Enhancing the Intrinsic Stability of Nonfullerene Acceptors through Dimerization via Ring‐locking Strategy^†

Comprehensive Summary The power conversion efficiencies (PCEs) of non‐fullerene acceptor (NFA)‐based organic solar cells (OSCs) have undergone an exciting development in recent years, but the poor intrinsic stability of exocyclic ethylene bridges in NFAs poses a significant challenge to their commercialization. In this work, we propose a new pyran‐locking strategy that can stabilize the exocyclic ethylene bridge connecting the strong electron‐deficient 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile end group, based on which two dimerized NFAs (ITBIC‐F and TBTBIC‐F) with an A‐D‐π‐A‐π‐D‐A structure have been successfully synthesized with significantly improved chemical and photochemical stabilities in comparison with traditional NFAs without the ring‐locked structure. The ITBIC‐F and TBTBIC‐F ‐based OSCs not only achieve promising PCEs of 13.03% and 10.01%, respectively, but also show good device stability; the ITBIC‐F‐based unencapsulated devices can retain 75% and 62% of their initial PCEs, respectively, under continuous heat (85 °C) and light irradiation (LED, 100 mW·cm –2 ) in a nitrogen atmosphere.