Electron Transporters Based on Lithium Complexes: Transition from Electron Injecting to Electron Transporting Characteristics

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-(2-hydroxylphenyl)-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.