Unraveling the Relationship Between the UV Photostability of Conjugated Polymers and Their Molecular Structures: Triplet States Matter!

Abstract While organic solar cells have surpassed 20% efficiency, achieving long operational lifetimes remains a key challenge for their practical adoption. Developing intrinsically stable organic absorber materials capable of withstanding prolonged exposure to light for 20–30 years represents a key task, which is challenged by the limited understanding of how the intrinsic photostability of organic semiconductors is linked to their molecular structure. This work fills a gap in fundamental knowledge by presenting a systematic study of >240 conjugated polymers, focusing on their intrinsic photostability. Through the analysis of experimental results, we introduced stability descriptors for a panel of common building blocks and developed an empirical model capable of quantitatively predicting the photodegradation behavior of conjugated polymers, achieving a Pearson correlation coefficient of 0.91. Theoretical calculations further rationalized these findings, revealing the critical role of triplet states formed via back electron transfer from delocalized charge‐transfer excitons in the photodegradation process. The methodology developed in this work demonstrates exceptional predictive power, offering significant opportunities for the rational design of intrinsically stable organic semiconductor materials. By bridging the gap between molecular structure and photostability, this approach paves the way for the development of next‐generation organic solar cells with both high efficiency and long‐term durability.