In this paper, we report an investigation of the optical and electrical properties of an organic solar cell (OSC) with a back contact grating architecture through 3-D numerical simulations. By using finite-element methods for both optical and transport properties, we have modeled the behavior of OSC with a grating architecture and compared with a conventional planar structure. Based on these optoelectrical simulations, we optimized the back contact grating, obtaining an increment of up to 17.5