Performance of near-field thermophotovoltaic cells enhanced with a backside reflector

Thermophotovoltaic (TPV) systems are very promising for waste heat recovery. This work analyzes the performance of a near-field TPV device with a gold reflecting layer on the backside of the cell. The radiative transfer from a tungsten radiator, at a temperature ranging from 1250 K to 2000 K, to an In_0.18Ga_0.82Sb TPV cell at 300 K is calculated using fluctuational electrodynamics. The current generation by the absorbed photon energy is modeled by the minority carrier diffusion equations considering recombination. The energy conversion efficiency of the cell is determined from the generated electrical power and the net absorbed radiant power per unit area. A parametric study of the cell efficiency considering the gap spacing and other parameters is conducted. For an emitter at temperature 1250 K, the efficiency enhancement by adding a mirror, which reduces the sub-bandgap radiation, is shown to be as much as 35% relative to a semi-infinite TPV cell. In addition, the potential for further improvement by reducing surface recombination velocity from that of a perfect ohmic contact is examined. The cell performance is shown to increase with decreasing gap spacing below a critical surface recombination velocity.