Effect of temperature on the morphological and photovoltaic stability of bulk heterojunction polymer: fullerene solar cells

In high performance polymer:fullerene bulk heterojunction solar cells the nanoscale morphology of interpenetrating acceptor:donor materials is optimized through appropriate preparation conditions such as annealing and choice of solvent, but this initial state-of-the-art morphology will not remain stable during long-term operation. We report the effects of prolonged storage at elevated temperatures on both the morphology and the photovoltaic performance for the model systems mdmo-ppv:pcbm and p3ht:pcbm as compared to ‘high tg ppv’:pcbm based solar cells, where the ‘high tg ppv’ is characterized by its high glass transition temperature (138 °c). In situ monitoring of the photocurrent–voltage characteristics at elevated temperatures, in combination with a systematic transmission electron microscopy (tem) study and complementary optical spectroscopy, reveals distinct degradation kinetics and morphological changes that indicate the occurrence of different underlying physico-chemical mechanisms