New development of one-dimensional Si/SiO2 photonic crystals filter for thermophotovoltaic applications

One-dimensional (1D) Si/SiO2 photonic crystals (PhCs) are regarded as the most promising candidates for thermophotovoltaic (TPV) optical filters. The performance of TPV devices can be significant improved with the designed 1D ten-layer Si/SiO2 PhC of excellent stop-band characteristic. However, large oscillations around 1.45–1.75μm in the pass band of this PhC filter would reduce the above band-gap power transmitted to the cells, leading to discounts of the system efficiency and power density. This work focused on the pass-band characteristics of the 1D Si/SiO2 PhCs. The mechanism of the large oscillations mentioned above was discussed and a modified 1D five-unit Si/SiO2 PhC in which the first and fifth units serve as refractive index match units to smooth the large oscillations in the pass band was presented. The simulation indicated that the modified 1D PhC exhibited much flatter and lower pass band around 1.45–1.75μm than that of the original 1D PhC, even for large incident angle of 45° for both TM and TE polarizations. Both PhCs in the modified and original structures were prepared through a magnetron sputtering process and the measured optical characteristics showed good coherence with the simulation results. An ideal thermodynamic model was then applied to predict the improvement of the TPV system performance by utilizing the modified 1D PhC filter. The results indicated that the modified 1D PhC would lead to 21.0–5.9% increase of the spectral efficiency and 14.8–5.3% increase of the power density at 1200–1800K radiator temperature.