Thermophotonics: a means for overcoming limitations of thermophotovoltaics?

Thermophotonics (TPX) is a recently proposed concept, which generalizes Thermophotovoltaics (TPV) by allowing radiation from a heat source to be increased by an internal electrochemical potential difference. This paper examines the basic working principle of TPX by means of idealized detailed balance calculations. We show that the high (´superthermal´) power densities achievable by TPX allow for a sufficiently high external quantum efficiency a much higher rate of electrical power extraction from a heat source than TPV. Furthermore we show that for realistic geometries of the intermediate absorber the purely thermal power density of TPV limits the solar energy conversion efficiency, particularly for the conversion of concentrated sunlight. As a consequence of the superthermal power densities achievable by TPX solar energy conversion by TPX can achieve, in principle, higher efficiencies than TPV. Due to the increased power density the efficiency of solar TPX can even for realistic geometries of the intermediate absorber approach the thermodynamic solar energy conversion limits. An essential requirement, however, is very high external electro-luminescent quantum efficiency.