fig2

Figure 2. XPS energy spectra of FA_0.95Cs_0.05PbI₃ perovskite thin films before and after DMF passivation. High resolution (A) Pb 4f, (B) FTIR spectra of films; (C) TRPL for control and DMF-treated perovskite films; (D) UPS energy spectra of secondary electron cutoff region and (E) Fermi energy cutoff region; (F) Interaction diagram between DMF and FA_0.95Cs_0.05PbI₃; (G) Energy level diagram of perovskite films before and after DMF passivation. DMF: N,N-dimethylformamide; E_CB: conduction band energy; E_F: Fermi energy; E_VB: valence band energy; XPS: X-ray photoelectron spectroscopy; FTIR: Fourier transform infrared; TRPL: time-resolved photoluminescence.