In this report, we have studied lead-free perovskite materials A₂BCl₆ (A = Rb, Cs; B = Si, Ge, Sn) using the DFT technique. DFT-based global descriptors of perovskite materials are computed and analyzed. Our results reveal that Rb₂SiCl₆ is the most suitable material among the studied compounds for solar cell applications. Other parameters, namely, tolerance factor, optical properties, and IR and Raman spectra of A₂BCl₆, are also reported.

Abstract

In recent years, lead-free double perovskite materials have attracted much attention due to their probable applications in photovoltaic and optoelectronic devices. In this work, the electronic and optical properties of lead-free double perovskites A₂BCl₆ (A = Rb, Cs; B = Si, Ge, and Sn) are studied using density functional theory (DFT) methodology. The result shows that the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps of these compounds vary between 0.524 and 0.919 eV, which agrees with the previously reported data. HOMO-LUMO gap for Rb₂SiCl₆ is observed as 0.919 eV, which falls in the optimal energy gap range, that is, 0.9 to 1.6 eV for double perovskite material. Conceptual DFT-based descriptors—molecular hardness, softness, electronegativity, electrophilicity index, and dipole moment of these compounds—are studied. The tolerance factor of A₂BCl₆ is observed in the range of 1.00 to 1.26. Rb₂SnCl₆ is almost a perfect fit with a value of 1.00. Cs₂SiCl₆ shows the maximum value of the refractive index and dielectric constant. Optical electronegativity is found between 0.178 and 0.246 eV. The suitable band gap and high value of the refractive index and dielectric constant make double perovskites A₂BCl₆ effective for solar cells and optoelectronic devices.