We propose an elliptical silicon nanohole (SiNH) array for broadband light absorption in thin film silicon solar cells. Our analysis shows that this architecture is capable of increasing the ultimate efficiency of a thin film silicon solar cell by 17.6 % in comparison to that of the circular SiNH array with the same fill fraction. Lattice symmetry breaking and extension of the irreducible Brillouin zone are responsible for the enhancement of the absorption.
Perpendicular dual-grating (PDG) guided-mode resonance filters were constructed by placing two identical one-dimensional waveguide gratings close to and their grooves perpendicular to each other with a nano air gap between them. Multilayer waveguide theory was used to estimate the split of the resonant reflection peaks corresponding to the
TE and TM modes, and the rigorous coupled wave analysis (RCWA) was used to investigate the resonant wavelength, the linewidth of the resonant peaks, and electric field intensity distribution in the filter structures. The filters present identical spectral characteristics for normally incident wave with arbitrary polarization. The TM<sub>0</sub><sup>1</sup> and the TM<sub>0</sub><sup>1</sup> modes
are found displaying the greatest wavelength shift for the air gap variation between 0 and 100 nm, and 100 nm and 1000
nm，respectively. The coupling between the TE and TM modes is much greater in the g/w/a/w/g structure than that in the
w/g/a/g/w structure, since there is no space between the two waveguide layers in the former. The resonant peaks of the TM<sub>0</sub><sup>1</sup> mode for the one-dimensional PDG g/w/a/w/g structure exhibit narrower width compared with those for the two-dimensional g/w/a/w/g structure. In addtion, the horizontal shift between the two gratings does not influence the
measured spectra, although it will certainly have great effect on the resonant peak width if the measurement were carried
out by the guided-mode filters where the two gratings are two dimensional.