Brominated isomerization engineering of 1-chloronaphthalene derived solid additives enables 19.68% efficiency organic solar cells

Using halogenated additive to optimize the active layer morphology has been proven effective in boosting the power conversion efficiency (PCE) of organic solar cells (OSCs). However, the halogenated isomerism of solid additives, which finely tunes blend morphology, has been understudied, with the associated mechanisms requiring further investigation. Herein, a brominated isomerization engineering using 1-chloronaphthalene (CN)-derived solid additives (2-bromo-1-chloronaphthalene/o-BrCN, 3-bromo-1-chloronaphthalene/m-BrCN, and 4-bromo-1-chloronaphthalene/p-BrCN, respectively) is firstly developed. Among these, p-BrCN, with symmetrically halogenated positions, exhibits a small dipole moment, facilitating an extraordinary non-covalent interaction with both donor and acceptor components. Consequently, the p-BrCN-treated active layer obtains better molecular crystallinity, π-π stacking, and phase separation, helping to improve the exciton dissociation and charge transport of OSCs. Ultimately, the p-BrCN-treated OSC based on PM6:L8-BO offers a higher PCE (18.18%) compared to those treated with o-BrCN (17.89%) and m-BrCN (17.39%). Remarkably, the p-BrCN-treated OSCs based on D18:L8-BO and D18:L8-BO:BTP-eC9 further improve PCEs to 19.14% and 19.68%, placing them among the highest values for binary and ternary OSCs, respectively. This work highlights that brominated isomerization engineering in CN-derived additives is a promising strategy to optimize morphology for obtaining efficient OSCs, and elucidates the underlying mechanism.