The role of additives in the film formation kinetics of active layers in organic solar cells: From in situ characterization to mechanistic elucidation

Understanding thin‐film formation kinetics is pivotal for optimizing the performance of organic solar cells (OSCs). This review provides a comprehensive overview of recent advances in employing additives to modulate the active‐layer kinetics. In situ characterization techniques have been utilized to real‐time monitor the dynamic transformation from solution to solid‐state thin films. The regulatory roles of both liquid and solid additives are discussed in key film formation stages including solvent evaporation, pre‐aggregation, phase separation and crystallization highlighting how additives tailor nanostructure evolution by tuning solvent evaporation rates, intermolecular interactions and crystallization kinetics. Finally, the review outlines current challenges and future opportunities of in situ characterization, emphasizing its potential to elucidate the correlation between dynamic film formation and morphological evolution, thereby offering valuable insights for enhancing the efficiency and stability of OSCs.