Revealing the role of Pb super(2+) in the stability of organic-inorganic hybrid perovskite CH sub(3)NH sub(3)Pb sub(1-x)Cd sub(x)I sub(3): an experimental and theoretical study

This paper presents the synthesis of organic-inorganic hybrid perovskite CH sub(3)NH sub(3)Pb sub(1-x)Cd sub(x)I sub(3). The effect of incorporating Cd super(2+) or Pb super(2+) on the stability of the perovskite structure was analysed from a theoretical and experimental viewpoint. The XRD results showed that the tetragonal perovskite structure was formed for x values of up to 0.5, which seems to indicate that the presence of a considerable amount of Pb super(2+) is necessary to stabilise the structure. In turn, UV-Vis spectroscopy showed how the presence of Cd super(2+) led to a reduction in the optical band gap of the perovskite structure of up to 9% for CH sub(3)NH sub(3)Pb sub(0. 5)Cd sub(0.5)I sub(3) with regard to the MAPbI sub(3) structure. Moreover, periodic-DFT calculations were performed to understand the effect of the increased concentration of Cd on the structural and electronic properties of MAPbI sub(3) perovskites. The analysis of both the ELF and the non-covalent interaction (NCI) index show the important role played by the Pb super(2+) ions in stabilizing this kind of hybrid perovskite structures. Finally, the DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy. The theoretical band gap values decreased as the concentration of Cd increased.