High‐Performance Ternary Organic Solar Cells via Isomeric Engineering of Nonfullerene Guest Acceptors

Constructing ternary blends has been considered as a feasible approach to achieve highly efficient organic solar cells; however, the delicate choice of the guest components still needs labor-intensive and time-consuming work. Herein, the isomeric effects of guest nonfullerene acceptor on the physicochemical and photovoltaic properties of ternary OSCs are systematically investigated. Two isomeric NFAs, BTP-γ-Br and BTP-δ-Br, with different bromine-substituted sites on IC terminal groups were designed and synthesized. BTP-δ-Br exhibits a larger dipole moment with red-shifted absorption and tends to form overagglomerations with strong self-aggregation behavior, while BTP-γ-Br shows weaker crystallinity with face-on molecular orientation. The single crystal of BTP-γ-Br revealed that a special C≡N…H noncovalent interaction between the adjacent molecules can enhance intermolecular interactions. The D18:BTP-γ-Br-based binary OSCs delivered a reduced nonradiative energy loss (0.18 eV) and a high V_OC of 0.931 V. Moreover, with the addition of isomeric NFAs into the D18:N3 host system, the D18:BTP-γ-Br:N3-based ternary blends exhibited improved crystallinity with clear fibril networks, thus enhancing the efficient exciton dissociation and charge transport. Consequently, a high PCE of 19.2% (certified 18.9%) was obtained for D18:BTP-γ-Br:N3-based devices. These results imply that rational design of guest NFAs is an efficient route to construct high-performance OSCs.