Coupled effects of strain and halogen substitution on the structural, optoelectronic, and photovoltaic characteristics of Pb-Free Cs2AgInBr6: Density functional theory approach using HSE, BSE, and numerical methods

Abstract

The discovery of lead-free halide double perovskites ${\text{Cs}}_2{\text{AgInBr}}_6$ and ${\text{Cs}}_2\text{AgInBr}5\text{Cl}$ offers a promising avenue for the development of new absorber materials in solar cells. In this study, ab initio calculations based on density functional theory (DFT) are performed to investigate the impact of biaxial strain from +3% to -3% on the structural, optoelectronic, and photovoltaic properties of these compounds. Negative formation energies confirm their thermodynamic stability, enhanced by the partial substitution of bromine for chlorine. The band gap evolution under biaxial strain reveals high flexibility, suggesting a strong potential for adaptation to meet the requirements of targeted applications. Both structures exhibit high absorption coefficients (of the order of $10^5{\text{cm}}^{-1}$) in the UV-visible region, and their absorption spectra show a redshift and peak broadening under stress, indicating an improvement in optoelectronic efficiency. In addition, the static dielectric constant (SDC) increased depending on biaxial compressive strain for ${\text{Cs}}_2{\text{AgInBr}}_6$. Finally, The photovoltaic performances of ${\text{Cs}}_2{\text{AgInBr}}_6$ and ${\text{Cs}}_2{\text{AgInBr}}_5\text{Cl}$ show significant enhancement, particularly under the application of low compressive strain, a maximum power conversion efficiency of 25.50% is achieved for ${\text{Cs}}_2{\text{AgInBr}}_6$ under a -2% biaxial strain. These results highlight the impact of biaxial strain on the optoelectronic properties and performances of ${\text{Cs}}_2{\text{AgInBr}}_6$ and ${\text{Cs}}_2{\text{AgInBr}}_5\text{Cl}$, opening promising perspectives for their use in advanced optical devices.