| Summary: | Organic solar cells working under continuous light irradiation are prone to photo-induced degradation. Photostabilities of benzodithiophene- alt -2-decyltetradecyl substituted isoindigo (PBDTI-DT) copolymer in solution, and as pristine film, and a PBDTI-DT:PC _60 BM bulk hetero-junction (BHJ) film were investigated for more than 70 h under simulated AM 1.5 solar irradiation. The photodegradation kinetics studied in standalone polymer chains were found to be fast due to the absence of intermolecular interaction while the inter-chain interaction in the polymer films kept the backbone intact against light-induced degradation. Further addition of PC _60 BM in the polymer made the BHJ film more stable as PC _60 BM serves as photoprotective layer and radical scavenger. This conclusion was supported by the similar XRD traces of PBDTI-DT:PC _60 BM film during degradation while the traces of the pristine film indicated bleaching and shifted with increasing photon stress. In addition, the absorption of PBDTI-DT:PC _60 BM and pristine PBDTI-DT films were reduced to 80 and 56%, respectively, after 70 h of photo-degradation.
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