  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.
