Varying the halide ratio (e.g., Br^–:I^–) is a convenient approach to tune the bandgap of organic lead halide perovskites. The complexation between Pb²⁺ and halide ions is the primary step in dictating the overall composition, and optical properties of the annealed perovskite structure. The complexation between Pb²⁺ and Br^– is nearly 7 times greater than the complexation between Pb²⁺ and I^–, thus making Br^– a dominant binding species in mixed halide systems. Emission and transient absorption measurements show a strong dependence of excited state behavior on the composition of halide ions employed in the precursor solution. When excess halide (X = Br^– and I^–) are present in the precursor solution (0.3 M PbX₂ and 0.9 M CH₃NH₃X), the exclusive binding of Pb²⁺ with Br^– results in the formation of CH₃NH₃PbBr₃ perovskites as opposed to mixed halide perovskite.