Structural, Electronic, and Optical Properties of Cs2SnX4 (X = Cl, Br, and I) Multilayers: A Density Functional Theory Study

The Cs2SnX4 (X = Cl, Br, and I) halide perovskites are currently emerging as a new family of 2D materials and promising candidates for photovoltaic and optoelectronic devices. Herein, the structural, electronic, and optical properties of the Cs2SnX4 multilayers (Ms) with 1-3 layers are investigated by density functional theory (DFT). The structural properties show that the bond length variation of Cs2SnX4 is closely related to surface effects. The Cs2SnCl4 Ms have the lowest formation energies and the best stability, and the formation energies decrease and the stability improves when the number of layers increases. The electronic properties show that the direct-bandgap semiconductor Cs2SnX4 Ms bandgap values (Cl: 1.513-1.188-0.932, Br: 1.342-1.015-0.862, I: 1.198-0.903-0.729) decrease with the change from 1 to 3 layers and from Cl to I. The p orbitals of X atoms and 5p orbitals of Sn atoms are mainly involved in conduction. The optical properties indicate that Cs2SnX4 Ms achieve coverage and adjustability in the near-infrared and visible-light ranges. The calculations provide a fundamental theoretical basis for the research and application of Cs2SnX4.