Analysis of the structural, electronic, optical and mechanical properties of CsGeI2Br under tensile and compressive strain for optoelectronic applications: A DFT computational perspective

Abstract

In this work, the impact of triaxial strain on the structural, optoelectronic and mechanical properties of CsGeI₂Br is thoroughly investigated, with a particular emphasis on its applicability in optical technologies spanning the visible and ultraviolet spectra. This research fills a notable gap in the literature, highlighting the intriguing properties of this material under external strain. First, the unstrained CsGeI₂Br is identified as a direct band gap semiconductor, revealing an energy gap of 0.714 eV. Moreover, the obtained results show a remarkable sensitivity of CsGeI₂Br's band gap to triaxial strain. Under a triaxial deformation ranging from −6% to 6 %, the energy of the bandgap undergoes a remarkable transformation, varying from 1.81 eV under tensile stress to 0.101 eV under compressive strain; The material approaches the metallic state under compressive strain and exhibits increased bandgap energy under tensile stress. Furthermore, the investigation delves into the optical coefficients in both x = y, z directions, revealing that triaxial strain can significantly enhance absorbance, particularly within the visible and ultraviolet energy spectra. Additionally, triaxial strain introduces significant anisotropy and influences the optical band gap. This results in increased absorption capacity and optical conductivity under tensile stress, making it more effective and better suited for various optical applications, including surgical tools, integrated circuits, QLED, OLED, solar cells, waveguides, and materials for solar heat reduction. The mechanical stability of CsGeI₂Br across the entire range of applied strain is validated by the elastic constants, which impeccably adhere to stability criteria. The negative cohesive energy values determined for unconstrained and constrained CsGeI₂Br signify their thermodynamic stability, establishing their experimental feasibility. Compression strain significantly influences the mechanical properties, enhancing the ductility of this compound.