Shape-, Size- and Composition-Controlled Lead Free Organic-Inorganic Halide Perovskites with Tunable Optical Properties

In the world of perovskite halides, the lower dimensionality is showing high structural tunability and more stability with the introduction of hydrophobic organic cations by blocking the moisture penetration in comparison to 3D structure. This result in attractive optoelectronic properties for different field of applications such as solar cells, lasers, photodetectors, memory devices and LEDs. The progress and field of applications of perovskite halides in the last decade is tremendous, however they contain toxic lead which is restricting the applications due to stability, health and ecological concerns. So, there is an urgent need to include the non-toxic elements.<br/>Here, we are reporting a new photoluminescent lead-free class of materials, BZA₃BiX₆ [BZA is benzylamine, Bi is bismuth and X is bromine and iodine]. They have been synthesized by a solution-based approach with a monoclinic structure that has isolated MX₆ octahedra surrounded by the organic cations. The powder morphology of the grown crystals is analysed by HR-SEM which concluded the layered growth. BZA₃BiBr₆and BZA₃BiI₆ exhibits semiconducting behaviour with a bandgap of 2.7eV and 2.2eV respectively. Upon 350 nm excitation, BZA₃BiBr₆ exhibits broad emission centered at 415 nm and 450 nm with a long tail. On the other hand, BZA₃BiI₆ is not an emitter. We also synthesized the intermediate perovskites and they confirmed that the iodine presence is reducing the emission prooperties. We consider them as 0D perovskite halides as the octahedral cations are completely surrounded by the organic cations. In this work we are doing a systematic study of the crystal structure, degree of distortion and its purity using the single crystal X-ray diffraction, powder X-ray diffraction, Fourier-Transform Infrared Spectroscopy (FTIR) and Raman analysis. The thermal stability of the sample has been examined by TGA/DTA analysis. The optical studies have been thoroughly studied on UV-spectrophotometer and spectrofluorometer. This study will open the doors for a new type of materials by exploring the individual sites in the structure.