The preparation of multilayer structures by solution filmcoating techniques is difficult because of the solubility of the bottom layer onto which the top layer will be cast. The utilization of precursor polymers and their thermal conversion into an insoluble film well established for instance for poly(p-phenylenevinylene) (PPV) alleviates this problem. A different approach is to convert soluble monomers or pre-polymers containing polymerizable moieties either as side groups or in the main chain into an insoluble material using photo-crosslinking reactions. However, such materials often require additional thermal treatment to obtain an insoluble layer, leading to a drop in performance. Here, we report the properties of a series of photo-crosslinkable acrylate hole transport polymers based upon copolymerization of substituted bis(diarylarmino)-biphenyl acrylate monomers and cinnamate acrylate monomers, and their use in OLEDs, using AlQ3 as emitting material. Only few seconds of UV exposure using a commercial mask aligner under ambient conditions are necessary to obtain an insoluble hole-transport layer with stable performance. Lifetimes under constant current operation of devices using these polymers have been measured and compared to their small molecules evaporated equivalents. Fully spin-coated EL devices have been fabricated using a blend of polystyrene and AlQ3.
Benoit Domercq, Richard D. Hreha, Nathalie Larribeau, Joshua N. Haddock, Christopher Schultz, Yadong Zhang, Seth R. Marder, Bernard Kippelen, "Patternable Polymers as Hole Transport Materials for Organic Light-Emitting Diodes" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP18), 2002, pp 428 - 428, https://doi.org/10.2352/ISSN.2169-4451.2002.18.1.art00001_2