Effective medium analysis of absorption enhancement in short-pitch metal grating incorporated organic solar cells.

The effective medium theory is applied to analyze the absorption enhancement in organic solar cells with a short-pitch metal grating. A 37% improvement in the absorption of the active layer is achieved with respect to that of a planar control cell. It is inspired that the propagating surface plasmon modes are excited at the interface between the effective medium layer and the flat metal plate, resulting in a reduction of light reflection. In real structure, the electric field redistributes with its intensity in the region with active materials infiltrated in the grooves increases significantly, exhibiting like hot spots to assist in achieving broadband absorption enhancement. Moreover, the localized surface plasmon resonances excited at the top of the metal ridges also contribute to the absorption enhancement in the cells.