Wide bandgap hybrid halide perovskites based on bromine and chlorine halide anions have emerged as potential candidates for various optoelectronic devices. However, these materials are relatively less explored than the iodine-based perovskites for microscopic details. We present experiment and first-principles calculations to understand the structural, optical, and electronic-structure of wide bandgap CH3NH3Pb(Br1-xCLx)(3) (x = 0, 0.33, 0.66, and 1) 3D hybrid perovskite materials. We substituted Br- with Cl- to tune the bandgap from 2.4 eV (green emissive) to 3.2 eV (blue (UV) emissive) of these materials. We correlate our experimental results with first-principles theory and provide an insight into important parameters like lattice constants, electronic structure, excitonic binding energy (E-X), dielectric constant, and reduced effective mass (mu(r)) Of charge carriers in these perovskite semiconductors. Electronic structure calculations reveal that electronic properties are mainly governed by Pb 6p and halide p orbitals. Our estimates of E-X within a hydrogen model suggest that an increase in E-X by increasing the Cl- (chlorine) concentration is mainly due to a decrease in the dielectric constant with x and almost constant value of mu(r) close to the range of 0.07m(e).