Organic light-emitting diodes (OLEDs) have emerged as a potential candidate for new flat panel display due to their advantages such as low driving voltage, high brightness and luminous efficiency. Since tris(8-hydroxyquinolinato)aluminum (Alq₃)-based double layer thin-film device was prepared, much progress has been made in new electroluminescence (EL) materials which were designed and synthesized by researchers. Organic metal complexes based on 8-hydroxyquinoline and its derivatives are widely used due to simple synthesis, high luminance and efficiency as well as superior film morphology. This paper sketches the advantages, construction and working mechanism of OLEDs and stresses the research progress in small molecular organic EL materials based on 8-hydroxyquinoline and its derivatives as ligands. This article is written basically from the molecular design point of view and aims at the significant developments in metal organic complexes based on 8-hydroxyquinoline and its derivatives that have been designed and synthesized intentionally for OLEDs. Firstly, organic metal complexes based on 8-hydroxyquinoline as single ligand show favourable characteristics such as excellent electron-transport capability, high brightness and employment as host materials. Secondly, the EL colors could be tuned by modification of substituents at phenoxide or pyridine ring. Thirdly, the usage of mixed ligand can increase glass transition temperature and decorate morphology of film then result in high efficiency and stability. In the end, the current status, existing issues and prospects in this field are also discussed. Contents
1 Introduction
2 Structure and working mechanism of OLEDs
2.1 Structure of OLEDs
2.2 Working mechanism of OLEDs
3 Application of 8-hydroxyquinoline organic metal complexes in OLED
3.1 8-Hydroxyquinoline as single ligand
3.2 Derivatives of 8-hydroxyquinoline as ligands
3.3 Complexes of mixed-ligands
4 Conclusion and outlook