Synthesis, structure and tunability of zero dimensional organic-inorganic metal halides utilising the m-xylylenediammonium cation: MXD₂PbI₆, MXDBiI₅, and MXD₃Bi₂Br₁₂·2H₂O

Over the past decade, the efficiency of photovoltaic devices based on CH₃NH₃PbI₃ have dramatically increased. This has driven research efforts in all areas, from the discovery of materials to film processing to long-term device stability studies. Here, we report the synthesis and structure of three new “zero dimensional” organic–inorganic metal halides which use the meta-xylylenediammonium (MXD) cation: MXD₂PbI₆, MXDBiI₅, and (MXD)₃Bi₂Br₁₂·2H₂O. The different structures of the new materials lead to compounds with a range of band gaps with MXDBiI₅ having the lowest at 2.15 eV. We have explored the tunabilty of MXDBiI₅ through halide substitution by preparing a series of samples with composition MXDBiI₅–_xBr_x and determined the halide content using energy dispersive X-ray spectroscopy. A large range of solid solution is obtained in MXDBiI_5–xBr_x, resulting in the formation of single-phase materials for bromine contents from x = 0 to 3.71 (iodine contents from 1.29 to 5). This highlights the fact that zero-dimensional organic–inorganic halides are highly tunable, in a similar manner to the higher-dimensional perovskite counterparts. Such new materials open up the opportunity for further studies of the physics and optoelectronic properties of these materials.