Photostability of Conjugated Polymers—A Survey of Factors Impacting the Rates of Photodegradation

Photodegradation of conjugated polymers is one of the largest hurdles to successful implementation of these materials in a wide array of organic electronic applications, yet it remains a relatively unexplored area of research. While many of the studies that have been conducted focus on the effects of oxygen on degradation, we observe photodegradation occurring even under nearly oxygen-free conditions, suggesting fundamental degradation pathways exist. We have investigated structure property relationships, in particular how side chain branching enhances photodegradation across a family of dioxythiophene polymers. We found that linear side chains offered the best photostability, while branched side chains - especially those where branching points were near the conjugated backbones - offerred the poorest photostability. Crosslinking appeared to be the dominant form of degradation in the absence of oxygen, as opposed to more catastrophic side reactions occurring in the presence of oxygen. More recently we have explored strategies commonly used to stabilize commodity polymers - such as the use of additives or UV-blocking layers - all of which either have no impact or actually accelerate the rate of photodegradation in dioxythiophene polymers. These results provide a clearer picture of the intrinsic photodegradation of conjugated polymers, which will assist us in designing future approaches to mitigating this process.