AbstractA pyrene‐fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive “butterfly‐like” structure, comprising two Y‐acceptors as wings fused with a pyrene‐based backbone. The extended π‐conjugated backbone and the electron‐donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (T_g), and low‐lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non‐radiative voltage loss, and elevating open‐circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high T_g exhibited by the pyrene‐fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal‐treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the “butterfly‐like” design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs.