We use a Kramers-Kronig consistent basis-spline (B-spline) model to facilitate our appended optical dispersion data analysis. The B-spline function is a piecewise polynomial function that consists of multiple segments, each of which is defined by a set of control points and the polynomial degree. This analysis method results in a smooth and continuous function across the modeled segments, which can then be adjusted to fit the experimental data using conventional optimization algorithms. The B-spline formalism was used here to fit both the experimental spectroscopic ellipsometry and transmission data (Figure ). The modeled results in Figure show reasonable profile fits of the fine spectral features above and below the bandgap for MAPbBr3. By comparison, fitting fine spectral features is not easily done using a conventional general oscillator model approach (e.g., Gaussian, Lorentz, Tauc-Lorentz, Cody-Lorentz, or Tanguy formalisms). Our spectroscopic ellipsometry and transmission intensity appended modeling approach with a Kramers-Kronig consistent high resolution B-spline fit yields a rigorous optical dispersion data analysis of single crystal MAPbBr3.