Halide double perovskite Rb2AgBiX6 (X = Br, Cl) exhibits excellent stability and optical properties under high pressure

Abstract

In recent years, halide double perovskite materials have shown great potential in the photovoltaic field due to high stability and low toxicity. This study uses first principles calculations to systematically explore the structural, mechanical, electronic, and optical properties of Rb₂AgBiX₆ (X = Br, Cl) under high pressure. Elastic calculations show that our perovskite material Rb₂AgBiX₆ (X = Br, Cl) has strong resistance to shear deformation and longitudinal tension under high pressure, and can further enhance its mechanical properties and stability under pressure. The equilibrium bandgaps of Rb₂AgBiBr₆ and Rb₂AgBiCl₆ are 1.30 eV and 1.81 eV (both indirect), and they turn into metallic phases at 40 GPa and 70 GPa, respectively. Optical property calculations show that as pressure increases, the optical response of the material increases, and at the same pressure, the optical performance of Rb₂AgBiBr₆ is superior to that of Rb₂AgBiCl₆. This is because the lattice distortion induced by high pressure leads to band reconstruction, reduces the effective mass of electrons and holes, and improves carrier mobility. The increase in carrier mobility helps to reduce the probability of electron hole pair recombination and enhance optical performance. The larger ionic radius of Br⁻ exhibits more significant bandgap closure and band curvature changes under high pressure, resulting in a greater reduction in effective mass and ultimately exhibiting better optoelectronic performance under the same pressure. This study provides theoretical predictions for the high-pressure performance of these materials and valuable references for their application under extreme conditions.