal that near-field photoexcitation can enhance the
thermionic power output by more than 10 times, making this hybrid system
attractive for renewable energy recycling.
