Transient photovoltage and charge extraction analyses are employed to analyze charge carrier densities and bimolecular recombination dynamics in organic polymer: fullerene solar cells under open circuit operating conditions, employing four different donor polymers. An equation that allows us to calculate the device V-OC from these kinetic measurements is derived. This equation allows us to calculate the voltage output of devices within +/- 25 meV of directly measured values. This analysis thus allows us to relate the device open circuit voltage directly to the kinetics of bimolecular recombination, and thereby the influence of nanomorphology upon device voltage output.