Synthesis, Structure, and Tunability of Zero-Dimensional Organic-Inorganic Metal Halides Utilizing the m -Xylylenediammonium Cation: MXD 2 PbI 6 , MXDBiI 5 , and MXD 3 Bi 2 Br 12 ·2H 2 O.

Over the past decade, the efficiency of photovoltaic devices based on CH 3 NH 3 PbI 3 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: MXD 2 PbI 6 , MXDBiI 5 , and (MXD) 3 Bi 2 Br 12 ·2H 2 O. The different structures of the new materials lead to compounds with a range of band gaps with MXDBiI 5 having the lowest at 2.15 eV. We have explored the tunabilty of MXDBiI 5 through halide substitution by preparing a series of samples with composition MXDBiI 5- x Br x and determined the halide content using energy dispersive X-ray spectroscopy. A large range of solid solution is obtained in MXDBiI 5- x Br 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.