Flexible Top-Emitting Organic Light-Emitting Diodes Using Semi-Transparent Multi-Metal Layers

Abstract

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.

Nanocomposite Electron-Transport Layer Incorporated Highly Efficient OLED

“…High-efficiency yellow organic light-emitting diodes (OLEDs) have shown promising potential for the fabrication of solid-state lighting sources, flat panel displays, and lighting applications. − OLEDs have attracted huge attention from academia and industry because of their superior characters such as low power consumption, wide-angle view, flexibility, and long lifetime. − Less fabrication complexity, high efficiency, and long lifetime are major driving forces allowing commercialization of OLEDs into the market. − Therefore, mass-produced OLED television screens, mobile displays, and lighting panels are now enthusiastically available in our daily life. − Since the invention of OLED reported in 1987, noteworthy enhancements have been realized in the performance of high-efficiency and long-lifetime OLEDs due to the prodigious efforts of researchers in the synthesis of effective materials and device architecture engineering. − However, ensuring applications that involve high-efficiency OLEDs compared with typical displays remain challenging in terms of brightness, efficiency, and especially lifetime, thus limiting their commercialization. , Therefore, solution processing of a pinhole-free thin film has drawn much attention for the production of high-efficiency devices having qualities such as large area, complexities, and low-cost processing. , However, solution processing has critical limitations in terms of material processing such as solubility in appropriate solvents, lifetime of guests, air stability, and thin-film uniformity and thickness . To overcome such limitations, thermal evaporation processing provides excellent characteristics allowing multilayered deposition, accurate control of layer thickness, and good thin-film uniformity, which are extremely crucial for a high-performance device. ,, The vacuum deposition encountered numerous issues such as high cost, low throughput, complicated process, and high material consumption. , Hence, solution processing of materials may be an ideal technique to enhance the performance of devices.…”

Semi-transparent polymer light emitting diodes with multiwall carbon nanotubes as cathodes

“…Such a characteristic has great potential in semi‐transparent tablets, screens, active matrix applications, and flexible electronics . Several groups have been working with top‐emitting polymer light emitting diodes (TOLEDs), which use thin metal films such as silver and aluminum as semitransparent cathode , The disadvantage of such approach is exciton quenching at the metal cathode and losses of brightness due to low transmittance in thin layers of metals , this complicates the elaboration of efficient PLEDs with double side emission. The problem of transmittance in the cathode for OLEDs have been partially solved by using transparent conductive oxides, Park et al reported a transparent PLED with double side emission, where the transparent cathode aluminum doped zinc oxide (AZO) was deposited by sputtering but the brightness was less than 100 Cd/m 2 at 30 V .…”