Perovskite quantum dots (PQDs) are highly promising for next-generation photovoltaics due to room-temperature solution-processability and excellent optoelectronic properties. Size-tunable bandgap makes monodispersity essential to prevent bandtail broadening. However, high reactivity and low formation energy cause polydispersity during gram-scale synthesis, degrading device performance. Here, we present ligand-coordination-driven precursor diffusion control that decouples monomer formation from nucleation/growth, enabling gram-scale synthesis of monodisperse CsPbI₃ PQDs. Furthermore, FA⁺ diffusion regulation via acid-base equilibrium yields well-alloyed CsₓFA₁₋ₓPbI₃ PQDs with high monodispersity. These PQDs achieve 16.7% power conversion efficiency, retaining >15% efficiency under gram-scale conditions with enhanced device stability, establishing a scalable platform for commercial PQD photovoltaics.