Enhanced absorptance of the assembly structure incorporating germanium nanorods and two-dimensional silicon gratings for photovoltaics.

This paper proposes an assembly structure incorporating two-dimensional silicon gratings and germanium nanorods applied to photovoltaic absorbers. The absorptance of the assembly structure is numerically investigated using the finite-difference time-domain method. The results demonstrate that such a structure can greatly improve the absorptance and conversion efficiency compared to the gratings or nanowires in the 300-1100 nm wavelength region. The average spectral absorptance of such a structure reaches up to 0.983, even closes in to unity in some wave regions, which is mainly attributed to the guided mode resonance and Fabry-Perot resonance identified by analyzing the electromagnetic field and power dissipation. The effects of different diameters and lengths of the nanorod component, as well as the widths and depths of the grating component, on the absorptance are further examined. It is found that the absorptance of the assembly structure is insensitive to the incident angle of less than 30° for both TM and TE waves. The photovoltaic absorbers with such a structure can yield an ideal conversion efficiency as high as 47.9%, which shows great potential for applying the assembly structure to photovoltaic absorbers.