A high-performance, metallodielectric 2D photonic crystal for thermophotovoltaics

Fuel-combustion-based thermophotovoltaic (TPV) systems are emerging as a viable power source for small, portable generators for a spectrum of applications such as UAVs, robotic platforms, and sensors. In TPV systems, an emitter heated to above 1000 K emits radiation that is then converted to electricity by a low bandgap photovoltaic cell. One promising class of TPV emitters are two-dimensional photonic crystals (PhCs) made of tantalum, which have shown high-temperature stability at 1150–1250K over hundreds of hours [1], [2] and have been implemented in a prototype system with 4.4% fuel-to-electricity efficiency [1]. Tantalum PhCs filled and capped with hafnium oxide can enable even higher optical performance with in-band emissivities of 0.8–0.9. However, two key features are difficult to realize simultaneously: a uniformly filled cavity and a thin capping layer of hafnium oxide [3], [4]. Here, we present a process that results in reduced roughness and better thickness control of the capping layer. We use room temperature reflectance measurements and full system simulations to estimate system performance gains. This selective emitter paves the way toward efficient, practical, and portable mesoscale generators.