The modular structure of small molecular acceptors (SMAs) allows for versatile modifications of the materials and boosts the photovoltaic efficiencies of organic solar cells (OSCs) in recent years. As a critical component, the endcaps of SMAs have been intensively investigated and modified to control the molecular aggregation and photo-electronic conversion. However, most of the studies focus on halogenation or π-fusion extension of the endcap moieties, but overlook the non-fused π-extension approach, which could be a promising strategy to balance the self-aggregation and compatibility behaviors. Herein, we reported two new acceptors namely BTP-Th and BTP-FTh based on non-fused π-extension of the endcap by chlorinated-thiophene, of which the latter molecule has better co-planarity and crystallinity because of the intramolecular noncovalent interactions. Paired with donor PBDB-T, the optimal device of BTP-FTh reveals a greater efficiency of 14.81% that that of BTP-Th (13.91%). Nevertheless, the BTP-Th based device realizes a lower energy loss, enabling BTP-Th as a good candidate to serve as guest acceptor. As a result, the ternary solar cells of PM6:BTP-eC9:BTP-Th output a champion efficiency up to 18.71% with enhanced open-circuit voltage. This study highlights the significance of rational decoration of endcaps for the design of high-performance SMAs and photovoltaic cells.