Pressure effects on the opto-electronic and mechanical properties of the double perovskite Cs2AgInCl6

The double perovskite Cs2AgInCl6 is a potential material for the absorbing layer of a thin film solar cell due to its direct band gap. The only current limitation the material has is its wide band gap. A careful engineering of its structural, mechanical and opto-electronic properties with the aid of hydrostatic pressure ranging from 0 GPa16 GPa has been studied using density functional theory. The calculations were carried out using GGA-PBEsol (Perdew-Burke-Ernzerhof revised for solids) exchange correlation functional. It is found that the lattice constant reduces as the pressure increases, while the bulk modulus increases as the exerted pressure increases. The bulk moduli calculated from the elastic constants are found to be in agreement with those obtained via Birch-Murnaghan equation of state. This indicates the accuracy of the calculations, and it is achieved at all pressure values. The mechanical properties of the material are investigated, and the material is found to be anisotropic and ductile at all pressure considered. Due to the underestimation of the energy band gap by GGA-PBEsol exchange correlation functional, Tran-Blaha modified Burke Johnson (TB-mBJ), a metaGGA functional, was used to calculate the electronic and optical properties. The energy band gap is found to reduce from 2.746 eV at ambient pressure to 2.482 eV at 6 GPa and momentarily increases until it reached 2.501 eV at 16 GPa. The optical properties of Cs2AgInCl6 revealed its absorption threshold is in the visible range, although a shift in the absorption threshold is observed as pressure is applied on it. An 8.7 % increase in the refractive index is observed as pressure increases. The calculated absorption coefficient corresponds reasonably with the calculated band gap. The electron energy loss function and reflectivity of the material have also been investigated.