 Abstract, in order to improve the stability of polymer solar cells, we have developed two new types of small molecule acceptors which are tethered to the polymer donor by a thiophene core isomorphism engineering. The resulting dimers show increased thermal stability compared to their individual small molecule acceptor segments and isomeric counterparts. Furthermore, these dimers also exhibit enhanced device performance and long-term stability. This work demonstrates that tethered small molecule acceptors can be used to increase the stability of polymer solar cells while maintaining high device performance. This article was authored by Yang Bai, Zee Jong, Cho Choo Choo, and others.