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We report the synthesis of organometal halide perovskites by milling CH₃NH₃I and PbI₂ directly with an Al₂O₃ scaffold to create hybrid Al₂O₃-CH₃NH₃PbI₃ perovskites, without the use of organic capping ligands that otherwise limit the growth of the material in the three dimensions. Not only does this improve the ambient stability of perovskites in air (100 min versus 5 min for dimethylformamide (DMF)-processed material), the method also uses much fewer toxic solvents (terpineol versus dimethylformamide). This has been achieved by solid-state reaction of the perovskite precursors to produce larger perovskite nanoparticles. The resulting hybrid perovskite−alumina particles effectively improve the hydrophobicity of the perovskite phase whilst the increased thermal mass of the Al₂O₃ increases the thermal stability of the organic cation. Raman data show the incorporation of Al₂O₃ shifts the perovskite spectrum, suggesting the formation of a hybrid 3D mesoporous stack. Laser-induced current mapping (LBIC) and superoxide generation measurements, coupled to thermogravimetric analysis, show that these hybrid perovskites demonstrate slightly improved oxygen and thermal stability, whilst ultra-fast X-ray diffraction studies using synchrotron radiation show substantial (20×) increase in humidity stability. Overall, these data show considerably improved ambient stability of the hybrid perovskites compared to the solution-processed material.