Abstarct: With the introduction of solar cells and the photovoltaic properties of the world, it began a wide range of activities to provide energy for the use of sunlight. One group of these solar cells is perovskite solar cells. Lead-baxsed solar cells are very efficient, but due to the toxicity of lead, many non-toxic solar cells have been introduced. Accordingly, in this study, we introduced lead-free perovskite solar cells, bismuth-baxsed solar cell . Bismuth, which is one of the mextal elements of the fifth group and has a similar structure to Pb2 + in terms of electron arrangement with one more electron difference in P orbital and ionic radius (Pb2+ = 1.19 Å, Bi3+ = 1.03Å), therefore makes it possible to In the crystal structure, halide perovskites act to manipulate optical properties and are a good substitute for lead. The structure of A3B2X9 is that the monovalent cation A consists of Cs+, MA+ and the trivalent cation Bi3+, Sb3+ and the monovalent halide I-, Br-, Cl-, which in this study using the theoretical method of density function (DFT) and GGA approximation with The SIESTA computational code studies optical properties such as dielectric function, refractive index, absorption, reflectance, and conductivity, as well as electronic properties such as band structure, DOS and PDOS , Lattice constant of Cs3Bi2I9, MA3Bi2I9, and Cs3Bi2Br9 structures and Replacement of methyl ammonium at site A and indium at site B for band gap engineering adding indium reduces the band gap and MA increases the band gap, but at the same time improves the optical properties, especially the optical absorption of the structure.