Designing Two-Dimensional Properties in Three-Dimensional Halide Perovskites via Orbital Engineering

Manipulating the orbital hybridization between the metal cation and the halide anion to achieve novel properties is highly desired. Here, we present an orbital engineering strategy to construct two-dimensional (2D) electronic structures in three-dimensional (3D) halide perovskites by rationally controlling the hybridization between the d orbitals of the metal cations and the halide p orbitals. Taking Cs2Au(I)Au(III)I-6 as an example, we demonstrate that the flat conduction band and valence band at the band edges can be achieved simultaneously by combining two metal cations with different d orbital configurations using first-principles calculations. The band structure and predicted carrier mobilities show huge anisotropy along in-plane and out-ofplane directions, confirming the 2D electronic properties. In addition, the strong anisotropic optical and mechanical properties (e.g., 2D-like properties) are also presented. Our work provides orbital engineering guidance for achieving low-dimensional properties with strong anisotropy in 3D halide perovskites for novel electronic and photonic applications.