Photo-degradation in air of spin-coated PC60BM and PC70BM films

Impact of intentional photo-oxidation of a donor polymer and PC70BM on solar cell performance

“…We note that the spectra show data that have not been normalized with respect to any specific absorption band. As reported in our previous work, 26 these new features in the carbonyl region of the FT-IR spectrum are due to oxygen that has attached to carbons in the C 70 cage. This implies that new carbonyl structures are formed, most likely in different types of binding configurations.…”

“…1b, corresponds with the CQO stretch vibration of the ester group in the side chain of the molecule. 26 Upon exposure of the PC 70 BM films to light in air, this central peak remains nearly unchanged in position and intensity, but at the same time new features appear, both on the low wavenumber side and on the high wavenumber side of this central peak, that grow with increasing exposure time, as seen in Fig. 1b.…”

“…17 In contrast to the TQ1:PC 60 BM blend (Hansson et al 27 ), the presence of TQ1 decelerates the photo-oxidation of the PC 70 BM component in the TQ1:PC 70 BM blend. Given the slightly lower rate of photo-oxidation for PC 70 BM as compared to PC 60 BM, 26 this then implies that the TQ1:PC 70 BM blend must be more stable against photo-oxidation than the TQ1:PC 60 BM blend.…”

“…By a comparative FT-IR study we recently demonstrated that the rate of carbonyl growth on PC 70 BM is lower than that on PC 60 BM, when thin films are exposed to simulated sunlight and ambient air. 26 Several studies of polymer/fullerene blends have demonstrated that the presence of PC 60 BM in a blend slows down the photo-bleaching of the donor polymer, e.g., MDMO-PPV, 19 P3HT 23 and TQ1, 27 explaining this by the oxygen scavenger role of the fullerene derivative. On the other hand, the photooxidation of the PC 60 BM itself was found to be accelerated by its dispersion in a TQ1 matrix, which Hansson et al 27 assigned to the enhanced absorption range.…”

Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V

“…Similar to other OSCs based on polythiophenes and C 60 derivatives, the eco-friendly devices presented here quickly photo-degrade when operated in air. Replacing the easily photo-oxidized fullerene C 60 derivatives with the more stable fullerene C 70 derivatives or with novel water-processable non-fullerene derivatives could be the adequate strategy to increase both the efficiency and stability of water-processed OSC active layers [35,36]. However, unlike water-soluble fullerene C 60 derivatives, there has not been much research on water-soluble C 70 derivatives or water-soluble non-fullerene acceptors up to now.…”