The broader utilization of perovskite semiconductors in electronic devices is constrained by the inherent challenge of doping these materials. Magic Blue (tris(4-bromophenyl) ammoniumyl hexachloroantimonate) is a cationic salt which, once introduced in a polycrystalline film of methylammonium lead iodide (CH 3 NH 3 PbI 3 or MAPI) perovskite, increases by a maximum 30-fold conductivity and shifts the Fermi level by about 100 meV towards the valence energy. The latter is confirmed by surface potential measurements using Kelvin probe and ultraviolet photoelectron spectroscopy. The photoluminescence quenching of the doped samples confirms the presence of an excess of free charge carriers, while the optical bandgap remains unchanged. The doping mechanism most likely resembles molecular charge transfer doping, with the electron transfer from MAPI to the ammoniumyl cation residing at grain boundaries of the polycrystalline perovskite film.