Abstract
Hafnia-filled, two dimensional (2D) tantalum (Ta) photonic crystals (PhCs) are promising emitters for high performance thermophotovoltaic (TPV) systems because they enable, for a wide range of incidence angles, efficient spectral tailoring of thermal radiation. However, fabricating these PhCs to the required tolerances has proven to be a challenging task. In this paper, we use both focused ion beam (FIB) imaging and simulations to investigate the effects of fabrication imperfections on the emittance of a fabricated hafnia-filled PhC and to identify critical geometric features that drive the overall PhC performance. We demonstrate that, more so than uniform cavity filling, the key to the best filled PhC performance is the precise cavity period and radius values and thickness of the top hafnia layer.
Highlights
Thermophotovoltaic (TPV) systems are promising as small scale, portable generators to power small robotic platforms, sensors, and portable computational and communication equipment
In TPV systems, thermal radiation from an emitter at high temperature is converted to electricity by a low bandgap photovoltaic (PV) cell
A key factor for the system efficiency is the ratio of in-band emissivity—convertible by the PV cell—relative to the total emissivity
Summary
Thermophotovoltaic (TPV) systems are promising as small scale, portable generators to power small robotic platforms, sensors, and portable computational and communication equipment. Filled PhCs are difficult to fabricate, largely because the cavity period a and radius r are reduced by approximately half (compared to the coated PhC) due to hafnia’s high index of refraction (∼2).
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