Michael Buechel

Ink-jet printing of polymer light-emitting devices

Spin coating is a suitable technique for the fabrication of monochrome light-emitting polymer devices. For color displays, however, it is not the optimal solution when different polymers are applied. In principle, there are several technologies available for patterning light-emitting polymers. In this paper we discuss the advantages of drop-on-demand ink-jet printing over other printing methods. Special attention is given to some fundamental aspects of the printing process, such as drop formation and pixel filling. Examples of both monochrome and full color ink-jet printed passive matrix displays will be discussed.

21.1: Ink Jet Printing of Passive‐Matrix Polymer Light Emitting Displays

The requirement and characteristics for red, green and blue (RGB) electroluminescent polymers[1,2] suitable for fabricating monochrome and full-color passive-matrix polymer display[3] will be discussed. The controlled deposition of the light-emitting polymers is accomplished through the use of high-resolution ink jet printing[4,5], where the materials are first tested in devices prepared using spincoating techniques. The specifications for polymer materials, as well as the display design which must be taken into account to make a high-resolution passive-matrix display with low power consumption are presented.

Technology and materials for full-color polymer light-emitting displays

The status of the development of full-color polymer light emitting diodes will be presented. The focus of current materials research is on state-of-the-art red, green, and blue light-emitting polymers (LEP) with high efficiency, optimum color points, low driving voltages and long lifetimes in devices. A general overview of the progress of red, green and blue LEP lifetimes and efficiencies will be given and compared to requirements for both full-color passive and active matrix-displays for mobile display applications. Further, the status of ink-jet printing of LEPs for the industrialization of full-color displays will be discussed, and a comparison of the performance of spin coated and inkjet printed devices will be presented. In addition, two material-related topics studied recently will be discussed; namely, the lifetime of blue light-emitting devices correlated to processing, anodes, cathodes and the blue polymers themselves, and second, the consequences of pulsed-driving schemes on efficiency and lifetime.

Status of red, green and blue light emitting polymers for passive matrix displays

An overview of the requirements for full color passive matrix displays and their implications for the light emitting materials will be presented. Using the performance of light emitting polymers tested in Philips devices the status of the light emitting polymers is reviewed. It will be shown that the performance of light emitting polymers is at the edge of being acceptable for practical applications. Red and green light emitting polymers can already be used for certain monochrome applications. However, for the high-resolution displays used in mobile telecom applications the efficacy for red and the lifetime for green are still somewhat low. Optimization routes for further improvement in terms of efficacies and lifetimes for red and green are identified. The peformance of blue light emitting polymers has rapidly improved over the last year, but the lifetime is still too short for full color applications. Improvement routes for the blue light emitting polymers and its device structure are outlined.