Impact of Applied Pressure on the Mechanical, Opto-Electronic, and Thermoelectric Properties of Lead-Free Germanium-Based Perovskites InGeX3 (X = Cl or Br) for High-Efficiency Photovoltaic Applications

Abstract

Lead halide perovskites possess notable physiochemical characteristics and exhibit high-power conversion efficiencies. However, their commercial feasibility could be improved by stability and toxicity issues. Therefore, there is growing interest in developing stable lead-free alternatives that provide similar optical and electrical features. Perovskite solar cells that are free of lead frequently demonstrate reduced power conversion efficiency. Applying hydrostatic pressure to these compounds is used to alter their physical properties by improving their performance and uncovering important connections between their structure and attributes. This study utilizes Density Functional Theory (DFT) to examine the structural, electrical, optical, and elastic characteristics of non-toxic InGeCl₃ and InGeBr₃ halide perovskite compounds at different hydrostatic pressures, ranging from 0 to 8 GPa. The derived structural parameters closely correspond to those reported in prior investigations, hence confirming the veracity of the current findings. When subjected to pressure, the bonds between In-X and Ge-X atoms experience a decrease in length and become stronger. Electronic property assessments indicate that both compounds exhibit characteristics of direct band-gap semiconductors. As pressure increases, the band gap decreases in a straight line, moving towards a metallic state. Additionally, the pressure causes the electrical density of states around the Fermi level to increase by pushing valence band electrons upwards. The dielectric constant, absorption, and reflectivity values exhibit a progressive rise as pressure increases, while the absorption spectra move towards longer wavelengths. The results indicate that InGeCl₃ and InGeBr₃ compounds have enhanced utility for optoelectronic applications when subjected to pressure. Furthermore, the examination of the mechanical characteristics indicates that all InGeX₃ compounds exhibit mechanical stability when pressure increases. This implies that these compounds can be adjusted and utilized more effectively in optoelectronic devices and photovoltaic cells.