Energetic Disorder in A‐D‐A Type Acceptors for Organic Photovoltaics: Fused‐Ring vs. Nonfused‐Ring Systems

Abstract

ABSTRACT Reducing the energetic disorder is crucial to improve the efficiencies of organic photovoltaics. Given the high performance of both fused‐ring and nonfused‐ring A‐D‐A type acceptors, a fundamental question arises: is a fused‐ring D‐unit necessary to obtain low energetic disorder? Here, we have systematically investigated the energetic disorder for electrons (described by the standard deviation of the lowest unoccupied molecular orbital (LUMO) energy, σ LUMO ) in representative fused‐ring and nonfused‐ring A‐D‐A type acceptors by combining molecular dynamics simulations with density functional theory calculations. The results point out that the σ LUMO is dominated by the dynamic disorder for both fused‐ring and nonfused‐ring systems. Moreover, for all these acceptors, the LUMO is delocalized over the entire molecular backbone, which benefits to reduce the electron‐vibration coupling. Consequently, both fused‐ring and nonfused‐ring systems exhibit low σ LUMO values of 48–56 and 50–71 meV, respectively. Compared to the fused‐ring systems with similar conjugation lengths, the σ LUMO is slightly increased for the nonfused‐ring systems due to the extra rotation‐induced static disorder. Notably, the σ LUMO of the nonfused‐ring systems can be effectively reduced by extending the D‐units and restricting the conformational rotation. This work provides helpful insights for developing cost‐effective nonfused‐ring acceptors with low energetic disorder.