Signi cant interests have been drawn to organic-inorganic hybrid double perovskites towards the commercialization of Pb-free non-toxic perovskites because of their unique optoelectronic properties than their inorganic counterparts. In this study, the structural, electronic and optical properties as well as stability of (CsMA)NaSbX 6 (MA= methylammonium; X= Cl, Br, I) were investigated using rst-principles density functional theory (DFT). Results of the DFT method reveal that the investigated compounds have tunable bandgaps, high absorption coe cients and high refractive indices. Findings also show that the iodide-based compound, (CsMA)NaSbI 6 shows superior optoelectronic properties compared to the bromide and chloride-based compounds, (CsMA)NaSbBr 6 and (CsMA)NaSbCl 6 . Speci cally, results of the study predict the (CsMA)NaSbI 6 organic-inorganic hybrid double perovskite to be a promising candidate for optoelectronic applications due to its high absorption coe cient (in the order of 10 6 cm -1 ), dielectric constant (approx.4.43), imaginary part of the refractive index (2.83) as well as the high formation energy depicting its stability. These results can be utilized for synthesis of sustainable and non-toxic optoelectronic devices.

Significant interests have been drawn to organic-inorganic hybrid double perovskites towards the commercialization of Pb-free non-toxic perovskites because of their unique optoelectronic properties than their inorganic counterparts. In this study, the structural, electronic and optical properties as well as stability of (CsMA)NaSbX6(MA= methylammonium; X= Cl, Br, I) were investigated using first-principles density functional theory (DFT). Results of the DFT method reveal that the investigated compounds have tunable bandgaps, high absorption coefficients and high refractive indices. Findings also show that the iodide-based compound, (CsMA)NaSbI6 shows superior optoelectronic properties compared to the bromide and chloride- based compounds, (CsMA)NaSbBr6 and (CsMA)NaSbCl6. Specifically, results of the study predict the (CsMA)NaSbI6 organic-inorganic hybrid double perovskite to be a promising candidate for optoelectronic applications due to its high absorption coefficient (in the order of 106cm-1), dielectric constant (approx.4.43), imaginary part of the refractive index (2.83) as well as the high formation energy depicting its stability. These results can be utilized for synthesis of sustainable and non-toxic optoelectronic devices.