Improved performance of organic light-emitting diodes (OLEDs) was achieved by implementing a carbon nanotube (CNT) layer at the cathode-organic interface, spin coated between the organic layer and the cathode. The small geometry of CNTs could enable the enhancement of the electric field around them, thus increasing electron injection efficiency from the cathode to the organic layer. In addition, as measured from the x-ray absorption and emission spectroscopy, incorporation of CNT could reduce the lowest unoccupied molecular orbital of the organic material at the cathode-organic interface, thus effectively decreasing the barrier for electron injection. Increased electron injection and luminance characteristics were demonstrated for both polymer and small molecule based OLED devices.

Improvement of the performance of organic lightemitting diodes (OLEDs) was achieved by implementing Magnesium-Nickel nanoparticles at the cathode-organic interface using pulsed laser deposition technique. The small geometry of Mg-Ni nanoparticles acts to enhance the localized electric field around them, thus increasing electron injection through tunneling, from the cathode to the organic layer. Improved current and luminance characteristics were demonstrated for both small molecule and polymer-based OLEDs when the nanoparticle layer was incorporated.PACS 68.35.bd · 78.60.Fi · 78.66.Qn · 85.60.Jb

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.

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Numerical analysis of the electrical effects accompanying nanocolumn patterning at the cathode-organic interface in an injection-limited, single-layer organic light-emitting diode (SLOLED) is conducted. We introduce a carrier-decoupled framework based on the Scott-Malliaras current injection mechanism in the double-sided, injection-limited current regime to simplify the multi-dimensional semiconductor equations in order to analyze the device function in the presence of a periodic nanocolumn array. A semi-analytical treatment is developed to solve the drift-diffusion equations. A common problem in SLOLEDs is unbalanced carrier currents arising from asymmetric injection and transport characteristics. The numerical results for the cathode nanopatterned device predict increased current injection with strongly asymmetrical current enhancement, which is shown to promote carrier injection parity in electron-deficient, single-layer devices by preferentially augmenting cathode-side injection current. Finally, the recombination current enhancement is attained and is shown to be increased by a factor of 8.52 and 3.00 when comparing the nanopatterned SLOLED device with planar devices of thicknesses equal to the unpatterned thickness and nanoimprint-thickness-reduced devices, respectively.