Unmasking the magic of magic blue in perovskite doping

Abstract

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 a methylammonium lead iodide (CH₃NH₃PbI₃ or MAPI) perovskite, increases the conductivity up to 30 times and shifts the Fermi level by about 100 meV towards the valence band. The latter is confirmed via 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 occurring at grain boundaries of the polycrystalline perovskite film.