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–xBrx and determined the halide content using energy dispersive X-ray spectroscopy. A large range of solid solution is obtained in MXDBiI5–xBrx, 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.