Radiation hardness of organic photovoltaics

Abstract

We investigate the resilience of organic photovoltaic (OPV) cells to proton irradiation at doses equivalent to that experienced by spacecraft in low earth orbit. The OPVs, with their inherent flexibility, light weight, low temperature processing, and potential to achieve high specific power of 40 W/g, are promising candidates for energy production in space. However, their ability to withstand irradiation by high-energy incident radiation and subatomic particles characteristic of harsh space environments is yet unproven. We find that small-molecule OPVs grown by vacuum thermal evaporation are resistant to degradation by 30 keV proton irradiation, in contrast to polymer-based OPVs that suffer a 50% efficiency loss under similar conditions. Thermal annealing at low temperatures significantly restores the polymer-based OPV power conversion efficiency. The loss of efficiency is attributed to cleavage of pendant alkyl groups on the polymers, resulting in cross-linking and the subsequent formation of deep electronic traps.