Critical Design Parameters for Omnidirectional 2-D Filled Photonic Crystal Selective Emitter for Thermophotovoltaics

Thermophotovoltaic (TPV) systems are promising as small-scale, portable generators to power sensors, small robotic platforms, and portable computational and communication equipment. In TPV systems, an emitter at high-temperature emits radiation that is then converted to electricity by a low bandgap photovoltaic cell. One approach to improve the efficiency is to use hafnia-filled two-dimensional (2-D) tantalum (Ta) photonic crystals (PhCs). These emitters enable efficient spectral tailoring of thermal radiation for a wide range of incidence angles. However, fabricating these PhCs is difficult. We use focused ion beam (FIB) imaging and simulations to investigate the effects of fabrication imperfections on the emit- tance of a fabricated hafnia-filled PhC and to identify design parameters critical to the overall PhC performance. We demonstrate that, more so than uniform cavity filling, the PhC performance relies on the precise cavity period and radius values and thickness of the top hafnia layer.