Fig. 2

Material characterization of perovskite films. a XRD patterns. A peak at 12.5° that arises from the (001) lattice planes of hexagonal (2 H polytype) PbI₂ is shown in the inset. b Fourier transform infrared (FTIR) spectra. c Time-resolved photoluminescence measurements of the pristine (control) and modulator-containing (N, S, and SN) perovskite films. The arrows in b indicate the stretching vibration peak of C = S in the films, and the dashed lines in c show the fits of the experimental data to Eq. (3). d X-ray photoelectron spectroscopy of the perovskite films in the absence (control) and presence of molecular modulators (N, S, and SN). The binding energies at approximately 138 eV and 142.5 eV in d denote the signals for Pb(II) species resulting from interfacial decomposition, such as PbO, whereas the predominant Pb 4 f signals can be ascribed to unsaturated Pb²⁺ surface ions^35,36