Assessing the outdoor photochemical stability of conjugated polymers by EPR spectroscopy

Abstract

We report the first outdoor study of the intrinsic photochemical stability of a series of conjugated polymers encapsulated in an inert atmosphere and exposed to natural sunlight illumination conditions in the Negev Desert. The photoinduced aging effects resulting in the modification of the chemical structures of the materials and the appearance of persistent radical species in the samples were revealed by EPR spectroscopy. Comparing the degradation profiles normalized to the total number of absorbed photons allowed us to establish some correlations between the chemical structures of polymers (and even particular building blocks) and their photostability. Our approach may be widely used for the facile screening of many existing conjugated polymers with respect to their intrinsic photostability under outdoor solar conditions as well as for the elaboration of guidelines for designing novel promising materials for stable and efficient organic photovoltaics.