Pressure-induced structural, electronic, optical, and mechanical properties of lead-free GaGeX3 (X = Cl, Br and, I) perovskites: First-principles calculation

Abstract

Researchers are now focusing on inorganic halide-based cubic metal perovskites that are not toxic as they strive to commercialize optoelectronic products and solar cells derived from perovskites. This study explores the properties of new lead-free compounds, specifically GaGeX₃ (where X = Cl, Br, and I), by executing first-principles Density Functional Theory (DFT) to analyze their optical, electronic, mechanical, and structural characteristics under pressure. Assessing the reliability of all compounds is done meticulously by applying the criteria of Born stability and calculating the formation energy. As discovered through elastic investigations, these materials showed anisotropic behavior, flexibility, and excellent elastic stability. The electronic band structures, calculated using both HSE06 and GGA-PBE functionals at 0 GPa, reveal fascinating behavior. However, computed band structures with non-zero pressures using GGA-PBE. Here, the conduction band moved to the lower energy when the halide Cl was changed with Br or I. In addition, the application of hydrostatic pressure can lead to tunable band gap properties in all compounds such as from 0.779 eV to 0 eV for GaGeCl₃, from 0.462 eV to 0 eV for GaGeBr₃ and from 0.330 eV to 0 eV for GaGeI₃, resulting transformation from semiconductor to metallic. Understanding the origins of bandgap changes can be illuminated by examining the partial and total density of states (PDOS & TDOS). When subjected to pressure, all the studied compounds showed an impactful increase in absorption coefficients and displayed exceptional optical conductivity in both the visible and UV zones. Yet, GaGeCl₃ is a more effective UV absorber because it absorbs light more strongly in the UV area. Moreover, GaGeI₃ stands out among the compounds examined due to its impressive visible absorption and optical conductivity, which remain consistent under varying pressure conditions. Besides, GaGeI₃ exhibits higher reflectivity when subjected to pressure making them suitable for UV shielding applications. At last, these metal cubic halide perovskites without lead present promising opportunities for advancing optoelectronic technologies. With their tunable properties and favorable optical characteristics, these materials are highly sought after for their potential in solar cells, multi-junctional solar cells, and different optoelectronic functions.

Keywords: Band gap; DFT; Density of states; Elastic stability; Optoelectronics; Renewable energy; Solar cell.

Fig. 1

This diagram illustrates the ABX₃ structure, accompanied by the supercell of GaGeX₃ (X = Cl, Br, and I) metal cubic halide perovskites.

Fig. 2

Investigating the lattice constant of GaGeX₃ (X = Cl, Br, and I) compounds with the impact of pressures.

Fig. 3

Investigating the impact of pressure on GaGeX₃ (X = Cl, Br, and I) compounds' formation energy.

Fig. 4

Band gap value of GaGeX₃ (where X = Cl, Br, and I) changes based on the pressure.

Fig. 5

Using the GGA-PBE and HSE06 functional, calculations of the electronic band structures of (a) GaGeCl₃, (b) GaGeBr₃, and (c) GaGeI₃.

Fig. 6

Pressure-driven real component of GaGeX₃'s dielectric constant (where X = Cl, Br, and I).

Fig. 7

Calculating how pressure affects the dielectric's imaginary component of GaGeX₃ (X = Cl, Br, and I) compounds.

Fig. 8

Illustrated the absorption spectra of GaGeX₃ (where X = Cl, Br, and I) with energy under pressure.

Fig. 9

Pressure-induced optical absorption of GaGeX₃ concerning wavelength, where X is equal to Cl, Br, and I.

Fig. 10

Exploring the conductivity spectra of GaGeX₃ compounds (X = Cl, Br, and I) with energy.

Fig. 11

Exploring the variations in conductivity at different wavelengths while studying the effects of different pressures on GaGeX₃ compounds (with X being Cl, Br, and I).

Fig. 12

The optical reflectivity of GaGeX₃ (where X = Cl, Br, and I) induces by pressure.

Fig. 13

Exploring the refractive index of GaGeX₃ (X = Cl, Br, and I) with applied pressure.

Fig. 14

Elastic constants of C₁₁, C₁₂, and C₄₄ for GaGeX₃ (X = Cl, Br, and I) vary with pressure.

Fig. 15

Investigating the Young's, Shear, and Bulk Modulus of GaGeX₃ (X = Cl, Br, and I) with variation of pressure.

Fig. 16

Examining the changes in Cauchy pressure, Pugh's, and Poisson's ratio of cubic GaGeX₃ (X = Cl, Br, and I) at different pressures.

Fig. 17

Investigating the impact of pressure on the hardness and machinability index of GaGeX₃ (X = Cl, Br, and I).