Conor F. Madigan

Improvement of output coupling efficiency of organic light-emitting diodes by backside substrate modification

The emission intensity of an organic light-emitting diode at normal viewing angle and the total external emission efficiency have been increased by factors of 9.6 and 3.0, respectively, by applying spherically shaped patterns to the back of the device substrate. The technique captures light previously lost to waveguiding in the substrate and, with proper choice of substrate, light previously lost to waveguiding in the organic/anode layers. A method of applying the technique using laminated films and an optical model for evaluating coupling efficiency are also presented.

Matching architecture to application via configurable processors: a case study with boolean satisfiability problem

Boolean Satisfiability (SAT) is a classical NP-complete problem with both theoretical and practical interests. This paper presents our work in developing an application-specific processor for SAT based on a commercial configurable processor core. We customize the processor configuration and design new instruction extensions based on the data structure and atomic operations used in SAT. The customized processor has achieved around 24 /spl times/ speedup at a very low hardware cost. The small size of the processor makes it possible to integrate multiple processors and other customized logic into a single chip for an application-specific multiprocessor solution for SAT. Our work shows the strength of application-specific processing in accelerating applications with complex control and dynamic data structures - an area that has traditionally not been targeted by application-specific processing. It also demonstrates that configurable processor cores can be used to cut the development time and cost for designing and building such application-specific processors.

Improved external coupling efficiency in organic light-emitting devices on high-index substrates

High-index-of-refraction substrates are shown theoretically and experimentally to increase the external coupling efficiency of organic light-emitting devices (OLEDs) by using a quantum mechanical microcavity model. This increase is due to the elimination of those modes waveguided in the ITO/organic layer. Bi-layer OLEDs were fabricated on standard soda lime glass and high-index glass substrates, and their far-field intensity pattern was measured. Among the devices optimized for external efficiency, those on shaped high-index substrates exhibited a 53% improvement in external quantum efficiency over the devices on shaped standard glass substrates, and an increase by a factor of 2-3 times over those on planar glass substrates. This principle is applicable to any backside patterning technique in conjunction with other OLED structural improvements.

Experiment and Modeling of Conversion of Substrate-Waveguided Modes to Surface-Emitted Light by Substrate Patterning

To predict the optical power that could be harvested from light emission that is waveguided in the substrate of organic light emitting devices (OLEDs), a quantitative quantum mechanical model of the light emitted into the waveguided modes has been developed. The model was used to compute the exact distribution of energy in external, substrate and ITO/organic modes as a function of the distance of the emission zone from the cathode. The results are compared to the classical ray optics model and to experiments in two-layer OLED devices. Classical ray optics is found to substantially over-predict the light in waveguided modes. INTRODUCTION OLEDs have received enormous interest because of their promise for cheaper and more efficient flat panel displays. A large amount of light is trapped in the substrate due to total internal reflection; therefore, substrate patterning can be used to increase external coupling efficiency [1-3]. The exact distribution of optical energy in all of the waveguide modes has not been calculated previously, except for by classical ray optics. The goal of this paper is to develop such a quantitatively accurate model of such waveguided light and verify it with experiments. The radiative modes can be classified into external, substrate and ITO/organic modes (Figure 1a). External modes are those with angle to the surface normal in the organic layer less than the critical angle between air and Alq3, θc1 = sin nair/nalq; substrate modes are those with angle between θc1 and the critical angle between glass and Alq3, θc2 = sin nglass/nalq; and

Lateral Dye Distribution With Ink-Jet Dye Doping of Polymer Organic Light Emitting Diodes

In this work we investigate the lateral dye distribution resulting from the dye doping of a thin polymer film by ink-jet printing (UIP) for the integration of color organic light emitting diodes (OLEDs). The dye is found to segregate into distinct outer rings following rapid droplet evaporation, while slower evaporation rates are found to significantly reduce (or eliminate) this effect. The dye segregation phenomena are found to depend critically on the mechanisms of droplet evaporation. Good dye uniformity was obtained using a low vapor pressure solvent, and integrated, 250 micron red, green, and blue polymer organic light emitting diodes (OLEDs) were fabricated with this technique. These devices had good color uniformity over most of the device area and similar electrical properties to comparable spin-coated devices without UP.