High efficiency and long lifetime in organic light-emitting diodes using bilayer electron injection structure

A lithium quinolate-based electron injection structure was developed to improve luminance efficiency and lifetime of organic light-emitting diodes (OLEDs). A electron injection material based on Li complex, 8-hydroxyquinolinato lithium (Liq), was introduced as an electron injection material for OLEDs and the efficiency and lifetime of OLEDs were investigated according to the structure of the electron injection layer. A bilayer electron injection structure, a mixed layer of tris(8-hydroxyquinoline) aluminium (Alq₃) and Liq and a Liq layer, showed high efficiency of 11.6 cd/A compared with 9.8 cd/A for lithium fluoride (LiF). In addition, the extrapolated lifetime of OLED with the bilayer electron injection structure was improved by 40% at 1000 cd/m².