Enhanced Broadband Light Trapping in c-Si Solar Cells Using Nanosphere-Embedded Metallic Grating Structure

A hexagonal nanosphere (NS)-embedded back plasmonic grating structure is proposed to improve the light absorption of crystalline silicon (c-Si) solar cells. These structures are simple, can be deposited toward the final stages of device processing, and involve no increase in the surface area of the semiconductor layer. Experimental fabrication of this structure on a 200-mu m c-Si wafer has been realized using silver, resulting in broadband absorption enhancement in the near-infrared region. In corresponding to the optical measurement, a maximum potential photocurrent density enhancement of around 2.23 mA/cm(2) has been predicted, compared with the reference with a planar metal reflector. Three-dimensional finite-element method numerical simulations were also performed on smooth and irregular surface geometries of the NSs. Our results demonstrate that while both configurations perform better than a planar reflector, the irregular nanofeatures on the gratings can adjust the optical resonance to ensure that the light is more efficiently scattered into the Si, which would significantly improve its optical absorption. These structures have the potential to be used as rear metal contacts, in addition to performing the function of a light-trapping layer without increasing the fraction of the metal component.