Polyfluorophenyl quinoxaline derived acceptors with long exciton diffusion length for efficient thin-film/thick-film organic solar cells

Designing small-molecule acceptors (SMAs) with long exciton diffusion length (L_D) and high electron mobility is vital for boosting power conversion efficiency (PCE) of organic solar cells (OSCs). However, the limited L_D of most advanced SMAs hinders their practical applications in thick-film OSCs. Herein, we develop four SMAs (named Yq-0F, Yq-2F, Yq-4F, and Yq-6F) with fluorine-free/fluorinated phenyl-substituted quinoxaline cores by manipulating the number of fluorine atom. Among them, polyfluorophenyl-substituted Yq-4F exhibits superior 3D network crystal framework and favourable intermolecular packing, leading to optimal blend morphology with polymer donor D18. Therefore, D18:Yq-4F system achieves improved carrier mobilities and suppressed charge recombination loss. Consequently, the D18:Yq-4F based binary OSCs provide a PCE of 18.30%, surpassing these ones based on D18:Yq-0F (11.27%), D18:Yq-2F (17.73%), and D18:Yq-6F (17.00%). When introducing Yq-4F as a guest into D18:L8-BO host to fabricate ternary OSCs, the PCE further increases to 20.77%, as the highest reported value among quinoxaline-derived SMAs. Moreover, ternary D18:Yq-4F:BTP-eC9 and D18:L8-BO:Yq-4F OSCs with ~500 nm active layer thickness offer impressive PCEs of >17%, ranking among the top values for thick-film devices with similar thickness. This work offers an effective SMA design strategy for opening a path towards efficient thin-film and thick-film OSCs simultaneously.