Photooxidation Analysis of Two Isomeric Nonfullerene Acceptors: A Systematic Study of Conformational, Morphological, and Environmental Factors

Abstract

Despite the striking progress toward improving the efficiencies of organic solar cells (OSCs) resulting from the development of nonfullerene acceptors (NFAs), there is a rising requirement of investigation of the molecular design for achieving photochemically stable NFAs. Herein, applying two isomeric NFA molecules a‐IDTBTRh and l‐IDTBTRh based on angular‐indaceno[2,1‐b:6,5‐b′]dithiophene (a‐IDT) and linear‐IDT (l‐IDT) as the central cores, the effects of molecular conformation, aggregation behavior, and environmental factors on their photooxidation degradation processes are systematically studied. It is found that tuning regioisomeric central cores on the molecular skeleton influences the backbone conformation and conjugation, resulting in the different optoelectronic properties and molecular stacking characteristics. A strong molecular aggregation dependence of the optical losses and degradation mechanics in the annealed neat films is also observed, and it is shown that l‐IDTBTRh is much more photostable than its less‐ordered core derivative, a‐IDTBTRh. Furthermore, the effects of external environmental stresses on photobleaching behaviors of the annealed thin films are studied systematically, highlighting the role of concentrated light in accelerating photooxidation of organic materials. The results not only provide a comprehensive insight into the photooxidation properties and attenuation mechanisms of organic materials, but also suggest guidelines to rationally select materials for stable OSCs.