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We describe a synergistic effect of a lifetime-extending light-emitting-layer (LEL) additive and improved electron injection and transport in organic light-emitting diodes (OLEDs). Previously reported di(2-naphthyl)perylene (DNP) serves as the LEL additive capable of extending the operating lifetime of OLEDs by over two orders of magnitude. Using 2-phenyl-9,10-di(2-naphthyl)anthracene (PADN) as an electron-transport layer (ETL) and a separate layer of 4,7-diphenyl-1,10-phenanthroline (BPhen) as an electron-injection layer (EIL) significantly improves electron delivery into the charge recombination zone relative to traditional ETL made of tris(8-quinolinolate)aluminum (Alq). This ETL∣EIL combination not only results in approximately seven times lower electric field in the ETL and, thus, lower drive voltage and higher efficiency devices, but can also increase device lifetime substantially. In a representative device containing a red-emitting LEL dopant Commission Internationale de l’Eclairage 1931 2° color chromaticity coordinates (CIEx,y) of 0.65, 0.35, the external quantum efficiency, electroluminescence yield, drive voltage, and operating half-life (t50) can reach 5.8%, 6.5cd∕A, 4.5V, and ∼1000000h, respectively, all at 20mA∕cm2 current density.
Jarikov et al. (Thu,) studied this question.