Optimization of carrier mobility in luminescence layers based on europium β-diketonates in hybrid light-emitting structures

The hole conductivity in films of three compounds, complexes based on europium β-diketonates, deposited by vacuum evaporation is studied by the time-of-flight technique. It is shown that no carrier photogeneration is observed in films under pulsed excitation with 337 nm light. The introduction of pentacene-based photogeneration layers into the samples made it possible to observe transient-current curves. It was found that a dispersive component of the transient current, associated with hole transport, is observed in a complex of europium with an auxiliary ligand based on bathophenanthroline. These data were used to determine the hole mobility. No dispersive component of the transient current was observed in complexes with an auxiliary ligand based on phenanthroline. A conclusion is made that the latter is due to the low mobility in compounds of this kind. This is attributed to a decrease in the degree of conjugation of the aromatic system, which occurs on passing from bathophenanthroline to phenanthroline.