A fourteen peripherally fluorinated dimeric acceptor enables organic solar cells achieve 19.7 % efficiency

The oligomeric small-molecule acceptors (OSMAs) could combine the advantages of small-molecule acceptors (SMAs) and polymerized acceptors (PSMAs), including the definite molecular structures, high glass transition temperatures and low diffusion rates. However, a reduction in molecular symmetry and planarity usually decreases the intermolecular stacking strength and ordering, thus lowering the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Herein, the maximum fluorination was conducted on the periphery of two-dimensional plane of OSMA, rendering a 14 fluorine-containing dimeric acceptor of CH14F which affords the most fluorine-rich molecular backbone among all the OSMAs currently. The sufficient peripheral fluorination of backbone leads to more compact and orderly molecular packing and consequently improved the fill factor of OSCs. As a result, the PM6:CH14F:CH6 ternary device achieved a first-class PCE of 19.72 %. More importantly, the PM6:CH14F device retained over 80 % of initial PCE after being continuously heated at 65 °C for 1032 h. Our work demonstrates that implementing sufficient peripheral fluorination on OSMAs could conquer the molecular stacking disorder through the significantly enhanced fluorine-induced secondary interactions, thereby providing a new insight into OSCs with excellent efficiency and stability simultaneously.