Optimized Rear-Electrode Grating Structures in Organic Solar Cells

Design parameters for gratings at the rear electrode in organic solar cells were investigated using finite difference time domain (FDTD) simulations. By incorporating the full device layer structure, we find that the total optical absorption in the active region of the cell is influenced by the interplay between the localized surface plasmon modes at the grating and the Fabry-Perot modes of the multilayer structure and by total internal reflection of diffracted light at the ITO/glass interface. Absorption enhancements of up to 30% compared with planar structures are found with comparable enhancements for silver and for aluminium electrodes. The tolerance of the enhancements to grating geometry and to polymer layer thickness was found to be high, with implications for the fabrication of practical devices.