Mixed valence Sn doped (CH3NH3)(3)Bi2Br9 produced by mechanochemical synthesis

Bismuth halides with formula A(3)Bi(2)X(9), where A is an inorganic or organic cation, show desirable properties as solar absorbers and luminescent materials. Control of structural and electronic dimensionality of these compounds is important to yield materials with good light absorption and charge transport. Here we report mechanochemical reaction of (CH3NH3)(3)Bi2Br9 with SnBr2 at room temperature in air, yielding a material with strong absorption across the visible region. We attribute this to mixed valence doping of Sn(ii) and Sn(iv) on the Bi site. X-Ray diffraction shows no secondary phases, even after heating at 200 degrees C to improve crystallinity. X-Ray photoelectron spectroscopy suggests the presence of Sn(ii) and Sn(iv) states. A similar approach to dope Sn into the iodide analogue (CH3NH3)(3)Bi2I9 was unsuccessful.