Improvement of light extraction efficiency and reduction of driving voltage in organic light emitting diodes using a plasmonic crystal

Abstract

Two-dimensional periodic corrugation was introduced into the surface of metallic cathodes of organic light-emitting diodes (OLEDs) to extract surface plasmon energy, which is trapped in that surface, as free-space photons. The dependence of the improvement factor of the emission efficiency on the modulation depth of the corrugation was systematically investigated. The corrugation was fabricated by using a colloidal lithography technique, which can be easily applied to a wide area. The obtained maximum improvement factor in current efficiency was 1.67 for an OLED with a 40 nm modulation depth, whereas the improvement in power efficiency was 2.35 for an OLED with a 60 nm modulation depth. We attributed the former improvement factor purely to optical effects and the latter to both optical and electrical effects, namely, a reduction of the electrical resistance of the organic layers due to the introduced corrugation.

Nanosinusoidal Surface Zinc Oxide for Optical Out-coupling of Inverted Organic Light-Emitting Diodes

“…Here, a sin. ZnO film with broad quasi-periodicities of a few hundred nanometers from randomly distributed 350 nm SiO 2 nanoparticles and a groove depth of approximately 60 nm is fabricated to effectively enhance the out-coupling efficiency of OLEDs. , The structures of the devices used in this paper are illustrated in Figure . The flat or sin.…”

“…Fabricating nanostructures occasionally requires high temperature, high-cost, or complicated processes and techniques such as electron beam lithography, laser interference lithography, or nanoimprinting with molding and replicating. − To fabricate nanostructures more simply, nanoparticles can be employed with a solution process at low cost. ,, However, additional nanoparticles or extra layers with residues could alter the electrical characteristics, charge balance, and lifetime of an optimized OLED. Furthermore, in the case of inserting insulating nanostructures between the substrate and the bottom electrode, contact between a TFT and an OLED pixel would be unfeasible without an additional nanostructure patterning process. − Additionally, only a few papers have reported on the lifetime of OLEDs having out-coupling nanostructures, , presumably due to the usual adverse effect of locally high current densities or defects on the lifetime of OLEDs depending on the nanostructure’s shape and fabrication methods. − Therefore, an alternative way of easily fabricating nanostructure by utilizing a simple and low-cost nanoparticle solution process to improve the out-coupling efficiency of an inverted OLED without changing the electrical characteristics or deteriorating the lifetime of the device should be developed.…”

Light manipulation in organic light‐emitting devices by integrating micro/nano patterns

“…In case of a periodic micro/nano pattern is introduced, besides the grating period, the amplitude of the grating is an important factor to affect the light extraction efficiency of the OLEDs . The optimal depth for the optical and electrical properties is usually not coincident.…”

Enhanced light extraction efficiency and viewing angle characteristics of microcavity OLEDs by using a diffusion layer

“…The light trapped in the substrate mode that results from the TIR at the interface between the glass substrate (n = 1.5) and air (n = 1.0) was extracted by using an external scattering layer, patterned glass, an array of microlenses, or a textured mesh surface [9][10][11][12][13][14][15][16] . Furthermore, the light trapped in the waveguide mode, which results from the TIR at the interface between the ITO (n = 1.9) and glass substrate (n = 1.5), was extracted by utilizing a randomly distributed nano-sized structure, an internal scattering layer, a periodic photonic crystal, or a layer with a low refractive index [17][18][19][20][21][22][23] . However, to a certain extent, the aforementioned external and internal light extraction technologies are problematic in that they adversely affect the display and are dependent on certain wavelengths and viewing angles, experience the pixel blurring effect, and require an expensive and complicated fabrication process to achieve the desired light extraction 24,25 .…”