Hot Electron Emission in Plasmonic Thermionic Converters

Thermionic converters generate electricity from thermal energy in a power cycle based on the vacuum emission of electrons. While thermodynamically efficient, practical implementations are limited by the extreme temperatures required for electron emission (>1500 K). Here we show how metal nanostructures that support resonant plasmonic absorption enable an alternative strategy. The high temperatures required for efficient vacuum emission can be maintained in a subpopulation of photoexcited hot electrons during steady-state optical illumination, whereas the lattice temperature of the metal remains within the range of thermal stability, below 600 K. We have also developed an optical thermometry technique based on anti-Stokes Raman spectroscopy that confirms these unique electron dynamics. Thermionic devices constructed from optimized plasmonic absorbers show performance that can outcompete other strategies of concentrated solar power conversion in terms of efficiency and thermal stability.