Strategic Inner/Outer Side-Chain Tuning for High-Efficiency Green-Solvent-Processed Organic Solar Cells

• • PM6:BTP-TO12 binary blend achieves a PCE of 18.2% under green-solvent (toluene) processing, demonstrating that balanced solubility and molecular packing order are critical for high efficiency. • • Ternary OSCs incorporating BTP-TO12 as a guest material reach a PCE of 19.5%, representing state-of-the-art performance for halogen-free solvent-processed devices and highlighting the potential for industrial scalability. • • Systematic variation of inner and outer side-chain lengths reveals that longer alkyl chains do not always improve performance; excessive solubility reduces molecular packing order, leading to lower fill factor and efficiency. • • BTP-TO12 exhibits low energy loss and well-controlled aggregation in toluene, which are key factors in achieving high open-circuit voltage and fill factor, as evidenced by the 19.5% PCE in ternary devices.