For many years, band gap engineering through defects has been used to develop an efficient photocatalyst. The transparent semiconductor tin oxide (SnO2) has been investigated in many research as it has various applications in optical materials due to its transparency, solar cells, biochemical applications, and in catalysis. The electronic along with optical characteristics of co-doping SnO2 were studied using first principal calculations utilizing the Density functional theory (DFT) with the Generalized Gradient Approximation (GGA) and the Perdew-Burke-Ernzerhof exchange function (PBE). Zinc, Bismuth and Indium have been introduced to the SnO2 primitive cell as defects in the material with a concentrations X 0.167 Sn 0.833 O 2-y N y where X is (Zn, Bi and In), Y is the concentration of the nitrogen doping which is 0.167. The influence of dopants on the optical and electrical characteristics of SnO2 was examined in depth after the unit cells were optimized. The study recommends the using of the Bi based tin oxide to be used as a photo catalyst among the investigated structures as it has a band gap near the 1.174 eV and high absorption in the visible light region, low exciton binding energy and smallest D ratio that leads to an enhanced photocatalytic activity compared to the pure SnO2.