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A set of novel lithium Schiff base cluster compounds has been synthesised and characterised for the first time and tested as electron injectors in OLED devices. Their electrical, electronic, thermal and optical properties have been investigated and compared with the industry standards LiF and lithium quinolinolate (LiQ). Amongst the compounds tested, lithium 2-((o-tolylimino)methyl) phenolate was found to enhance the efficiency of OLEDs by 69% compared to LiF and 15% compared to LiQ. The same electron injector was found to extend the lifetimes of OLEDs by six-fold compared to LiF and 4.3-fold compared to LiQ respectively. The crystal structure of the parent compound, lithium 2-((phenylamino)methyl)phenolate reveals that the compound is tetrameric in contrast to hexameric LiQ. Substituting the methyl group with fluorine causes a remarkable depression of the HOMO and LUMO levels by up to 1.2 eV. Analysis of current density vs. voltage characteristics of single-layer devices for Li-Al/electron injector/Li-Al and Al/electron injector/Al reveals that both sets of devices are operating as electron-only devices indicating that the formation of free lithium is the cause of enhanced electron injection, but either the energetic aluminium atoms (as proposed previously by other workers) or energetic lithium complexes on an aluminium surface (as we have demonstrated in this paper) are all that is required for efficient electron injection.

Two new phases of zirconium tetrakis(8-hydroxyquinolinolate) (Zrq 4) have been synthesised and characterised by single crystal X-ray diffraction. Their electrical, electronic, optical and thermal properties have been studied. Their electron transporting characteristics have been investigated in organic light emitting devices where the two phases show remarkable differences in performance. One of the forms (designated a-Zrq 4) gives significantly lower operating voltage, higher efficiencies and longer lifetime than the other (designated b-Zrq 4) in organic light emitting devices.

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There is a continuing demand for the reduction in power consumption, operating voltage and lengthening the lifetime of OLED's. Charge transport (hole and electron) materials (pure or doped) are an integral part of any OLED. It has been reported that nearly 60% of the total electric power is lost through the charge transport layers, nearly 36% through etl and 5.7% through eil and the remainder through, hil, htl and hbl. The life time is also critically dependent on the nature of the charge transporters employed. Thus, there is an urgent need for electron transporters with high mobility and stability. We present and demonstrate here some strategies as to the selection of appropriate materials for efficient electron transport and injection resulting in lower operating voltage, higher efficiencies and longer life‐time.