Sequestration of electroactive materials in a high Tg, insulating polymer matrix for optoelectronic applications.: Part 1.: Light emitting diode devices

The use of a high T-g, insulating polymer to sequester low molecular weight electroactive materials at high addition levels for utility in LED devices has been demonstrated. The threshold for effective light emission appears to be in the range of 15 wt% electroactive compounds in agreement with the percolation theory of deGennes. The high T-g polymer allows for suppression or elimination of the undesired crystallization of the electroactive species and yields a significant increase in the T-g of the light emitting layer (also required). Additionally this approach offers the potential for easier (and lower cost) fabrication routes not generally employed for low molecular weight electroactive materials (e.g. spin coating, inkjet printing, roll-to-roll printing). The improved mechanical properties of the light emitting layer with high molecular weight polymer addition should allow for improved performance/durability in flexible displays. The simple blend approach should be an attractive alternative to other more common methods reported in the literature employing covalent bonding of electroactive species to polymeric backbones to achieve the same results. This approach also allows for multiple addition of dopants (e.g. laser dyes), hole transport materials and electron transport materials in a single light emitting layer. While these results demonstrate the concept, optimization was not conducted and significant improvements would be expected with proper adjustment of the many variables possible with this approach. (c) 2006 Elsevier Ltd. All rights reserved.