ITO-free, efficient, and inverted phosphorescent organic light-emitting diodes using a WO3/Ag/WO3 multilayer electrode

We present an indium tin oxide (ITO)-free, bottom-emission inverted phosphorescent organic light-emitting diode (PHOLED) with a maximum luminance of 280,000 cd/m(2) at 8 V, total maximum current efficiency of 81.4 cd/A, and external quantum efficiency of 22.4%. The inverted OLED structure is composed of glass/WO3 (30 nm)/Ag (15 nm)/WO3 (5 nm)/BPhen:15wt% CS2CO3 (5 nm)/BPhen (30 nm)/CBP:8wt% Ir(ppy)(3) (10 nm)/TAPC (50 nm)/WO3 (5 nm)/Ag (150 nm) multilayers. In this device structure, the WO3/Ag/WO3 (WAW) multilayer serving as a transparent cathode demonstrates a low sheet resistance (3.5 Omega/sq) and high optical transmittance (approximately 80%) in a visible light range of 400 -600 nm; this multilayer was prepared by thermal evaporation to form a relatively smooth morphology of the conductive thin film on the glass substrate. In addition, an electron-only WAW device was subjected to electrical characterization, and the results revealed that this device exhibited a more efficient electron injection property at the WAW/BPhen:CS2CO3 interface than the contact electrode of a standard ITO-based device. (C) 2016 Elsevier B.V. All rights reserved.