Optical Structures for Thermophotovoltaic Emitters: Power Generation from Waste Heat

Abstract: Heat is an inevitable outcome in energy consumption processes, as more than 65% of input energy is wasted as heat. If we can generate electricity from waste heat, it will help minimize the needs for fossil fuels in power plants and can reduce carbon emissions. One way to generate power from heat is through the use of thermophotovoltaics (TPVs), where photons radiated from thermal emitters are converted into electricity. To optimize TPV performance, it is crucial to design emitters such that their emissivity spectrum matches their operating temperature. For example, higher emissivity is needed at shorter (longer) wavelengths at higher (lower) temperatures. Thus, having the ability to create wavelength-selective emitters can enable TPV applications for a wider range of temperatures. This research focuses on utilizing metamaterials (2D emitters) and planar thin films (1D emitters) to create those emitters. Simulation, fabrication, material property analysis, and radiation measurements were used to characterize the emitters. Based on simulation, metamaterial emitters exhibit engineerable emissivity due to various mechanisms of their optical resonance. Also, large-area fabrication of 1D emitters (78 cm2) was achieved owing to their simple structure, which is required to produce higher TPV power output. Incorporating the characteristics of emitters of each type, their advantages and challenges are discussed. Therefore, the comprehensive results of this research help realize practical implementation of TPV applications.