Macrocyclic Encapsulation-Driven Asymmetric Terthiophene Acceptors with Hierarchical Stacking and High “Unit Economy” for Efficient Organic Solar Cells

Nonfused ring electron acceptors (NFREAs) have emerged as promising candidates for high-efficiency organic solar cells, owing to their cost-effectiveness. Notably, the number of aromatic rings in their nonfused conjugated backbones plays a crucial role in determining optical and electronic properties, as well as molecular packing and orientation. Herein, a simple terthiophene backbone was employed to construct the asymmetric acceptor R3T-4F via a macrocyclic encapsulation strategy, while I3T-4F with the traditional sterically hindered substituents was designed as a control molecule. With the symmetry breaking, both acceptors exhibited multiple π–π stacking modes with hierarchical characteristics, whereas an even more compact packing was achieved by R3T-4F, significantly facilitating intermolecular charge transport and resulting in a pronounced bathochromic shift in the absorption spectrum. Furthermore, the R3T-4F blend film exhibits a well-defined nanofiber network morphology, effectively suppressing charge recombination and enhancing the charge transport. As a result, devices based on R3T-4F achieved the highest power conversion efficiency (PCE) of 15.04% among the terthiophene-based acceptors and exhibited excellent “unit economy” for the individual contribution of each thiophene unit to photovoltaic performances.