Photonic Crystal Selective Structures for Solar Thermophotovoltaics
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Photonic Crystal Selective Structures for Solar Thermophotovoltaics Zhiguang Zhou1, Enas Sakr1, Omar Yehia2, Anubha Mathur1, and Peter Bermel1 1 Purdue University, School of Electrical & Computer Engineering, 1205 W State St., West Lafayette, Indiana, USA, 47907 2 Purdue University, School of Mechanical Engineering, 585 Purdue Mall, West Lafayette, Indiana, USA, 47907 ABSTRACT Solar thermophotovoltaic (STPV) systems convert sunlight into electricity via thermal radiation. The efficiency of this process depends critically on both the selective absorber and the selective emitter, which are controlled by both the materials and the photonic design. For high concentration solar TPV applications, 2D photonic crystals (PhCs) made of refractory metals such as tungsten have demonstrated promising results. For even higher performance, we propose two photonic crystal-based designs to both collect solar heat and reradiate above-gap photons. First, a PhC selective structure (IPSS), which combines 2D photonic crystals and filters into a single device. Second, an Er-Yb-Tm co-doped fused silica coated with a 17-bilayer structure also offers significant selectivity with greater ease of fabrication. Finite difference time domain (FDTD) and rigorous coupled wave analysis (RCWA) simulations show that both can significantly suppress sub-bandgap photons. This increases sunlight-to-electricity conversion for photonic crystal-based emitters above 24.3% at 100 suns concentration or 27% at 1000 suns concentration using a Ga0.42In0.58As PV diode with a bandgap of 0.7 eV (nearly lattice-matched to InP). INTRODUCTION Solar thermophotovoltaic (STPV) systems convert sunlight into electricity via thermal radiation. The efficiency of STPV depends on the product of the selective absorber thermal transfer efficiency1 and the TPV system2, which are controlled by both the materials and the photonic design. Metal-dielectric composites like cermets3 and semiconductor-metal tandem4 are strong candidates for operation of conditions such as 100 suns concentration and 1000 K. It is also demonstrated that with proper design and fabrication, single wall carbon nanotubes exhibit selective absorption as well5. For artificial photonic structures, plasmonic selective absorbers6 were proposed due to its surface plasmon enhanced absorption. Photonic crystals made of refractory metals7 were proposed to be highly efficient selective solar absorbers under high temperature ( ) and high concentrations ( )8–10. Nevertheless, it is still challenging to design a selective solar absorber that has high efficiencies at high temperatures ( ) and moderate solar concentrations ( ) for the highest performance and potential for integration with the overall STPV system. One key challenge is that blackbody radiation at such high temperatures has strong overlap with the solar irradiance, making it extremely challenging to suppress thermal re-radiation while maintaining solar absorption. From a materials perspective, system integration may be facilitated by the use of similar materials
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