Electronic and optical properties of lead‐free double perovskites A2BCl6 (A = Rb, Cs; B = Si, Ge, Sn) for solar cell applications: A systematic computational study

Abstract

AbstractIn 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.