Design of tungsten complex gratings for thermophotovoltaic radiators

The concept of a kind of complex grating based on superposition of two simple binary gratings is described for potential application as thermophotovoltaic (TPV) radiators. The grating with one-dimensional microstructured surface is relatively easy to fabricate and the predicted directional-spectral emittance exhibits apparent enhancement over simple grating structures. Specifically, the emittance of the complex grating has a wider peak in the spectral region where the quantum efficiency of TPV cells is high. This enhancement can be explained by the excitation of surface plasmon polaritons coupled with the grating microstructures. At longer wavelengths, the emittance remains low to reduce the radiative heat transfer from the radiator to the TPV cells by low-energy photons that do not produce any photocurrent. Calculations using the rigorous coupled-wave analysis demonstrate that the emittance peak is insensitive to the direction, suggesting that the proposed structure may be well suitable for TPV applications.