Metamaterial Thermal Emitters Based on Nanowire Cavities for High-Efficiency Thermophotovoltaics

Metamaterial thermal emitters based on gold nanowire cavities on a gold substrate are designed to achieve a narrowband emission spectrum with the emission peak located slightly above the bandgap of photovoltaic (PV) cells, in order to improve the overall efficiency of thermophotovoltaic (TPV) systems. The metamaterial emitter made of gold nanowires embedded in an alumina host exhibits an effective permittivity with extreme anisotropy, which supports cavity resonant modes of both electric dipole and magnetic dipole. The impedance match between the cavity modes and free space leads to strong thermal emission with the desired frequency range slightly above the bandgap of PV cells. Simulation results show that the designed metamaterial emitters are polarization-insensitive and have nearly omnidirectional emission angles. Moreover, theoretical analysis predicts that the overall efficiency of the TPV system can reach Shockley-Queisser limit at a low emitter temperature of T e = 940 K. © 2014 IOP Publishing Ltd