Atomic Optimization on Pyran‐Fused Nonfullerene Acceptor Enables Organic Solar Cells with an Efficiency Approaching 16% and Reduced Energy Loss

Atomic replacement on platforms of nonfullerene acceptor (NFA) with already excellent performance is expected to further optimize the energy levels, absorptions, and even charge transfer dynamics of NFAs effectively without greatly destroying their superior molecular conformations. On the basis of high‐performance F‐series NFAs, the structural optimization at atomic level is performed by replacing sulfur atoms in FO‐2Cl with selenium atoms, thus affording a new NFA labeled as FOSe‐2Cl. FOSe‐2Cl not only inherits the good planar configuration of FO‐2Cl, but also exhibits more suitable energy levels, redshifted absorption, enhanced molecular packing, and accelerative charge transfer/transport dynamics compared with those of FO‐2Cl. With a widely used polymer PM6 as the donor, organic solar cell (OSC) based on FOSe‐2Cl affords a significantly improved power conversion efficiency (PCE) of 15.94% with a reduced energy loss (Eloss) of 0.670 eV, with respect to that of FO‐2Cl‐based OSC with a PCE of 14.94% and Eloss of 0.706 eV. The result represents the best performance reported to date for pyran‐fused NFAs and F‐series NFAs‐based binary OSCs, providing another promising platform to achieve the state‐of‐the‐art OSCs in addition to the well‐known Y‐series NFAs.