Bulk Synthesis of Phase‐Pure Ruddlesden‐Popper Phase Perovskites via Iodide‐Mediated Mechanochemistry

Ruddlesden‐Popper (RP) perovskites offer exceptional optoelectronic properties but face persistent challenges in achieving simultaneous control over phase purity, processability, and scalable synthesis. Here, we overcome this limitation through iodide‐mediated liquid‐assisted grinding (LAG), enabling gram‐scale synthesis of phase‐pure quantum‐well perovskites (n = 1–4) with >98% phase fidelity. By introducing hydroiodic acid (HI) during mechanochemical milling, we achieve kinetic acceleration via liquid‐phase ionic incorporation, bypassing solid‐state diffusion barriers to drive stoichiometry‐directed assembly into monophase crystals (0.1–5 µm). The resulting powders resolve scalability‐processability constraints by enabling spark plasma sintering consolidation into centimeter‐scale bulk monoliths with improved crystallographic orientation, and facilitating conformal coatings on flexible/curved substrates via screen printing. Critically, these processable forms support heterogeneous integration with 3D perovskites to create functional heterostructures. This work establishes a platform for deterministic quantum‐well design, unlocking scalable production and integration of 2D perovskites for advanced optoelectronics.