Variable angle spectroscopic ellipsometry was used to measure our MAPbBr3 single crystal in a wavelength range of 210-2500 nm. These data contain changes to the amplitude ratio (Ψ, Figure ) and phase (Δ, Figure ) difference between the p-and s-reflection coefficients of the polarized incident light, but often do not provide necessary sensitivity to low absorption coefficients of a given material (i.e., α <100 cm -1 ). As a result, absorptance characteristics (especially with very fine spectral features observed for MAPbBr3) can be under approximated from spectroscopic ellipsometry characterization alone. However, appending spectroscopic ellipsometry data (Figure ) with transmission intensity data (200-2500 nm, Figure ) can provide the necessary optical absorption information to properly derive the optical properties of MAPbBr3 for both normal and anomalous optical dispersion. Furthermore, in some cases, this appended modeling approach can help improve the accuracy of the analysis and reduce uncertainties in the optical property derivation. As a result, our approach eliminates and/or corrects parameter correlations or insensitivity that could have occurred from optical dispersion data analysis using ellipsometry data alone. It is important to note that our experimentally appended optical analysis essentially yields the effective optical properties of our single crystal MAPbBr3, given the subtle oxidation at the surface of the single crystal due to the processing/handling conditions employed (see Figure ). A separate oxide layer was assessed in the optical dispersion data analysis for comparison, but resulted in negligible influence (i.e., little change to the mean squared error, MSE, of the fits) to the derived optical properties. As such, an oxide layer was not included here for simplicity of illustration. However, the influence of the oxide layer is captured in our experimentally appended optical dispersion data analysis (i.e., the impact on optical transmission is captured). Given the minimal surface oxidation, we consider these effective optical properties a close approximation of fully stoichiometric MAPbBr3. This appended modeling approach is necessary for MAPbBr3 to improve anomalous optical dispersion sensitivity to the bandgap transition regime as well as lower-order spectral overtones.