Abstract
CsGeI3 has been widely studied as an important photoelectric material. Based on the density functional theory (DFT), we use first-principles to study the photoelectric properties of CsGeI3 by applying successive hydrostatic pressure. It has been found that CsGeI3 has an optimal optical band gap value of 1.37 eV when the applied pressure is −0.5 GPa, so this paper focuses on the comparative study of the photoelectric properties when the pressure is −0.5 GPa and 0 GPa. The results showed that CsGeI3 has a higher dielectric value, conductivity, and absorption coefficient and blue shift in absorption spectrum when the pressure is −0.5 GPa. By calculating and comparing the effective masses of electrons and holes and the exciton binding energy, it was found that their values are relatively small, which indicates that CsGeI3 is an efficient light absorbing material. CsGeI3 was found to be stable under both pressure conditions through multiple calculations of the Born Huang stability criterion, tolerance factor T, and phonon spectrum with or without virtual frequency. We also calculated the elastic modulus of both pressure conditions and found that they are both soft, ductile, and anisotropic. Finally, the thermal properties of CsGeI3 under two kinds of pressure were studied. It was found that the Debye temperature and heat capacity of CsGeI3 increased with the increase of thermodynamic temperature, and the Debye temperature increased rapidly after pressure, while the heat capacity slowly increased and finally stabilized. Through the calculation of enthalpy, entropy, and Gibbs free energy of CsGeI3, it was found that the Gibbs free energy decreases faster with the increase of temperature without applied pressure, which indicates that CsGeI3 has a higher stability without pressure. Through the comparative analysis of the photoelectric properties of CsGeI3 under pressure, it was found that CsGeI3 after applied pressure is a good photoelectric material and suitable for perovskite solar cells (PSCs) material.
Highlights
Organic–inorganic hybrid halide perovskites and related materials have attracted much attention in the past decade due to their high absorption coefficient, appropriate band gap width, excellent carrier mobility, long carrier life, and low cost [1,2,3,4,5,6]
The first-principles based on density functional theory (DFT) and plane wave pseudo-potential method implemented in the Cambridge Sequential Total Energy Package (CASTEP) code are used in the current calculation [26]
In order to study the effect of pressure on the electronic structure, we studied the effect of band structure and density of states (DOS) under pressure
Summary
Organic–inorganic hybrid halide perovskites and related materials have attracted much attention in the past decade due to their high absorption coefficient, appropriate band gap width, excellent carrier mobility, long carrier life, and low cost [1,2,3,4,5,6]. Recent studies have shown that they have a high photoelectric conversion efficiency (PCE) of more than 25% [7]. They have been widely used in solar cells, photon emitters, photodetectors, and other photoelectric devices [8,9,10,11]. The most used perovskite materials are organic methylammonium lead iodide and formamidinium lead iodide due to their excellent PCE. Inorganic perovskite has attracted research attention, among which Cs+
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