Three-Color Passive-Matrix Pixels Using Dye-Diffusion-Patterned Tri-Layer Polymer-Based LED
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Three-Color Passive-Matrix Pixels Using Dye-Diffusion-Patterned Tri-Layer Polymer-Based LED Ke Long, Florian Pschenitzka and J. C. Sturm Center for Photonics and Optoelectronic Materials (POEM), Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 ABSTRACT Dry dye-printing and solvent-enhanced dye diffusion were used to locally dope a previously spin-coated poly(9-vinylcarbazole) (PVK) polymer film with different dyes to fabricate side-by-side RGB OLED pixels. To reduce reverse leakage current and raise efficiency, a blanket tris-8-hydroxyquinoline aluminum (Alq) electron transport layer (ETL) was deposited over the polymer layer after the dye diffusion step, along with a 2,9-dimethyl-4,7diphenyl-1,10-phenanthroline (BCP) hole/exciton blocking layer between the Alq and the PVK to ensure all light emission occurred from the doped polymer and not from the Alq. Devices with this tri-layer structure have an extremely low reverse leakage current (rectification ratio of 106 at +/- 10V) and a higher external quantum efficiency (~1%) than single layer devices. A three-color passive-matrix test array with 300µm x 1mm RGB subpixels was demonstrated with this structure. INTRODUCTION Organic light-emitting devices (OLEDs) are of great interest for flat panel display applications. Passive-matrix is a preferable driving scheme because of its simplicity and low fabrication cost. Polymers are attractive emission materials for OLED displays because they can be deposited by low-cost and high-throughput methods such as spin-coating. However, spincoating creates blanket layers. For efficient full-color displays, pixels emitting red, green and blue (RGB) colors should be fabricated side by side on the same substrate. Therefore patterning the polymer layer to achieve RGB colors is critical. The emission colors of polymers can be controlled by adding a small amount of fluorescent dyes into the polymer film (less than 1% by weight) [1]. There are several methods to achieve full color based on this principle, for example ink-jet printing of a dye solution on a previously spin-coated polymer film [2], photobleaching of a dye [3], patterned dye transfer by local heating [4], and thermal transfer through a mask [5]. More recently, we have focused on a local dye transfer process, with two steps, where the dye is first printed onto the device polymer surface using a patterned soft printing plate, followed by diffusion into the polymer film [6]. To lower the temperature required to uniformly diffuse the dye throughout the device polymer from over 100°C to room temperature, a solvent-vapor annealing step has been adopted [7]. The goal of this paper is to extend this transfer process to create RGB devices suitable for a full-color passive matrix. Conventionally polymer-based OLEDs often consist of only a single polymer layer, sandwiched between anode and cathode. The single-layer dye-doped polymer LED has high leakage current under reverse bias, which is not compatible with passive-matrices because of the cross-ta
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