Electronic structures at the interface between Au and CH3NH3PbI3

Abstract

The electronic properties of interfaces formed between Au and organometal triiodide perovskite (CH₃NH₃PbI₃) are investigated using ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES) and X-ray photoemission spectroscopy (XPS). It is found that the CH₃NH₃PbI₃ film coated onto the substrate of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/indium tin oxide (ITO) by a two-step method presents n-type semiconductor behavior, with a band gap of 1.7 eV and a valence band (VB) edge of 1.0 eV below the Fermi energy (E_F). An interface dipole of 0.1 eV is observed at the CH₃NH₃PbI₃/Au interface. The energy levels of CH₃NH₃PbI₃ shift upward by ca. 0.4 eV with an Au coverage of 64 Å upon it, resulting in band bending, hence a built-in field in CH₃NH₃PbI₃ that encourages hole transport to the interface. Hole accumulation occurs in the vicinity of the interface, facilitating the hole transfer from CH₃NH₃PbI₃ to Au. Furthermore, the shift of the VB maximum of CH₃NH₃PbI₃ toward the E_F indicates a decrease of energy loss as holes transfer from CH₃NH₃PbI₃ to Au.