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

Improving the photostability of the light-harvesting blend film in organic photovoltaics is crucial to achieving long-term operational lifetimes that are required for commercialization. However, understanding the degradation factors which drive instabilities is complex, with many variables such as film morphology, residual solvents, and acceptor or donor design all influencing how light and oxygen interact with the blend film. In this work, we show how blend films comprising a donor polymer (PBDB-T) and small molecule acceptor (PC₇₁BM or ITIC) processed with solvent additive (DIO) yield very different film morphologies, device performance, and photostability. We show that DIO is retained approximately 10 times more effectively in ITIC based films compared to PC₇₁BM. Unexpectedly, we see that while high volumes of DIO reduce photostability for encapsulated ITIC devices, when oxygen is introduced DIO can improve the lifetime of PBDB-T:ITIC based cells. Here, the addition of 3% DIO doubles the T₈₀ compared to ITIC based devices without DIO, suggesting that DIO-induced morphological changes interfere with or reduce photo-oxidative reactions.