Guiding Morphology Evolution via Solid‐State Relaxation for Highly Reproducible and Robust Organic Photovoltaics

ABSTRACT Poor device reproducibility and insufficient processing robustness hinder organic photovoltaics (OPVs) industrialization, primarily due to poor morphological reproducibility of the active layer. Here, we establish a direct correlation between the morphology evolution pathway and morphological reproducibility. When evolution is governed by solid‐state relaxation, the active layer converges into energetically similar low‐energy metastable ensembles, yielding highly reproducible morphologies. In contrast, rapid quenching traps the active layer in a broad distribution of low‐energy metastable states, leading to poor morphological reproducibility. This principle is validated through two independent approaches: molecular structure design and additive engineering. Chemically, acceptor dimerization (PM6:DY2) shifts evolution from quenching‐ to relaxation‐dominated, reducing the coefficient of variation ( CV , a reproducibility measure) from 2.14% to 1.19% and increasing the performance figure of merit ( P‐FOM , a robustness measure) from 0.925 to 0.944. Physically, replacing the additive 1,2,4‐TCB with 1,3,5‐TIB delays the evolution of PM6:L8‐BO to the relaxation stage, achieving 19.59% PCE while achieving a record‐low CV of 0.86% (reduced from 1.55%) and increasing P‐FOM from 0.935 to 0.955. These findings establish a general principle: solid‐state relaxation‐dominated evolution leads to morphological convergence and device performance consistency, providing a theoretical basis for rational design toward high reproducibility and robustness in OPVs.