Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators

The impacts of radiative, electrical and thermal losses on the power output enhancement of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten emitter, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the absorption bandgap. In a nano-TPV power generator cooled by convection with a fluid at 293 K and a heat transfer coefficient of 10^4 Wm^-2K^-1, power output enhancements of 4.69 and 1.89 are obtained for the tungsten and Drude radiators, respectively, when a realistic vacuum gap thickness of 100 nm is considered. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output is determined. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.