Design of light-trapping microscale-textured surfaces for efficient organic solar cells.

Organic photovoltaic (OPV) cells suffer from low charge carrier mobilities of polymers, which renders it important to achieve complete optical absorption in active layers thinner than optical absorption length. Active layers conformally deposited on light-trapping, microscale textured, grating-type surfaces is one possible approach to achieve this objective. In this report, we analyze the design of such grating-type OPV cells using finite element method simulations. The energy dissipation of electromagnetic field in the active layer is studied as a function of active layer thickness, and pitch and height of the underlying textures. The superiority of textured geometry in terms of light trapping is clearly demonstrated by the simulation results. We observe 40% increase in photonic absorption in 150 nm thick active layer, for textures with 2 microm pitch and 1.5 microm height.