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

ABSTRACT 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.