Dual‐Additive‐Driven Morphology Optimization for Solvent‐Annealing‐Free All‐Small‐Molecule Organic Solar Cells

Abstract All‐small‐molecule organic solar cells (ASM‐OSCs), which consist of small‐molecule donors and acceptors, have recently been studied extensively to eliminate the batch‐to‐batch variation from polymer‐based donor or acceptor. On the other hand, the control of their active layer morphology is more challenging due to the similar chemical structure and miscibility of small‐molecule donor and small‐molecule accepter. Hence, this study develops a dual‐additive‐driven morphology optimization method for ASM‐OSCs based on BTR‐Cl:Y6. One solid additive – 1,4‐diiodobenzene (DIB) and one liquid additive – diiodomethane (DIM) are selected, making use of their distinct interaction mechanisms with Y6 and BTR‐Cl. It is found that DIB can form a eutectic phase with Y6, which can increase the intermolecular interactions and modulate the acceptor phase separation, while the simultaneous volatilization of DIM suppresses the over‐aggregation of BTR‐Cl during the film casting process. As a result of the synergistic morphology tuning, the optimized device delivers a power conversion efficiency (PCE) as high as 15.2%, among the highest PCE reported to date for binary ASM‐OSCs without solvent annealing treatment. This work demonstrates the potential of morphology tuning via the incorporation of dual additives into ASM‐OSCs, enabling them to achieve comparable efficiencies to those of conventional polymer/small‐molecule based OSCs.