Photonics roadmap for ultra-high-temperature thermophotovoltaics

The ability to control thermal emission is crucial for the thermal regulation of devices, barrier coatings, and thermophotovoltaic (TPV) systems. However, only a limited number of naturally occurring materials are stable at high temperatures (>1,800°C), and their emission spectra are set a priori by their intrinsic optical properties. Optical structures involving nanoscale textures can result in tunable emission spectra, albeit stable only at much lower temperatures. Here, we present an alternative approach that enables temperatures beyond 1,800°C through a bilayer stack achieved by combining the optical and thermal properties of 2,809 coating/substrate pairs. By varying the film thickness, we tailor the emission spectrum to create high-temperature, stable emitters. We illustrate this effect in combination with the most common TPV systems (GaSb, Ge, InGaAs, and InGaAsSb), showing power conversion efficiencies approaching 50% and power outputs as high as 10.2 W cm⁻². These concepts can be expanded to other high-temperature photonic applications for the spectral control of thermal emission.