Quantifying the performance of optical emitters in thermophotovoltaics with single- and dual-junction cells

Thermophotovoltaics (TPVs) convert radiation from an emitter to electricity using a photovoltaic (PV) cell. Through tuning of the optical properties of the emitter, the TPV system can be designed to achieve higher cell power densities and power conversion efficiencies. One methodology for achieving control over the emission spectrum is through subwavelength layers of thin film materials that can tune the emissivity as a function of wavelength. Here, we comprehensively analyze the use of a single coating layer on a bulk material to enhance both the power and efficiency achieved by the TPV system. We choose a pure Mo substrate, coated with a thin film of AlN, varying the coating thickness to tune the radiated spectrum. We quantify the gain in efficiency for PV cells of InGaP and InGaAsSb by moving from the pure Mo to an AlN coated emitter as a function of the film thickness, which when optimized improves the efficiency by ⪆5% over the substrate alone. In addition, we show how the bilayer, along with a tandem PV cell of InGaP and InGaAsSb can reach a theoretical efficiency of ⪆50% at 1,800°C. The methodology presented here can be extended to different emitter systems and tandem PV cells.