Sources of Pb(0) artefacts during XPS analysis of lead halide perovskites

X-ray Photoelectron spectroscopy (XPS) spectra of methyl ammonium lead halide perovskite films typically show the presence of lead as Pb(II), but Pb(0) is also often observed, potentially influencing the interpretation of the device physics. In this article the reproducible evolution of Pb(0) peaks which are likely artefacts generated under typical XPS analytical conditions are demonstrated from methyl ammonium lead halide films that contain no Pb(0) initially. The evolution of Pb(0) occurs via (1) X-ray photolysis under typical analytical conditions and (2) alongside other chemical changes as a result of film aging in air. In both cases we note the presence of PbI2 as a common factor contributing to in situ reactions to generate Pb(0) artefacts. Hence the observation of Pb(0) should be treated with extreme caution and here we recommend simple precautions to ensure materials analysis of these films gives reliable information when analyzed under UHV conditions.