Patterning Scheme Based on Photoacid Induced Spectral Changes for Single Layer, Patterned Full Color Light Emitting Diod
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Patterning Scheme Based on Photoacid Induced Spectral Changes for Single Layer, Patterned Full Color Light Emitting Diodes Maria Vasilopoulou1, Giorgos Pistolis2, Athanasios Botsialas3, Nikos Stathopoulos3, Maria Rangoussi3, and Panagiotis Argitis1 1 Institute of Microelectronis, National Center for Scientific Research "DEMOKRITOS", Aghia Paraskevi, Athens, 15310, Greece 2 Institute of Physical Chemistry, National Center for Scientific Research "DEMOKRITOS", Aghia Paraskevi, Athens, 15310, Greece 3 Dep. of Electronics, Technological Education Institute of Piraeus, 250, Thivon str., Athens, 12244, Greece
ABSTRACT Photochemically induced emission tuning (PIET) for the definition of different color emitting areas in a single conducting polymeric layer is demonstrated. The commercially available poly(9-vinylcarbazole) (PVK), well known as a hole transporting layer in OLEDs technology, was used. The three primary colors emitting areas in a single layer of PVK film were defined using a suitable green emitter 1-[4-(dimethylamino)phenyl]-6-phenylhexa-1,3,5,-triene (DMA-DPH) along with the red emitter (4-dimethylamino-4’-nitrostilbene) (DANS). The selected emitters were dispersed in the PVK films in the presence of a photoacid generator (PAG). Various onium salts were tested as photoacid generators in order to select those, which could cause effectively the photoinduced protonation and emission tuning of the probes molecules. Through proton induced bleaching of the red emitter and proton induced spectral shift of the green one, the definition of all three primary colors emitting areas was possible. In this way the unexposed areas of the film remain red, the areas exposed with the intermediate dose become green and the fully exposed areas emit blue color. Intermediate colors and white light can also be obtained.
INTRODUCTION Organic light emitting diodes (OLEDs) are currently under active research due to their applications in flat panel displays and solid state lighting. In the context of this research effort a good number of conducting polymers and small organic molecule based materials with acceptable characteristics have been synthesized [1], and their successful use in device fabrication has been demonstrated in many cases [2]. Solution processing of OLEDs is an alternative fabrication route offering flexibility and low cost. The generation of a full-color image in a display requires the existence of nearby discrete areas, which are capable to emit one of the three primary colors i.e. red, green or blue. Several techniques have appeared for producing the three colors needed in each pixel. In general, the manufacture of a full-color
display involves the formation of multi-layer structures that means, deposition and patterning of different polymeric or small organic molecule based layers one over the other, where each one is capable of emitting one of the three-main colors [3]. Nevertheless, the deposition and patterning of each individual layer involves quite a few processing steps and in addition risks fo
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