Non-Fused Core Linked Star-Shaped Oligomer Acceptors for over 19% Efficiency and Stable Binary Organic Solar Cells

Star-shaped oligomer acceptor represents a promising candidate to high-performance and robust organic solar cells (OSCs). However, the limited diversity of this community acceptors leaves a significant knowledge gap regarding their structure-performance relationship. Herein, we designed two new star-shaped oligomer acceptors namely 3BY and 3QY by introducing non-fused central units to bridge the Y-acceptor arms. The structural variability of non-fused cores provides an available platform to finely regulate the aggregation properties of oligomers. In particular, the triazine center of 3QY allows multisite intramolecular non-covalent interactions, which not only improve molecular self-assembly, but also refine the pre-aggregation of polymer donor and film-forming kinetics of heterojunction blend. Finally, the PM6:3QY solar cells realize a very impressive efficiency up to 19.27%, far outperforming that of PM6:3BY (17.75%) and ranking the highest efficiency among OSCs based on oligomer acceptors. Meanwhile, the considerable molecular sizes of star-shaped molecules retard molecular diffusion, affording notable device stability with a large T80% over 3000 hr for PM6:3QY device under thermal stress. This study establishes a reliable structure-performance relationship and demonstrates the great potential of non-fused core bridged star-shaped oligomers on fabrication of high-efficiency and long-term stable OSCs.