The burgeoning power conversion efficiency (PCE) of the organic halide-based perovskite (OHP) solar cells (PSCs) in recent decades has been regarded as a promising candidate for next-generation photovoltaic (PV) application. However, the presence of organic cations in OHP structures causes environmental stability issues. The importance of a total inorganic device, such as a Cs⁺-based perovskite structure, is its ability to exhibit a high PCE. However, the main issue of Cs-based perovskites is its high processing temperature, which limits the fabrication of flexible PSC devices. The current work on a solvent-free mechanochemical pre-synthesis approach for CsPbIBr₂ is demonstrated to produce a highly crystalline structure at a lower temperature (110 °C) than previously reported in the literature. In addition, additive incorporation, such as methylammonium chloride (MACl) to CsPbIBr₂, successfully modulates the in-built lattice strain from compressive to tensile, which enhances the overall device performance. In particular, 10 mg mL⁻¹ MACl incorporation within CsPbIBr₂ (CsPbIBr₂-10MACl) shows a PCE of 8.25%, which is 57.44% higher than that for pristine CsPbIBr₂ (5.24%)-based cells utilizing an inverted planar device architecture constituting FTO/CuI/CsPbIBr₂-xMACl/Al. Interestingly, the pre-synthesized perovskite powder to obtain a thin film-based device fabrication process outruns the existing CsPbIBr₂-PSC technology in terms of efficiency and long-term stability.