Diffusion‐Limited Accepter Alloy Enables Highly Efficient and Stable Organic Solar Cells

Abstract Organic solar cells (OSCs) are designed based on a blend of polymer donor and small molecular acceptor whereby the thermodynamic relaxation of the morphology raises the concerns related to operational stability. Herein, it is demonstrated that the classical Y6‐based binary device can be stabilized by using its derivative of ZCCF3 as the third component, which is designed with the replacing of the thiadiazole group on Y6 with the trifluoromethyl substituted diazepine unit. ZCCF3 delivers not only higher glass transition temperature ( T g ) than Y6 but also have hyper‐miscibility with Y6, contributing to a favorable diffusion‐limited Y6:ZCCF3 alloy when blended with polymer donor. Consequently, a champion power conversion efficiency of 18.54% is achieved in the optimal PM6: Y6: ZCCF3 devices, which can retain their 80% initial efficiency of up to 360 h. This study highlights the importance of high T g of the third component and its derived hyper‐miscible accepter alloys in achieving highly efficient and stable OSCs.