Impact of SnF2 addition on the chemical and electronic surface structure of CsSnBr3

We report on the chemical and electronic structure of cesium tin bromide (CsSnBr3) and how it is impacted by the addition of 20 mol% tin fluoride (SnF2) to the precursor solution, using both surface-sensitive lab-based soft x-ray photoelectron spectroscopy (XPS) and near-surface bulk-sensitive synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES). To determine reproducibility and reliability of conclusions, several (nominally identically-prepared) sample sets were investigated. The effects of deposition reproducibility, handling, and transport are found to cause significant changes in the measured properties of the films. Variations in the HAXPES derived compositions between individual sample sets were observed, but in general they confirm that the addition of 20 mol% SnF2 improves coverage of the titanium dioxide substrate by CsSnBr3 and decreases the oxidation of SnII to SnIV, while also suppressing formation of secondary Br and Cs species. Furthermore, the (surface) composition is found to b...