Micro-gap thermo-photo-thermionics: An alternative approach to harvesting thermo-photons and its comparison with thermophotovoltaics

TL;DR

This study proposes a thermo-photo-thermionic device as an alternative to thermophotovoltaics for energy harvesting, demonstrating higher power density and efficiency through photon coupling and thermionic conversion.

Contribution

It introduces a novel thermo-photo-thermionic energy harvesting approach and compares its performance with traditional thermophotovoltaics using advanced theoretical analysis.

Findings

Thermo-photo-thermionic device achieves over twice the power density of thermophotovoltaics.

Energy conversion efficiency can be improved by more than 30% with the new device.

Maximum power point voltage exceeds the band gap of the conversion material.

Abstract

This work investigates an alternative to thermophotovoltaics for harvesting thermal and optical energy via photon coupling and thermionic energy conversion. In this device, a heat source is radiatively coupled to a thermionic electron emitter through a nanoscale gap and the electron emitter is coupled to collector through a microscale gap. The analysis using fluctuational electrodynamics and finite time thermodynamics shows that for identical thermal radiator and photon to electron conversion materials, the output power density in the thermionic device can be more than twice that of the thermophotovoltaic device; the thermionic mechanism can also provide more than 30 percent improvement in the energy conversion efficiency compared to the thermophotovoltaic device. Moreover, the maximum power point voltage in the thermionic device is shown to significantly exceed the band gap of conversion material, which determines the theoretical upper limit of the open circuit voltage in a thermophotovoltaic cell. Therefore, the results of this study indicate that thermionic energy harvesting via thermo-photon coupling can be a promising alternative to thermophotovoltaics.