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.