Interfacial electronic structure at the CH3NH3PbI3/MoOx interface

Interfacial electronic properties of the CH3NH3PbI3 (MAPbI(3))/MoOx interface are investigated using ultraviolet photoemission spectroscopy and X-ray photoemission spectroscopy. It is found that the pristine MAPbI(3) film coated onto the substrate of poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate)/indium tin oxide by two-step method behaves as an n-type semiconductor, with a band gap of similar to 1.7 eV and a valence band edge of 1.40 eV below the Fermi energy (E-F). With the MoOx deposition of 64 angstrom upon MAPbI(3), the energy levels of MAPbI(3) shift toward higher binding energy by 0.25 eV due to electron transfer from MAPbI(3) to MoOx. Its conduction band edge is observed to almost pin to the E-F, indicating a significant enhancement of conductivity. Meanwhile, the energy levels of MoOx shift toward lower binding energy by similar to 0.30 eV, and an interface dipole of 2.13 eV is observed at the interface of MAPbI(3)/MoOx. Most importantly, the chemical reaction taking place at this interface results in unfavorable interface energy level alignment for hole extraction. A potential barrier of similar to 1.36 eV observed for hole transport will impede the hole extraction from MAPbI(3) to MoOx. On the other hand, a potential barrier of similar to 0.14 eV for electron extraction is too small to efficiently suppress electrons extracted from MAPbI(3) to MoOx. Therefore, such an interface is not an ideal choice for hole extraction in organic photovoltaic devices. (C) 2015 AIP Publishing LLC.