Solvent-Controlled Densification and Ligand Redistribution in CsPbBr 3 Nanocrystal Thin Films Revealed by Quantitative XPS and Spectroscopic Ellipsometry

Understanding and controlling nanocrystal film formation is essential for achieving uniform and electronically well-defined perovskite thin films for optoelectronic device applications. Here, we quantitatively examine how solvent volatility affects densification, porosity, and ligand redistribution in spin-coated CsPbBr 3 nanocrystal films. Using time-resolved spectroscopic ellipsometry and X-ray photoelectron spectroscopy (XPS), we track the evolution of perovskite cores, ligands, and solvents during drying. Octane-cast films densify gradually, showing ∼25% thickness reduction and increased refractive index, while hexane-cast films retain porosity due to rapid evaporation. XPS reveals preferential oleylamine retention, a ligand-rich surface, and accumulation of PbBr 2 and carbon species at the outermost interface.