Probing the chemistry of perovskite systems by XPS and GD-OES depth-profiling: Potentials and limitations

The capabilities of XPS and GD-OES profiling have been evaluated on a half-cell constituted of glass / FTO / c-TiO2 / m-TiO2 / triple cation halide perovskites (Cs-0.05(MA(0.14), FA(0.86))(0.95) Pb (I-0.84, Br-0.16)(3)), focusing on metrological aspects. The validity of the chemical information measured by those destructive techniques is accurately studied, considering the possible modification inherent to the techniques themselves: X-Ray illumination, UHV, bombardment by Ar ions (mono or polyatomic). XPS and GD-OES have shown similar trends for the composition profiles. But the conditions employed for XPS profiling lead to a systematic reduction of lead, which could not be avoided as well as the organic part degradation and iodine loss. Nevertheless, differences of XPS depth profiles obtained using either Ar+ or Ar-n(+) have raised the question of the bombardment effect on the perovskite surface, influencing the reliability of the collected chemical information. The chemical and morphological study of the XPS and GD-OES crater is presented. The possibility to combine those two techniques for an advanced chemical characterization of perovskite stacks is discussed.