The origin of hole injection improvements with MoO₃/Al bilayer electrodes in pentacene thin-film transistors

The electronic structures of pentacene/MoO₃/Al and pentacene/Al were studied using in situ photoemission spectroscopy. The secondary electron cutoffs, highest occupied molecular orbitals (HOMOs) and core level changes were measured upon deposition of the pentacene and MoO₃ to study the electronic structures at the interface. We obtained complete energy level diagrams for each interface, showing that the insertion of the MoO₃ layer between pentacene and Al induces the HOMO level shift of pentacene toward lower binding energies compared to that without MoO₃. This results in reduction of the hole injection barrier, which is responsible for the improvements in electronic device performance.