Material candidates for thermally robust applications of selective thermophotovoltaic emitters

As the majority of the input energy in power generation or energy consumption processes goes to waste as heat, thermophotovoltaic (TPV) devices enable energy recovery from (waste) heat. In TPV devices, the power output and conversion efficiency are impacted by thermal emitters. Since TPV devices operate at higher temperatures, emitters that can withstand hot environments without significant degradation of their emission performance are required. Refractory metals are commonly used as the emitter material due to their higher melting point and optical properties. This paper reviews physical and chemical properties of 15 refractory metals that may affect the emitter's performance at high temperatures: melting point, crystal structure, lattice constant, standard reduction potential, diffusion coefficient, Young's modulus, thermal expansion coefficient, and refractive index. Biological hazards and prices of the metals are also explored. Then, selective TPV emitters fabricated with the refractory metals are compared regarding their thermal stability. Finally, material properties are discussed toward achieving thermally robust TPV emitters.