Dipole Formation at the MoO₃/Conjugated Polymer Interface

MoO₃ is known as high work function (WF) transparent metal oxides. It is used as anode buffer layer in organic based solar cells because of its capability to extract electrons and inject holes from the active layer due to its high WF. Here a broad range of techniques is used to determine the energy levels of the bulk heterojunction (BHJ) and MoO₃ to determine that the minimum deposition thickness to achieve a closed layer is 1 nm due to penetration of the evaporated MoO₃ into the BHJ. The investigation shows that upon evaporation of the MoO₃, a strong dipole is formed at the extended interface between the active layer and the MoO₃ and that the strength of the dipole increases with increasing thickness of the MoO₃ layer and saturates at 2.2 eV at a thickness around 3 nm.