Flexible top-emitting organic light-emitting diodes using semi-transparent multi-metal layers

In this paper, the improved device performance of top-emitting organic light-emitting diodes (TEOLEDs) with a thin multi-metal layer stack of nickel/silver/nickel (Ni/Ag/Ni) and aluminum/silver/aluminum (Al/Ag/Al) that were used as the anode and cathode on a flexible substrate is discussed. In particular, Indium-Tin-Oxide (ITO) as an anode electrode has been used recently even though it has some problems for flexible devices. Therefore we suggested that a thin multi-metal layer electrode as a new anode is fabricated instead of ITO anode. It was verified that the ITO-free TEOLEDs showed an enhanced probability of the recombination of the electrons and holes through an improved electron/hole charge balance. We also analyzed the optical and electrical characteristics using the current density, luminance, luminance efficiency, external quantum efficiency (EQE), CIE x, y coordinates, and EL spectra of flexible TEOLED devices were characterized. ITO-free, flexible, green-emitting OLEDs with a low cost and a simple process were demonstrated.