Investigation of photodegradation in polymer solar cells blended with different fullerenes derivatives

• We compared UV–vis spectra of fresh and aged P3HT, P3HT:PCBM, and P3HT:ICBA films.
• Polymer solar cells degrade at different rates depending on the fullerene acceptor.
• Fullerene electroaffinity correlates with polymer degradation in solar cells.
• The aging has larger effects on EQE spectrum for P3HT:ICBA than for P3HT:PCBM.
• Hole mobility in P3HT decreases faster in P3HT:ICBA than in P3HT:PCBM solar cells.

To fabricate long lifetime polymer solar cells, understanding the fundamental aspects controlling the performances, stability and degradation of the devices is essential. In this study, we compare the chemical and electrical degradation behaviors of polymer solar cells based on active layers of semi-crystalline p-type polymer poly(3hexylthiophene) (P3HT) and different fullerene derivatives as acceptors. Photodegradation study by UV–visible and Fourier transform infrared (FTIR) spectroscopy and photovoltaic performance study by current–voltage measurement were done to understand and compare air stability of P3HT blended with different fullerenes. The used acceptors are indene-C(60) bisadduct (ICBA) and phenyl-C61-butyric acid methyl ester (PCBM). The obtained results show that solar cells fabricated from PCBM as acceptor are more stable than those based on ICBA. Based on the spectroscopic and electrical measurement results, it is safe to conclude that PCBM contributes more to stability of P3HT than ICBA, and that the degradation behavior is compatible with recently proposed mechanisms. Chemical properties of ICBA such as the low electron affinity could be responsible for the relative low stability of the device.