Metallic Photonic Crystal Absorber‐Emitter for Efficient Spectral Control in High‐Temperature Solar Thermophotovoltaics

A high-temperature stable solar absorber based on a metallic 2D photonic crystal (PhC) with high and tunable spectral selectivity is demonstrated and optimized for a range of operating temperatures and irradiances. In particular, a PhC absorber with solar absorptance (alpha) over bar = 0.86 and thermal emittance (epsilon) over bar = 0.26 at 1000 K, using high-temperature material properties, is achieved resulting in a thermal transfer efficiency more than 50% higher than that of a blackbody absorber. Furthermore, an integrated double-sided 2D PhC absorber/emitter pair is demonstrated for a high-performance solar thermophotovoltaic (STPV) system. The 2D PhC absorber/emitter is fabricated on a double-side polished tantalum substrate, characterized, and tested in an experimental STPV setup along with a flat Ta absorber and a nearly blackbody absorber composed of an array of multiwalled carbon nanotubes (MWNTs). At an irradiance of 130 kW m(-2) the PhC absorber enables more than a two-fold improvement in measured STPV system efficiency (3.74%) relative to the nearly blackbody absorber (1.60%) and higher efficiencies are expected with increasing operating temperature. These experimental results show unprecedented high efficiency, demonstrating the importance of the high selectivity of the 2D PhC absorber and emitter for high-temperature energy conversion.