Green pathway to 14.51% efficiency in all-small-molecule organic solar cells: apigenin-mediated morphology control with halogen-free processing

All-small-molecule organic solar cells (ASM OSCs) have emerged as promising photovoltaic technologies due to their excellent batch-to-batch reproducibility and potential for scalable manufacturing. However, the development of eco-friendly processing protocols using halogen-free solvents combined with sustainable solid additives remains unexplored, despite being crucial for realizing green and efficient ASM OSC production. Herein, we demonstrate the first successful integration of plant-extracted apigenin (AP) as a green solid additive with tetrahydrofuran (THF), a non-halogenated processing solvent, in ASM OSC fabrication. Systematic investigations reveal that AP establishes hydrogen-bonding interactions with the acceptor molecules, thereby promoting tighter molecular packing and enhancing crystallinity. Simultaneously, the additive modulates donor–acceptor miscibility to optimize phase-separated domain sizes. These synergistic effects generate a well-interconnected nanomorphology with balanced charge transport pathways, effectively facilitating exciton dissociation while suppressing charge recombination. The resultant devices obtain a remarkable power conversion efficiency (PCE) of 14.51%, representing one of the highest performances among halogen-free processed binary ASM OSCs reported to date. This pioneering work establishes a viable pathway toward sustainable OSC manufacturing by demonstrating that eco-friendly additives can synergistically cooperate with non-halogenated solvents to simultaneously enhance device performance and process sustainability.