Recently, near-field radiative heat transfer enhancement across nanometervacuum gaps has been intensively studied between two hyperbolic metamaterials(HMMs) due to unlimited wavevectors and high photonic density of state. In thiswork, we theoretically analyze the energy conversion performance of athermophotovoltaic (TPV) cell made of In0.2Ga0.8Sb when paired with a HMMemitter composed of tungsten nanowire arrays embedded in Al2O3 host atnanometer vacuum gaps. Fluctuational electrodynamics integrated with effectivemedium theory and anisotropic thin-film optics is used to calculate thenear-field radiative heat transfer. It is found that the spectral radiativeenergy is enhanced by the epsilon-near-zero and hyperbolic modes at differentpolarizations. As a result, the power output from a semi-infinite TPV cell isimproved by 1.85 times with the nanowire HMM emitter over that with a plaintungsten emitter at a vacuum gap of 10 nm. Moreover, by using a thin TPV cellwith 10 um thickness, the conversion efficiency can be greatly improved from19.5% to 31.5% without affecting the power generation, due to the totalinternal reflection occurring at the bottom cell interface that minimizes thesub-bandgap spectral radiative energy. Furthermore, the effects of a TPV celland a nanowire emitter with finite thicknesses are also studied. The resultshows that the maximum efficiency of 32.2% is achieved with an optimal cellthickness of 3 um while the nanowire HMM emitter should be thick enough to beopaque. The fundamental understanding and insights obtained here willfacilitate the design and application of novel materials in enhancingnear-field TPV energy conversion.
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