Radiation Hardness of Organic Solar Cells

Organic photovoltaics (OPVs) have long shown promise for application as solar power generation panels for space application due to their outstanding specific power (power generated per weight), compatibility with flexible substrates, ability to integrate devices on virtually any large area and the potentially low cost of fabrication processes. And while OPVs are now demonstrating efficiencies at or even exceeding 20%, and an extrapolated intrinsic lifetime ranging from decades to centuries under AM 1.5G illumination, their ability to withstand use in harsh space environments with high energy incident radiation is yet to be clarified. In this study, we investigate the radiation hardness of organic photovoltaics. Contrary to the common belief that organic semiconductor devices are vulnerable to rapid degradation when exposed to high energy radiation, 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. This result offers a proof-of-concept demonstration that OPVs possess radiation hardness required for successful use in extended space missions.