The morphology of the active layer plays a crucial role in the performance of organic photovoltaics. Although volatile additives are commonly used to manipulate the morphology, their mechanism of action remain poorly understood. In this study, we conducted a systematic exploration of the mechanism of the traditional volatile additive 1-CN in film formation kinetics of typical PM6:Y6 system. We found that 1-CN induces a secondary aggregation effect, improving film morphology and promoting face-on crystalline orientation. Through elucidating its impact on exciton dynamics, we established a link between morphology optimization and increased exciton diffusion length and accelerated charge separation. Our findings unveil the unique mechanism of action of volatile additive, providing a new perspective for improving the morphology and enhancing the performance of organic photovoltaic devices.