Properties of non-doped organic light-emitting devices based on an ultrathin iridium complex phosphor layer

Abstract

Organic light-emitting devices (OLEDs) were constructed with a structure of indium tin oxide (ITO)/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) (50-x nm)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C²′] iridium (acetylacetonate) [(t-bt)₂Ir(acac)] (d nm)/NPB (x nm)/2,2′,2′′(1,3,5-benzenetriyl)tris-(1-phenyl-1H-benzimidazole) (TPBI) (30 nm)/Mg:Ag (200 nm). A thin blue emission material of NPB was used as a separating layer, and the (t-bt)₂Ir(acac) yellow phosphorescent dye was acted as an ultrathin light-emitting layer. TPBI acted as both hole-blocking and electron-transporting layer. By changing the location (x) and the thickness (d) of the phosphor dye, the variation of device performance were investigated. The results showed that all the devices had a turn-on voltage of 2.8 V. In the case of d=0.2 nm and x=5 nm, the OLED had a maximum luminance of 18367 cd/m² and a maximum power efficiency of 5.3 lm/W. The high performance is attributed to both direct charge carrier trapping of iridium phosphor dye and the thin NPB separation layer, which effectively confines the recombination zone of charge carriers.

Keywords

organic light-emitting devices (OLEDs) / irid- ium complex phosphor dye / ultrathin layer / separation layer

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Higher Education Press and Springer-Verlag Berlin Heidelberg