Efforts to replace the lead-based perovskite have gain significant improvements in the last decade. Lead free double halide perovskite are being considered to replace the toxic lead-based perovskite materials for solar cell applications. Density functional theory (DFT) and linear response time-dependent density functional theory (TDDFT) are used in this study to simulate and investigate the effect of vacancy in the Indium (In) site of leadfree double halide perovskite A2BB′X6 (A = Cs; B = In, B′ = Sb; X = Cl) on the structural, electronic, and optical properties for possible solar cell application. On the structural properties, the total bond length of the material Cs2InSbCl6 was found to be 30.3848 Å and the creation of the indium vacancy raises the value to 30.594 Å. The bulk modulus of Cs2InSbCl6 was calculated to be 28.44 Gpa and 26.22 Gpa for Cs2In-xSbCl6. The calculated band structure for Cs2InSbCl6 reveals semiconducting behavior with a direct energy band gap of 0.99 eV along 𝛤 point symmetry while the created indium vacancy band structure reveals metallic behavior with an overlap of electronic states along the Γ - W – Γ symmetry. The result of the optical properties calculations shows that the material Cs2InSbCl6 has higher absorption coefficient, low refractive index, low reflectivity and higher conductivity when compared to the created indium vacancy material.