High-Performance Nonfused Ring Electron Acceptors with Well-Controlled Branching Position of the Alkoxy Side Chain

Side-chain engineering has a profound impact on regulating the properties of the acceptors such as aggregation behavior, solubilities, charge transport, blend film morphology, etc. In this work, we designed and synthesized three nonfused ring electron acceptors (NFREAs), XY-OC24, XY-OC6, and XY-OC2C4, through precise adjustment of the alkyl chain's branching degree and position. These acceptors carry a diphenylamine unit at one side and hexyl-, 2-ethylhexyl, and 3-heptyl-based alkoxy side chains at the opposite side of the molecular backbone. Consequently, due to the greater steric hindrance afforded by alkoxy side chains, XY-OC24 demonstrates enhanced solubility, and the corresponding blend film displays reduced domain sizes, a bicontinuous fibrous interpenetrating network, and predominant face-on orientation. These characteristics collectively facilitate charge transport, suppress recombination, and improve charge extraction, enabling XY-OC24 organic solar cells (OSCs) to achieve a high power conversion efficiency of 16.29%. This study provides critical insights into NFREA design, elucidating the working mechanisms through which side-chain engineering optimizes the morphology and device performance, thereby advancing the OSC technology.