Regulation of Luminescence Properties of the Ultrathin Two-Dimensional Halide Perovskite Cs2PbIxCl4−x (x = 0,1,2,3,4) with Ruddlesden-Popper Structure

The synthesized two-dimensional (2D) Ruddlesden-Popper (RP) all-inorganic mixed halogen perovskite, ${\mathrm{Cs}}_{2}{\mathrm{Pb}\mathrm{I}}_{x}{\mathrm{Cl}}_{4\ensuremath{-}x}$ (x = 2) has attracted extensive attention due to its excellent luminescence properties and environmental stability. However, the regulation of halogen ratio and halogen replacement sites on the luminescence properties of 2D RP inorganic mixed halogen perovskite remains unknown. In this paper, the luminescence properties containing band structures, effective mass, exciton-binding energies, photoluminescence emission energy, and the transition dipole moment of 2D RP perovskite ${\mathrm{Cs}}_{2}{\mathrm{Pb}\mathrm{I}}_{x}{\mathrm{Cl}}_{4\ensuremath{-}x}$ (x = 0,1,2,3,4) were studied via density-functional theory. To systematically represent different replacement sites, according to the halogens on the equatorial plane of the octahedron, we divide it into three types. [(1) the halogens on the equatorial plane are $\mathrm{I}$ atoms; (2) the halogens on the equatorial plane are $\mathrm{Cl}$ atoms; (3) the halogens on the equatorial plane are composed of $\mathrm{I}$ and $\mathrm{Cl}$ atoms]. The calculation results show that for structures with replacement sites of the same kind, the band gap, photoluminescence emission energy, and transition dipole moment decrease with the increase of the proportion of $\mathrm{I}$ atoms, while the opposite is true for exciton-binding energy and effective mass. In addition, among the three types of replacement sites, the quadratic eigenvalue problem-Mix (equatorial plane is composed of $\mathrm{I}$ and $\mathrm{Cl}$) type replacement site is the most conducive to the luminescence performance of the material. Our theoretical study will provide guidance for the design and fabrication of highly luminescent 2D RP perovskite.