Organic light-emitting diodes with structured cathode

Abstract

Organic light-emitting diode (OLED) devices were fabricated with a structured polymer-cathode interface. The devices have a layered structure indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/poly(2-methoxy-5-[(2′-ethylhexyl)oxy]-p-phenylenevinylene)/Al. The light-emitting polymer layers were patterned via a stamp imprinting process, followed by vapor deposition of the cathode. Devices employing the structured cathode showed improved electron injection and increased brightness when compared to conventional flat cathode devices. Electrostatic modeling of the structured cathode geometry revealed localized increase in electric field leading to enhanced electron tunneling through the polymer-cathode interface. Thus, improved OLED performance was demonstrated from cathode microstructuring.

Analysis of pinning effect at the Alq3/metal interface in organic light emitting diodes

“…4 Lots of work are in literature about the improvement of the cathode efficiency. [5][6][7][8][9][10][11][12][13] Several metals have been employed in OLEDs in order to increase the electron injection such as magnesium, calcium, aluminum, silver, antimony, and ytterbium; 5 carbon nanotubes 6 have shown an increasing of the electric field because of their geometry; transparent electrode 7 have been realized by using compounds of molybdenum obtaining low cathode sheet resistance and good device efficiency. Moreover, the usage of particular structures has been widely employed: microstructured cathode-semiconductor interfaces have been realized by the means of microimprinting techniques; 8 the adoption of LiF, C60, and CsF (Refs.…”

Enhanced luminance of organic light-emitting diodes with metal nanoparticle electron injection layer

“…There was no apparent change of the emission spectra after Mg-Ni nanoparticles are implemented. Similarly to what we demonstrated in our previous work [13], the improved performance of the OLED devices can to be attributed to enhanced electron tunnel injection brought about by local field enhancement resulting from the small geometry of Mg-Ni nanoparticles.…”

“…In our previous work [13], imprinting microlithography technique was used to realize a structured cathode. The electric field at the cathode-organic interface was increased due to the resulting cathode geometry, which altered the otherwise flat equipotential planes near the cathode.…”

Enhanced luminance of MEH-PPV based PLEDs using single walled carbon nanotube composite as an electron transporting layer

“…This is due to the fact that SWCNTs have high mobility for electrons and thus help in balancing the carrier concentration of electrons and holes in the emissive layer, resulting in enhanced emission from the device. Besides this, it was shown by Liu et al [22] that the introduction of SWCNTs at the cathode-polymer interface enhances the local electric field. In terms of the Fowler-Nordheim tunneling theory [23], the increase in local electric field implies the increase in electron injection from the cathode.…”