Highly Efficient Solar Energy Conversion Using Graded-index Metamaterial Nanostructured Waveguide

In this paper, a graded-index metamaterial (GIM) nanostructured waveguide is proposed to enhance the performance of solar cells via a tunable absorption spectrum. The proposed four-layer nanostructured waveguide consists of two GIM and SiNx films which are squeezes between glass substrate and air. Using a transmission matrix method, the transmittances as well as the reflectance are calculated for different film thicknesses, refractive indices and incidence angles. We demonstrate that the reflectance is nearly zero where SiNx refractive index is 2.2 in vicinity of 620 nm. As the incident angle increases, the minimum reflectance wavelength blueshifts and slightly increase in the value. In addition, the variation in the minimum reflectance due to a change in the thickness of SiNx layer studied in detail. We show that the absorbance of a solar cell can be easily controlled by varying refractive index and/or thickness of SiNx layer in the proposed nanostructure. The result shows that the best efficiency occurs at normal incidence, n2 = 2.2, and d2 = 30 nm.

Band Gap Characteristics of Phononic Crystal Made from Different Material

The band gap characteristics of phononic crystal is influenced by material and structure etc. Based on the transmission matrix method, the first band gap characteristics of one-dimensional phononic crystal were numerical simulation with different ratio, and these phononic crystals were made form aluminum, lead, steel, carbon and epoxy resin materials. These results show that phononic crystal structure made from high density materilal are more easier to form wide band gap, and there are also more easier to form wide band gap under the same proportion. These results provide theoretical basis for the design of one-dimensional phononic crystal devices.