Investigation of stability and ammonia gas sensing performance of two-dimensional (2D) lead halide perovskite

Perovskite materials have a great deal of interest because of their exceptional capabilities for gas detection. The importances of perovskite are for applications of gas sensor, light absorber, solar cell, optoelectronic device and so on. Despite the enormous attention given to lead (II) iodide perovskite, the material’s stability is a major issue that urgently needs attention upon specific applications. This study was conducted to propose new 2D lead-based perovskite materials, investigate the material's stability under certain conditions, and test its potential for ammonia gas sensing. A novel 2D perovskite containing long alkyl methacrylate derivatives was synthesised based on double immersion in the material solution followed by spin-coating, and in the same time, the conventional 3D perovskite of methylammonium iodide perovskite was prepared for comparison. The physical properties of both materials were analysed based on surface morphology, surface roughness and crystallinity to find out that stability changed over time under different conditions which are room-temperature, silica and vacuum. Room-temperature is found to be the best storage for 2D material compared to silica and vacuum storage, highlighting the hydrophobicity of the material is moisture- resistance. However, the findings showed that 3D material still needs a moderate amount of water for crystallisation, which silica is the best storage condition. After ammonia gas exposure, a new XRD peak was identified as ammonium lead iodide (NH4PbI3), with a red-shifted perovskite peak (101) being observed for the case of 2D, indicating a reaction occurred and altered the crystalline structure. AFM results showed changes in surface roughness, in which 2D material exhibited a rougher surface, facilitating more adsorption sites for ammonia gas molecules. Further, the electrical properties and sensitivity were conducted to check the average sensitivity, indicating that 2D material has better ammonia gas of sensitivity than that of 3D material. In conclusion, the overall findings highlight that 2D material exhibits better stability, as if it possesses hydrophobicity properties, however, the instability of 3D material towards moisture suggests that silica storage is the optimum condition. Regarding the gas sensing application, 2D performed better than 3D materials, considering its adsorption sites for ammonia molecules. It is recommended to explore the material properties of post-effects due to gas exposure in order to explore their promising gas sensor potential.