Efficient Green Phosphorescent Organic Light-Emitting Diodes Depending on Concentration of Lithium Quinolate in Electron Transport Layer

Systematic studies on carrier injection and transport are very important for achieving high efficiency in OLEDs. We demonstrate excellent green phosphorescent organic light-emitting diodes (OLED) with lithium quinolate (Liq) doped in 1,3,5-tris(N-phenylbenzimidazole-2-yl) benzene (TPBi) as the electron transport layer (ETL). The doping concentration of Liq was varied from 0% to 10%. The optimized green phosphorescent OLED with 5% Liq in the ETL showed the best efficiencies, which were maximum luminous efficiency, power efficiency, and quantum efficiency of 65.76 cd/A, 57.39 Im/W, and 20.03%, respectively. Moreover, high triplet energy states of TCTA and TPBi as a triplet exciton-blocking layer (TEBL) played a role in efficient exciton confinement.