2,792 research outputs found
A solution processed flexible nanocomposite electrode with efficient light extraction for organic light emitting diodes.
Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m(2) with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost
High-Contrast OLEDs with High-Efficiency
Peer reviewed: YesNRC publication: Ye
Flexible distributed Bragg reflectors as optical outcouplers for OLEDs based on a polymeric anode
Top-emitting OLEDs (TOLEDs) represent a promising technology for the development of next-generation flexible and rollable displays, thanks to their improved light outcoupling and their compatibility with opaque substrates. Metal thin films are the most used electrodes for the manufacturing of TOLEDs, but they show poor resistance to mechanical deformation, which compromises the long-term durability of flexible devices. This paper reports the exploitation of a dielectric mirror (DBR) based on seven pairs of TiO2 and SiO2 combined with a polymeric electrode as an alternative to the bottom metal electrode in flexible TOLEDs. The DBR showed a maximum reflectivity of 99.9% at about 550 nm, and a stop-band width of about 200 nm. The reflectivity remained unchanged after bending and treatment with water and solvents. Green TOLED devices were fabricated on top of DBRs, and demonstrated good stability in terms of electro-optical and colorimetric characteristics, according to varying viewing angles. These results demonstrate that the combination of the flexible DBR with the polymeric anode is an interesting strategy for improving the durability of flexible TOLEDs for display applications, implemented on different kinds of free-standing ultra-thin substrates
Enhanced light emission from top-emitting organic light-emitting diodes by optimizing surface plasmon polariton losses
We demonstrate enhanced light extraction for monochrome top-emitting organic
light-emitting diodes (OLEDs). The enhancement by a factor of 1.2 compared to a
reference sample is caused by the use of a hole transport layer (HTL) material
possessing a low refractive index (1.52). The low refractive index reduces the
in-plane wave vector of the surface plasmon polariton (SPP) excited at the
interface between the bottom opaque metallic electrode (anode) and the HTL. The
shift of the SPP dispersion relation decreases the power dissipated into lost
evanescent excitations and thus increases the outcoupling efficiency, although
the SPP remains constant in intensity. The proposed method is suitable for
emitter materials owning isotropic orientation of the transition dipole moments
as well as anisotropic, preferentially horizontal orientation, resulting in
comparable enhancement factors. Furthermore, for sufficiently low refractive
indices of the HTL material, the SPP can be modeled as a propagating plane wave
within other organic materials in the optical microcavity. Thus, by applying
further extraction methods, such as micro lenses or Bragg gratings, it would
become feasible to obtain even higher enhancements of the light extraction.Comment: 11 pages, 6 figures, will be submitted to PR
Emission Characteristics of Organic Light-Emitting Diodes and Organic Thin-Films with Planar and Corrugated Structures
In this paper, we review the emission characteristics from organic light-emitting diodes (OLEDs) and organic molecular thin films with planar and corrugated structures. In a planar thin film structure, light emission from OLEDs was strongly influenced by the interference effect. With suitable design of microcavity structure and layer thicknesses adjustment, optical characteristics can be engineered to achieve high optical intensity, suitable emission wavelength, and broad viewing angles. To increase the extraction efficiency from OLEDs and organic thin-films, corrugated structure with micro- and nano-scale were applied. Microstructures can effectively redirects the waveguiding light in the substrate outside the device. For nanostructures, it is also possible to couple out the organic and plasmonic modes, not only the substrate mode
Transparent electrode of nanoscale metal film for optoelectronic devices
This paper reviews the principles, impediments, and recent progress in the development of ultrathin flexible Ag electrodes for use in flexible optoelectronic devices. Thin Ag- based electrodes are promising candidates for next- generation flexible transparent electrodes. Thin Ag- based electrodes that have a microcavity structure show the best device performance, but have relatively low optical transmittance (OT) due to reflection and absorption of photons by the thin Ag; this trait causes problems such as spectral narrowing and change of emission color with viewing angle in white organic light- emitting diodes. Thinning the Ag electrode to < - 10 nm thickness (ultrathin Ag) is an approach to overcome these problems. This ultrathin Ag electrode has a high OT, while providing comparable sheet resistance similar to indium tin oxide. As the OT of the electrode increases, the cavity is weakened, so the spectral width of the emission and the angular color stability are increased. (C) 2015 Society of Photo- Optical Instrumentation Engineers (SPIE)1162Ysciescopu
Photon Generation and Dissipation in Organic Light-Emitting Diodes
By using phosphorescent and thermally activated delayed fluorescence emitters, the internal quantum efficiency of organic light-emitting diodes (OLEDs) can now reach 100%. However, a major fraction of generated photons is trapped inside the device, because of the intrinsic multi-layer device structure and the mismatch of refractive indices. This thesis comprises different approaches for the efficiency enhancement of planar OLEDs. In particular, outcoupling strategies to extract trapped photons to obtain highly efficient OLEDs are investigated
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