Before STXM measurements: As presented earlier, the conventional ABX3 structure of the perovskites has been tinkered with heavily in order to tune band-gap, increase charge carrier mobility, minimize trap states, improve the efficiency as well as stability of these materials under working conditions. The details of these compositional engineering are beyond the scope of this paper. However, in order to assess the applicability of soft X-rays to the study of these materials it is necessary to know the various materials and their possible degradation products (as a result of external or internal stress). The various X-ray absorption edges that could be accessed within the soft X-ray regime can thus be explored. Table lists some of these materials (pure and mixed), their chemical formula and the energy of some of the relevant X-ray absorption edges. These materials degrade and decompose into various other compounds under various kinds of stress. For example, under white light illumination in the presence of oxygen, MAPbI3 has been shown to decompose into PbI2, NH3, MA, CH3I, I2 and Pb(OH)2. . Various mechanisms have been proposed for the degradation of MAPbI3 in the presence of moisture.