Overall, these modeled PSC designs demonstrate the critical influence of accurate optical property determination in order to further improve the optical performance of modeled PSC devices. Most influential for these illustrative planar thin film device designs is capturing MAPbBr3 optical behavior at the band edge transition and below. Also present in each of these designs (Table and Figure ) is the influence of the MA overtones of MAPbBr3. It is also important to note that the influence of these spectral features at the reported layer thicknesses (Table ) are subtle but not negligible, and these can impact optical performance below the bandgap. Such material optical characteristics have the potential to yield unexpected optical or device behavior if unaccounted for in the given PSC optical coating design (i.e., R, T, and A including the performance at different angles of incidence). The impact of such features will become more significant with increased MAPbBr3 layer thicknesses due to an increase in solar radiation attenuation.