Red shift of lead-free halide perovskite RbCaCl3 under pressure for enhancing optoelectronic performance

This study focuses on the exploration of pressure effects on the structural, electronic, optical, and mechanical properties of a cubic halide perovskite RbCaCl3 using density functional theory. The calculated values of lattice constant and unit cell volume at zero pressure are justified by the previous experimental and theoretical studies. As pressure is applied both the lattice constant and unit cell volume decrease steadily because of bond length reduction inside the material. The indirect band gap nature of the studied perovskite transforms into direct under applied pressure of 40 GPa and more. Moreover, the band gap value significantly reduces under pressure effect from ultraviolet to visible energy region. Though the bonding nature of both Rb-Cl and Ca-Cl is initially ionic, the induced pressure slightly reduces the ionicity of Rb-Cl and makes the Ca-Cl bond covalent. The optical absorption reveals a red shift in the visible energy region advantageous for using RbCaCl3 in solar cell applications. In addition, the overall optical analysis reveals that the pressure-induced compound is more suitable for optoelectronic device applications than that of zero pressure system. The external hydrostatic pressure significantly affects the mechanical properties of titled compound, making it more ductile and anisotropic.