Controlled‐Disorder Asymmetrical Donors Enable Efficient All‐Small‐Molecule Solar Cells with Excellent Solution‐Processability

Abstract All‐small‐molecule organic solar cells (all‐SMOSCs) are promising candidates for next‐generation photovoltaics owing to their well‐defined molecular structures and excellent batch‐to‐batch reproducibility, yet their efficiency is limited by morphology control and processability. Here, we report three asymmetric small molecule donors—MPhS‐HF, MPhS‐OP, and MPhS‐PF—engineered with distinct side‐chain functionalities to systematically investigate the interplay between molecular design, solution‐state interactions, crystallization kinetics, and blend morphology. Among them, MPhS‐OP demonstrates delayed crystallization and favorable miscibility with the non‐fullerene acceptor L8‐BO, enabling the formation of finely interpenetrating network morphologies that facilitate efficient exciton dissociation, balanced charge transport, and suppressed recombination losses. As a result, binary MPhS‐OP:L8‐BO devices achieve a record power conversion efficiency of 18.12% under conventional spin‐coating, along with exceptional processing tolerance, maintaining > 16.4% efficiency in thick‐film, high‐speed blade‐coated, green solvent‐processed, and large‐area devices. In situ spectroscopy and thermodynamic modeling reveal that the superior performance arises from the distinct film‐formation dynamics of MPhS‐OP, which delays donor precipitation relative to L8‐BO, suppressing premature phase segregation and ensuring reproducible nano‐interpenetrating morphologies across processing conditions. This work establishes asymmetric small molecule donor design as a powerful strategy to couple molecular packing control with solution processability, offering a viable route toward scalable and high‐performance all‐SMOSCs.