Exploring\nthe Impact of 1,8-Diioodoctane on the Photostability\nof Organic Photovoltaics

Improving the photostability\nof the light-harvesting blend film\nin organic photovoltaics is crucial to achieving long-term operational\nlifetimes that are required for commercialization. However, understanding\nthe degradation factors which drive instabilities is complex, with\nmany variables such as film morphology, residual solvents, and acceptor\nor donor design all influencing how light and oxygen interact with\nthe blend film. In this work, we show how blend films comprising a\ndonor polymer (PBDB-T) and small molecule acceptor (PC<sub>71</sub>BM or ITIC) processed with solvent additive (DIO) yield very different\nfilm morphologies, device performance, and photostability. We show\nthat DIO is retained approximately 10 times more effectively in ITIC\nbased films compared to PC<sub>71</sub>BM. Unexpectedly, we see that\nwhile high volumes of DIO reduce photostability for encapsulated ITIC\ndevices, when oxygen is introduced DIO can improve the lifetime of\nPBDB-T:ITIC based cells. Here, the addition of 3% DIO doubles the <i>T</i><sub>80</sub> compared to ITIC based devices without DIO,\nsuggesting that DIO-induced morphological changes interfere with or\nreduce photo-oxidative reactions.