Although room temperature ionic liquids (RTILs) themselves are green solvents, their green synthesis faces great challenges actually. Mechanochemistry is developing as a new discipline with the advantages of solvent-free, green processes without high temperature and pressure. In this work, we obtained 1-methyl-3-benzyl-imidazolium iodide by directly mixing iodobenzenemethane and N-methylimidazole in a planetary ball mill using mechanochemical synthesis, and applied the product to passivate crystal defect energy levels in printable mesoscopic perovskite solar cells. Unlike ordinary thermochemical reactions, the reaction power of mechanochemistry is mechanical energy rather than thermal energy, so the reaction can be completed without high temperature, high pressure and other harsh conditions, and the whole experimental process is green and convenient. After dosage optimization, the short-circuit current density (J_SC), fill factor (FF) and photoelectric conversion efficiency (PCE) of the solar cells increase from 16.19 mA•cm^‒2, 68.04% and 10.00% to 17.59 mA•cm^‒2, 71.89% and 11.47%, respectively. Combining scanning electron microscopy (SEM) images, X-ray diffraction (XRD) tests, photoluminescence (PL) tests, time-resolved fluorescence spectroscopy (TRPL) tests, and X-ray photoelectron spectroscopy (XPS), we demonstrated that, on the one hand, the lone pair of electrons of the nitrogen atom on the imidazole ring has a dispersing effect on the charge of uncoordinated Pb²⁺ on the surface of the perovskite crystal, and on the other hand, the electrostatic interaction between the large π-bonded electron cloud of the benzene ring and I^‒ has an inhibiting effect on the migration of I^‒, which in turn constrains the capture of excited state electrons by Pb²⁺ and iodine vacancies. Thus, we believe that the introduction of the rational ionic liquid 1-methyl-3-benzyl-imidazolium iodide effectively enhances the short-circuit current density (J_SC) of the device, which opens a new pathway for the preparation and synthesis of new high-performance passivators.