Improving light extraction for OLED devices will be pivotal for their acceptance into the marketplace. Incorporating
nanostructures within the high refractive index regions of the OLED multi-layer stack results in an over two-fold
improvement in light extraction efficiency. Such nanostructures were made using roll-to-roll fabrication processes. We
will also discuss the performance characteristics of the nanostructures on color-angularity and blurring of high-resolution
Laser Induced Thermal Imaging (LITI) allows for high-resolution patterning of a variety of materials that often cannot be patterned efficiently by other conventional techniques such as photolithography. Application of LITI towards patterning vacuum-coated OLED materials is particularly attractive because of high LITI patterning resolution and accuracy and good compatibility of vacuum-coated OLED materials. However, LITI may induce thermal transfer defects within OLED materials. We are developing methods to address these potential thermal defects while maintaining patterning quality, device operation efficiency, voltage, and lifetime. Recent results regarding optimization of LITI for patterning vacuum-coated OLEDs will be discussed.
Laser Induced Thermal Imaging (LITI) is a high resolution, digital patterning technique developed at 3M for use in a number of applications including the patterning of LCD color filters and OLED emitters. The LITI process is suited for the manufacture of flat panel displays, where both high resolution and absolute placement accuracy are required. In this paper, we present the capabilities of LITI, the basic design of a LITI laser imager, the construction of a LITI donor sheet, and the process by which OLED emitters may be patterned. An OLED device fabricated with the LITI process is described.
We have fabricated saturated red, orange, yellow and green OLEDs, utilizing phosphorescent dopants. Using phosphorescence based emitters we have eliminated the inherent 25% upper limit on emission observed for traditional fluorescence based systems. The quantum efficiencies of these devices are quite good, with measured external efficiencies > 15% and > 40 lum/W (green) in the best devices. The phosphorescent dopants in these devices are heavy metal containing molecules (i.e. Pt, and Ir), prepared as both metalloporphyrins and organometallic complexes. The high level of spin orbit coupling in these metal complexes gives efficient emission from triplet states. In addition to emission from the heavy metal dopant, it is possible to transfer the exciton energy to a fluorescent dye, by Forster energy transfer. The heavy metal dopant in this case acts as a sensitizer, utilizing both singlet and triplet excitons to efficiently pump a fluorescent dye. We discuss the important parameters in designing electrophosphorescent OLEDs as well as their strengths and limitations. Accelerated aging studies, on packaged devices, have shown that phosphorescence based OLEDs can have very long device lifetimes.