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.
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.
The search for stable electron transporters and hole injectors has become particularly intense over the last 12 months as OLED manufacturers are poised to start production of OLED panels. We report here a proprietary electron transporter (E246), which reduces the operating voltage, increases the efficiency and the lifetime of OLEDs made of fluorescent or phosphorescent systems when compared with Alq3 as an electron transporter. We also report a novel proprietary hole injector (buffer, E9363) which also reduces the operating voltage, increases the efficiency and doubles the lifetime compared to CuPC. E246 has been validated on both ULVAC and Tokki vacuum evaporators. These two materials are now available commercially for display manufacturers.
Charge transport and charge balance are critical for achieving high performance and long life time .Thus, electrical, electronic and thermal properties of all the materials have to be optimised There is continuing demand for electron transporters with good hole blocking property and electron injectors for use as individual layers or as admixtures. Most of the commercially employed electron transporters are either based on Al, Zr or Sc or electron deficient compounds based on oxadiazole(s), pyridine(s), phenanthroline(s) or pyrimidine(s). Lithium complexes are used as electron injectors, usually up to 2 nm. At thicknesses above 2 nm, they act as insulators, thus reducing the performance of OLED's. Therefore, they cannot be used as electron transporters where the typical thickness is 20 nm. This paper reports our discovery of unique and novel lithium complex with ligand 2-(2hydroxylphenyl)-5-methylbenzoxazole which behaves like an electron transporter rather than an injector. Several complexes of Li, Be, Zn,Al and Zr were made with several hydroxylphenyl benzoxazole(s) and hydroxyphenyl benzothiazole(s)and their properties narrated. Particular emphasis is given to the unusual behaviour of the Lithium compound.
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