Tuning electronic and optical properties by sublattice mixing of Cs₂AgBiCl₆for solar cell application: High-throughput screening from first-principles.

The lead-free double perovskite material (viz. Cs₂AgBiCl₆ ) has emerged as an efficient and environmentally friendly alternative to organic-inorganic hybrid lead halide perovskites. However, Cs₂AgBiCl₆ is optically inactive in the visible region owing to its large indirect band gap. To make Cs₂AgBiCl₆ optically active in the visible region of the solar spectrum, band gap engineering approach has been undertaken. Using Cs₂AgBiCl₆ as a host, bandgap and optical properties of Cs₂AgBiCl₆ have been modulated by alloying with M(I), M(II), and M(III) cations at Ag-/Bi-sites. Here, we have employed density functional theory (DFT) with suitable exchange-correlation functionals in light of spin-orbit coupling (SOC) to determine the stability, band gap, and optical properties of different compositions, that are obtained on Ag-Cl and Bi-Cl sublattices mixing. On analyzing 64 combinations within Cs₂AgBiCl₆, we have identified 19 promising configurations having band gap optimum to solar cell applications. The most suitable configurations with Ge(II) and Sn(II) substitutions have spectroscopic limited maximum efficiency (SLME) of 32.08% and 30.91%, respectively, which are apt for solar cell absorber.