Organic photovoltaic cells are being considered for space applications due to the ease of fabrication, low production cost, and the potential to be used on flexible substrates. However, space-bound cells are exposed to high levels of radiation when orbiting the Earth. In this ongoing study, we examine the performance of P3HT:PCBM photovoltaic cells after exposure to gamma radiation from a cesium-137 source (662 keV). Preliminary results show degradation of the device I-V characteristics with radiation doses up to 5 krad. The integral mode time of flight (I-TOF) technique and current extraction by a linearly increasing voltage (CELIV) technique will be used to study the electron mobility and carrier lifetime properties as a function of the radiation dose. We speculate that main chain scission and reduced .-conjugation of P3HT are the dominant mechanisms responsible for performance degradation.