Cost‐Effective Acetonitrile‐Based Precursor Solution Mitigates Heterogeneous Nucleation for Efficient and Stable Perovskite Solar Cells

Abstract Solution‐processing is the primary method for fabricating high‐efficiency perovskite solar cells (PSCs), where solvent choice critically influences film formation and quality. Although additives can optimize film formation dynamics by balancing nucleation and growth of perovskite, they can also induce heterogeneous nucleation due to competitive coordination and varying crystallization kinetics, leading to compositional heterogeneity and structural disorders. Herein, a perovskite precursor solution is developed using acetonitrile (ACN) as a weak coordination host solvent instead of the traditional N , N ‐dimethylformamide (DMF). The ACN‐based perovskite precursor solution reduces heterogeneous nucleation typically caused by the competitive coordination effect of DMF, and cuts costs by half compared to DMF‐based precursor solutions. This approach promotes a single crystallization pathway via a dimethyl sulfoxide‐solvated intermediate phase to α‐FAPbI 3 , which extends the anti‐solvent operation window, and enhances the crystallinity of perovskite films, and reduces defect states. The power conversion efficiencies (PCE) of 23.62% and 20.13% is achieved for the PSC and minimodule, respectively. The PSC retains over 97% of its initial efficiency after 800 h of continuous illumination under maximum power point tracking (MPPT). These findings provide valuable insights into solvent interactions in perovskite film formation and offer a cost‐effective strategy for improving the device's performance and stability.