Here, spectral overtones refer to the presence of other optically absorbing species in the perovskite material. While some have suggested perovskites are nearly transparent in the infrared regime this is not the case for hybrid organic-inorganic perovskites. Although not phenomenologically quantified with respect to material species and optical absorption mechanics, in the case of MAPbBr3, the MA moieties represent compositional species that contribute to the optical absorptance peaks below the band edge. For example, we observe spectral overtone features beginning at ~1050 nm that continue to longer wavelengths shown in the transmission intensity spectra in Figure . To generate a robust derivation of MAPbBr3 optical properties, it is necessary to include these anomalous optical dispersion characteristics at, above, and below the bandgap in the optical dispersion data analysis. To our knowledge, no complementary modeling methodology has been reported for MAPbX3; however, this characterization approach has been demonstrated for other complex index thin films with anomalous optical dispersion. In part, the lack of such complementary analysis for MAPbBr3 to date may be due to limited single crystal material/surface quality and sample size dimensions necessary to generate low scattering transmission intensity spectra.