Impressive Radiation Stability of Organic Solar Cells Based on Fullerene Derivatives and Carbazole-Containing Conjugated Polymers

We explored the radiation stability of carbazole-based electron-donor conjugated polymers, acceptor fullerene derivative [60]PCBM, and their blends as active layer components of organic solar cells. An exposure to γ rays induced evident degradation effects in bulk samples of the pristine fullerene acceptor ([60]PCBM) and two investigated electron-donor conjugated polymers: PCDTBT and PCDTTBTBTT. The most severe radiation damage occurred in [60]PCBM as can be concluded from the significant losses in open circuit voltage, fill factor, and efficiency of photovoltaic (PV) devices comprising the exposed fullerene acceptor. Conjugated polymers PCDTBT and PCDTTBTBTT showed substantially different radiation stabilities: the samples of PCDTTBTBTT exposed to 200 Gy lost ∼25% of their nominal photovoltaic efficiency due to a substantial decay of all device parameters, while PCDTBT alone showed just a minor aging under the same conditions. The fullerene-polymer composites were much more resistant with respect to the radiation damage than the bulk samples of pristine materials. In particular, the PCDTBT/[60]PCBM composite films demonstrated an outstanding radiation stability while maintaining more than 80% of the initial photovoltaic efficiency after exposure to γ rays with a maximum absorbed dose of 6500 Gy. Considering an average annual radiation dose of 160 Gy according to the NASA estimations for satellites at geocentric Earth orbits, organic solar cells based on PCDTBT/[60]PCBM blends hold a promise to deliver lifetimes well above 10 years. The revealed impressive radiation stability of PCDTBT/[60]PCBM blends in combination with other advantages of organic solar cells, for example, their mechanical flexibility and lightweight, points to a bright future of this PV technology in space industry applications.