fig2
Figure 2. XPS characterization of (A) Pb 4f and (B) I 3d regions for pristine and modified perovskite layers; (C) UPS spectra of the reference and modified perovskite films; (D) Schematic illustration of the energy level structure of the PSC device. FTAC: (Ferrocenylmethyl)trimethylammonium chloride; XPS: X-ray photoelectron spectroscopy; UPS: ultraviolet photoelectron spectroscopy; ITO: indium tin oxide; PVK: perovskite.
