Revealing effects of phenolic solid additives on morphology and device physics for organic solar cells

Solid additives represent a potent morphological control strategy for enhancing the performance of organic photovoltaic (OPV) devices by enabling precise tuning of active layer aggregation, molecular stacking, and phase separation. These structural changes are vital for improving exciton dissociation, charge transport, and charge collection efficiency. We systematically explore the use of phenolic small molecules as solid additives, focusing on their ability to interact via hydroxyl groups with the acceptor material, potentially inhibiting excessive aggregation. Employing the PM6:Y7 system, we show that the phenolic solid additive BINOL significantly improves photovoltaic performance over both control and chloronaphthalene (CN)-processed devices. The BINOL-modified device yielded a high power conversion efficiency (PCE) of 17.60 % (vs 15.57 % for control and 16.80 % for CN). Comprehensive physical studies reveal that BINOL enhances exciton dissociation and charge transport while effectively suppressing charge recombination and reducing voltage loss. Importantly, improved device stability was also achieved. Our results underscore the promise of phenolic solid additives for realizing highly efficient and stable OPVs by beneficially regulating active layer morphology and charge dynamics.