Influence of partial substitution of $Pb$ by ge atoms on the stability of $CsFAPbI_3$ hybrid perovskites to strong electron fluxes

The influence of electron flow with energy of $8.5$ MeV on the stability of perovskite $CsFAPbI_3$ with partial replacement of $1\%$ $Pb$ lead atoms by $Ge$ atoms ($CsFAPbGeI_3$) has been studied by X-ray photoelectron spectroscopy (XPS). The substitution leads to a low-energy shift of the valence band edge, which should lead to a decrease in the forbidden bandwidth of the material. $Ge$ atoms are able to occupy $Pb$ positions in the perovskite structure, but the crystal lattice is distorted. At irradiation by electrons $FA$-cation decomposition occurs, and in the chemical composition of $CsFAPbGeI_3$ in comparison with the initial $CsFAPbI_3$ the concentration of lead decreases, which indicates a change in the chemical composition of the surface layer due to the migration to the surface of the decomposition products of FA-cations and atoms of $Cs, I$ and $Ge$ removed from their positions in the perovskite grid.