Stability of triple cation halide perovskites layers: study of the chemical evolution after light soaking thanks to XPS analysis

Ageing experiments have been implemented on triple cation halide perovskites (Cs-0.05(MA(0.14), FA(0.86))(0.95) Pb (I-0.84, Br-0.16)(3)) to evaluate the stability of this competitive material for solar applications. X- ray Photoelectron Spectroscopy analyses have been realized to determine the chemical evolutions at the surface and in-depth during air ageing in dark and after light soaking. Different illumination times (up to 15 hours) have been tested to identify light soaking induced effects on the composition and on the chemical environments of the perovskite layer, by comparison with dark and pristine conditions. In particular, we show that the oxygen incorporation plays a major role in ageing mechanism.