Revealing the role of Pb2+ in the stability of organic–inorganic hybrid perovskite CH3NH3Pb1−xCdxI3: an experimental and theoretical study

Abstract

This paper presents the synthesis of organic–inorganic hybrid perovskite CH₃NH₃Pb_1−xCd_xI₃. The effect of incorporating Cd²⁺ or Pb²⁺ 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 Pb²⁺ is necessary to stabilise the structure. In turn, UV-Vis spectroscopy showed how the presence of Cd²⁺ led to a reduction in the optical band gap of the perovskite structure of up to 9% for CH₃NH₃Pb_0.5Cd_0.5I₃ with regard to the MAPbI₃ structure. Moreover, periodic-DFT calculations were performed to understand the effect of the increased concentration of Cd on the structural and electronic properties of MAPbI₃ perovskites. The analysis of both the ELF and the non-covalent interaction (NCI) index show the important role played by the Pb²⁺ 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.