In addition to the effectiveness of these aforementioned hard X-ray tools, several of the elements involved in the PSC research have relevant XRF (X-ray fluorescence) signals in the tender or hard X-ray regime. Correa-Baena et al. performed nano-XRF and XBIC (X-ray beam induced current) measurements of (FAPbI3)0.83(MAPbBr3)0.17 with different doping concentrations of RbI where they showed that incorporation of alkali cations like Rb + onto the A-site of ABX3 structure, instead of larger organic cations, leads to an enhancement of the stability in the perovskite film. Among other synchrotron-based studies, X-ray photoemission electron microscopy (XPEEM) was employed to study surface chemistry and defect states in spatially-resolved band bending between charge transport layers and the perovskite layer.