3D Volatile Solid Additives: Enhancing Molecular Crystallinity and Prolonging Exciton Lifetime for Binary Organic Solar Cells Achieving an Efficiency of 19.57%

Abstract Three–dimensional volatile solid additives are a simple, effective approach for controlling the morphology of active layer in organic solar cells (OSCs), as they provide sufficient space for the thermodynamic rearrangement of active layer components. However, the application of three–dimensional volatile solid additives has been scarcely reported, and their working mechanisms remain largely unexplored. Herein, two novel three–dimensional volatile solid additives, 2–bromobiphenyl (BB) and 2,2'–dibromobiphenyl (DBB), were introduced. The results reveal that three–dimensional structure of BB and DBB can induce molecular packing and provide sufficient space for the self–reassembly of donor and acceptor materials in active layer during thermal annealing, leading to the formation of an optimized active–layer morphology featuring enhanced molecular crystallinity and favorable phase separation. As a result, OSCs based on PM6:BTP–eC9, optimized by BB or DBB, achieved power conversion efficiencies (PCEs) of 18.07% and 19.03%, respectively, which are higher than that of OSCs without any additive (17.06%). The PCE of DBB–treated OSCs was further enhanced to 19.57% when [2–(9H–carbazol–9–yl)ethyl]phosphonic acid (2PACz) was employed as the hole transport layer, representing the highest PCE reported for additive strategies within this system. Importantly, DBB exhibits good universality with successful applications in both the PM6:Y6 and D18:Y6 systems.