Power optimization in thermionic devices

Conventional thermionic power generators and refrigerators utilize a barrier in the direction of transport to selectively transmit high-energy electrons, resulting in an energy spectrum of electrons that is not optimal for high efficiency or high power. Here, we derive the ideal energy spectrum for achieving maximum power in thermionic refrigerators and power generators. By using energy barriers that block or transmit electrons according to their total momentum rather than their momentum in the direction of transport, the power of thermionic devices can, in principle, be doubled and the electronic efficiency improved by 25%. Thermionic power generators [1] utilize a temperature difference between two reservoirs of electrons to transport high-energy electrons against an electrochemical potential gradient. By increasing the applied voltage between the reservoirs, the same device can operate in reverse as