Numerical investigation of tandem photonic crystal filters for thermophotovoltaic applications

Two-dimensional photonic crystals (2D PhCs) select photons by cavity resonance, and can be used to design selective filters for thermophotovoltaic (TPV) applications. Due to the broad pass band and high out-band reflectance of the 2D PhC structure, the TPV system can achieve both high power density and high efficiency. However, the absorption during cavity resonance restrains the further improvement of performance. In this article, a 2D metallic PhC layer was added on top of a one-dimensional photonic crystal filter, and the best geometric parameters were obtained. The simulation indicated that the parasitic absorption of the optimized tandem photonic crystal filter can be reduced to half of the traditional metallic 2D PhC filters. The new filter also shows a sharper cut-off edge and better in-band transmittance. Moreover, an ideal thermodynamic model was applied to estimate the performance of TPV systems with a filter. Using a 1200 C blackbody emitter, the spectral efficiency of the tandem photonic crystal filter can reach 73%, and the in-band transmittance is over 80%. When optimizing the filter based on existing GaSb cells, the system power conversion efficiency can reach 28%.