In recent years, there has been a remarkable surge in the efficiency of perovskite solar cells (PSCs), primarily attributed to advancements in device architecture optimization and thin film deposition techniques. Among various crucial factors, the electron transporting layer and the uniformity of perovskite deposition play pivotal roles in enhancing PSC performance. Notably, the incorporation of alkylammonium chloride, such as methylammonium chloride (MACl), has been instrumental in improving perovskite crystallinity and homogeneity. However, the intricate chemical interactions among formamidinium lead iodide (FAPbI₃) perovskites, MACl additives, and their byproducts have remained poorly understood. Our research focuses on elucidating these interactions, particularly concerning the formation of methyl formamidinium (MFA⁺) byproducts and their impact on PSC performance. Through systematic investigations, we uncover the prevalence of cis/trans N-methyl formamidinium iodide (MFAI) isomers and their role in promoting the growth of fully formed MFAPbI₃ 2H-phase perovskite. Furthermore, our study explores the influence of solvent choice and environmental factors on precursor solution stability and PSC reproducibility. These findings offer valuable insights into optimizing PSC fabrication processes for achieving high efficiency and long-term stability.