High Spectral Selectivity of Tantalum Cross-Shaped Unit Elements for STPV Systems

The efficiency of single-junction PhotoVoltaic (PV) cells is restricted by the Shockley-Queisser (SQ) limit. This work presents a simulation based design of metasurface absorber and emitter for Solar ThermoPhotoVoltaics (STPV) system that overcomes the SQ limit by employing Tantalum resonators which exhibits high spectral selectivity. The STPV system introduces an intermediate structure consisting of a broadband optical absorber and a selective emitter before solar radiations reach PV cell. The operating temperature of the system being very high, a refractory metal Tantalum (Ta) with a melting point of 3017 °C provides high thermal stability. Metasurface broadband Ta-based absorber design is a supercell consisting of four cross resonators with total thickness of 290 nm. The absorber design gives broadband absorptance for 200–2000 nm region, which efficiently covers ultraviolet, optical, and infrared regimes. The absorber has an efficiency of is 91.5%, and 91.9% for BBR, and for the air mass (AM) 1.5 spectrum, respectively. On the contrary, emitter employs a unit element in the shape of a cross with a total thickness of 272 nm. The emitter of proposed intermediate design achieves high spectral selectivity for targeted quaternary PV cell InGaAsSb having a bandgap of 0.55 eV through narrowband emittance. The maximum simulated STPV efficiency attained by design is 39.1% considering polarization and angle-insensitivity of the design.