Surface CH₃NH₃⁺ to CH₃⁺ Ratio Impacts the Work Function of Solution‐Processed and Vacuum‐Sublimed CH₃NH₃PbI₃ Thin Films

Abstract

CH3NH3PbI3 thin films are fabricated using several representative synthesis methods such as spin‐coating, evaporation, and a combination of the two. These methods, which frequently occur in reported literatures, use the same precursors PbI2 and CH3NH3I but differ in how the two are mixed. It is found that the latter plays a vital role in determining the surface morphology, composition, and grain size of the films, even when the same stoichiometric ratio of the precursors is used. X‐ray photoelectron spectroscopy reveals that the amount of CH3+‐type defects, which results from CH3NH3I dissociation, is sensitive to both the physical state of CH3NH3I and the order of mixing sequence. The variation of the CH3NH3+:CH3+ ratio also affects the valence band and the work function of the corresponding films, as revealed by ultraviolet photoelectron spectroscopy. Furthermore, the energy‐level alignment between the perovskite film and a model hole transport layer, N,N′‐di(1‐naphthyl)‐N,N′‐diphenylbenzidine (NPB) is examined. It is found that the CH3NH3+:CH3+ ratio correlates with the offsets between the valence band maximum of perovskite film and the highest occupied molecular orbital of NPB as well, and the energy‐level alignment with the dual‐source, coevaporated CH3NH3PbI3 film is most suitable for efficient hole transport.

Defect Passivation via the Incorporation of Tetrapropylammonium Cation Leading to Stability Enhancement in Lead Halide Perovskite

“…The shift of this latter in TPA x MA 1− x PbI 3 2% stems from an upward movement of the Fermi level in the gap as a result of different punctual defect levels in the film 52,53. This shift toward ≈4.10 eV value is also interesting as it tends to suggest a lower level of p‐type defects induced by the MA + deficient perovskite in good agreement with the studies reported by Duhm and co‐workers52 Figure 3h schematizes the band diagram based on UPS measurements. The VBM position has been determined by the extrapolation of the UPS data plotted on a logarithmic scale,54,55 and is equal to 1.56 and 1.58 eV for MAPI and TPA x MA 1− x PbI 3 2%, respectively (Figure 4g).…”

“…The value of the work function for MAPI is in agreement with what has been previously reported in the literature 51. The shift of this latter in TPA x MA 1− x PbI 3 2% stems from an upward movement of the Fermi level in the gap as a result of different punctual defect levels in the film 52,53. This shift toward ≈4.10 eV value is also interesting as it tends to suggest a lower level of p‐type defects induced by the MA + deficient perovskite in good agreement with the studies reported by Duhm and co‐workers52 Figure 3h schematizes the band diagram based on UPS measurements.…”

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8MA0.2Sn0.5Pb0.5I3) for All‐Perovskite Tandem Solar Cells

“…The C 1s spectra exhibit two main peaks at ≈288.0 and ≈284.6 eV and a shoulder at ≈286 eV. These features are indicative for the organic cations of FA and MA . The sample prepared by the antisolvent method shows highest value of the organic cations on the surface while the prepared sample at vacuum time of 5 s shows the lowest C‐related intensity (Figure i).…”

“…The XPS survey spectra are shown in Figure S5 in the Supporting Information. [5,36] The sample prepared by the antisolvent method shows highest value of the organic cations on the surface while the prepared sample at vacuum time of 5 s shows the lowest C-related intensity (Figure 2i). the vacuum time.…”

Enhance the Properties of BiI3‐Based Resistive Switching Devices via Mixing Ag and Au Electrodes

“…[19] Furthermore, the nature of the substrate has been proven to have a significant effect on the morphology, stoichiometry, and electronic structure of halide perovskite, which will affect the Schottky barrier and defect density of perovskite. [29][30][31][32] Overall, the resistive switching behavior would be considerably dependent on the electrode.…”