Formamidinium lead triiodide (δ-FAPbI3)-based perovskite solar cells showed remarkable potential as light harvesters for thin-film photovoltaics. Herein, the mechanochemical synthesis ofδ-FAPbI3, MAPbI3, and mixed-cation FA1−xMAxPbI3with (x= 0.3, 0.5, and 0.7) perovskite materials were prepared as a novel green chemistry method for scaling up production. Crystallinity, phase identification, thermal stability, optoelectronic properties, and nanoscale composition are discussed. The results demonstrated that the prepared mixed-cation samples are enhanced in the visible absorption region and are consistent with previous works. The crystal structure ofδ-FAPbI3was altered to a cubic structure due to the change in FA-cation. Moreover, the performance of\documentclass[12pt]{minimal}
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				\begin{document}$$\delta$$\end{document}δ-FA-based perovskites was investigated using the Solar Cell Capacitance Simulator (SCAPS-1D) software. The validity of the device simulation was confirmed by comparing it to real-world devices. The photovoltaic characteristics and impact of absorber thickness on device performance were explained. The\documentclass[12pt]{minimal}
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				\begin{document}$$\delta$$\end{document}δ-FA-based solar cell with a 50% MA-doped molar ratio shows a better performance with an efficiency of 26.22% compared to 8.43% forδ-FAPbI3. The outcome results of this work confirm the beneficial effect of mixed cations on device operation and advance our knowledge of the numerical optimization of perovskite-based solar cells.