The maximum theoretical solar conversion efficiency is calculated for an organic photovoltaic energy conversion system based on PVK‐TNF. Charge separation is assumed to take place at a Schottky barrier. At high fields (108V m−1) the theoretical energy conversion efficiency approaches a maximum value of 2% with a 2‐eV barrier. Lower efficiencies are found for barriers greater than or lower than 2.0 eV and at lower fields.