Cold‐Sublimating Quasi‐Solid Additive Enables High Efficiency and Long Operational Stability Binary Organic Solar Cells

ABSTRACT Controlling activelayer morphology during drying is pivotal for the simultaneous realization of high efficiency and durability in Yseries organic solar cells (OSCs). Here, we uncover how the physical state of in situ removable (ISR) isomeric additives, o DF (liquid), m DF (quasisolid), and p DF (solid), governs film formation, molecular ordering, and device stability in binary OSCs. Among them, quasisolid m DF functions as a coldsublimating transient structuring agent: it widens earlystage solvent removal window yet accelerates intermediate crystallization, tightens π–π stacking, enlarges coherence length, and programs a favorable vertical phase separation, as resolved by in situ UV–vis, GIWAXS, and depthprofiled spectroscopy. m DF interacts most strongly with L8‐BO while fully evaporating from the film, minimizing nonradiative losses and avoiding the adverse impact of residual additives on device stability. Consequently, PM6:L8BO devices reach 19.28% PCE with improved carrier mobility and suppressed trapassisted recombination; applying m DF to D18:L8BO yields 20.08%. Under 1sun illumination at 70 °C, m DF extends operational stability to T 80 = 477 h, outperforming o DF (58 h), p DF (279 h), and additivefree control (103 h). These results establish physicalstateprogrammed ISR additives as a general route to cooptimize efficiency and stability in OSCs and provide mechanistic guidance for scalable, residuefree morphology control.