Structural and Optoelectronic Properties of Two-Dimensional Ruddlesden–Popper Hybrid Perovskite CsSnBr3

Abstract

Ultrathin inorganic halogenated perovskites have attracted attention owing to their excellent photoelectric properties. In this work, we designed two types of Ruddlesden–Popper hybrid perovskites, Csn+1SnnBr3n+1 and CsnSnn+1Br3n+2, and studied their band structures and band gaps as a function of the number of layers (n = 1–5). The calculation results show that Csn+1SnnBr3n+1 has a direct bandgap while the bandgap of CsnSnn+1Br3n+2 can be altered from indirect to direct, induced by the 5p-Sn state. As the layers increased from 1 to 5, the bandgap energies of Csn+1SnnBr3n+1 and CsnSnn+1Br3n+2 decreased from 1.209 to 0.797 eV and 1.310 to 1.013 eV, respectively. In addition, the optical absorption of Csn+1SnnBr3n+1 and CsnSnn+1Br3n+2 was blue-shifted as the structure changed from bulk to nanolayer. Compared with that of Csn+1SnnBr3n+1, the optical absorption of CsnSnn+1Br3n+2 was sensitive to the layers along the z direction, which exhibited anisotropy induced by the SnBr2-terminated surface.

Dimension-Dependent Bandgap Narrowing and Metallization in Lead-Free Halide Perovskite Cs3Bi2X9 (X = I, Br, and Cl) under High Pressure

“…Such a property improves the PCE of solar cells and the luminous efficiency. The absorption coefficient is usually described by the dielectric function according to the following expression [46]:…”

Electronic Structures and Photoelectric Properties in Cs3Sb2X9 (X = Cl, Br, or I) under High Pressure: A First Principles Study

“…The optical absorption coefficient of perovskite is usually expressed by the complex dielectric function, i.e., ε(ω) = ε 1 (ω) + iε 2 (ω), where ω is the frequency of the incident light and ε 1 (ω) and ε 2 (ω) are the real and imaginary parts of the complex dielectric function, respectively. Generally, ε 1 (ω) and ε 2 (ω) are used to describe the refractive and absorption behavior, respectively, which are given by the following equations [ 39 , 40 ]: where P is the principal value of the integral, V represents a unit volume, e is the electron charge, p represents the momentum transition matrix, and kn and kn ′ are the wave functions of the conduction band and valence band, respectively. The absorption coefficient, α, can be obtained by calculating the real and imaginary parts of the dielectric function [ 40 ]: …”

“…Generally, ε 1 (ω) and ε 2 (ω) are used to describe the refractive and absorption behavior, respectively, which are given by the following equations [ 39 , 40 ]: where P is the principal value of the integral, V represents a unit volume, e is the electron charge, p represents the momentum transition matrix, and kn and kn ′ are the wave functions of the conduction band and valence band, respectively. The absorption coefficient, α, can be obtained by calculating the real and imaginary parts of the dielectric function [ 40 ]: …”

Bandgap lowering in mixed alloys of Cs3Bi2−xSbxBr9 perovskite powders

“…In the Cs 3 Bi 2 Br 9 and Cs 3 Bi 2 Cl 9 perovskites, two octahedrons share one X atom (X = Br or Cl), while in the Cs 3 Bi 2 I 9 perovskite, two octahedrons share three X atoms. 3,[9][10][11][12] In this way, the Cs 3 Bi 2 I 9 , Cs 3 Bi 2 Br 9 , and Cs 3 Bi 2 Cl 9 perovskites can be referred to as zerodimensional, two-dimensional, and one-dimensional perovskites, respectively. The one-dimensional perovskite consists of an isolated MX 6 octahedron, the two-dimensional perovskite consists of a layered structure, and the zero-dimensional perovskite consists of an isolated dimer.…”

“…People have attempted to improve the optoelectronic application of Cs 3 Bi 2 Br 9 by combining DFT and experimental methods. 10,11,20 Geng et al 20 used a simple pressurization method to tune the bandgap of Cs 3 Bi 2 Br 9 while considering that when Cs 3 Bi 2 Br 9 releases pressure, the material will return to its original state. Meanwhile, doping is a useful technique for modifying the bandgap of materials.…”