Temporally stepwise crystallization via dual-additive orchestration: resolving the crystallinity-domain size paradox for high-efficiency organic photovoltaics

Achieving simultaneous enhancement of crystallinity and optimal domain size remains a fundamental challenge in organic photovoltaics (OPVs), where conventional crystallization strategies often trigger excessive aggregation of small-molecule acceptors. This work pioneers a kinetic paradigm for resolving the crystallinity-domain size trade-off in organic photovoltaics through dual-additive-guided stepwise crystallization. By strategically pairing 1,2-dichlorobenzene (o-DCB, low binding energy to Y6) and 1-fluoronaphthalene (FN, high binding energy), we achieve temporally decoupled crystallization control: o-DCB first mediates donor-acceptor co-crystallization during film formation, constructing a metastable network, whereupon FN induces confined Y6 crystallization within this framework during thermal annealing, refining nanostructure without over-aggregation. Morphology studies reveal that this synergy enhances crystallinity of (100) diffraction peaks by 21 %–10 % versus single-additive controls (o-DCB/FN alone), while maintaining optimal domain size. These morphological advantages yield balanced carrier transport (μ_h/μ_e = 1.23), near-unity exciton dissociation (98.53 %), and a champion power conversion efficiency (PCE) of 18.08 % for PM6:Y6, significantly surpassing single-additive devices (o-DCB: 17.20 %; FN: 17.53 %). Crucially, the dual-additive strategy demonstrates universal applicability across diverse active layer systems, achieving an outstanding PCE of 19.27 % in PM6:L8-BO-based devices, thereby establishing a general framework for morphology control in high-efficiency OPVs.