Full-color OLEDs integrated by dry dye printing

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 red, green, and blue (RGB) organic light-emitting device pixels. The fabrication details and the resolution and stability of this patterning technique are discussed. The technique was then used to make combined polymer/ small-molecule devices, in which the printability of polymer for color integration was combined with the superior transport properties and thin-layer capabilities of small molecules for high efficiency and low leakage current. To reduce reverse leakage current and raise efficiency, a blanket tris-8-hydroxyquinoline aluminum (Alq₃) electron transport layer was deposited on top of the polymer layer after the dye diffusion step, along with a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline hole/exciton blocking layer between the Alq₃ and the PVK to ensure that all light emission occurred from the doped polymer and not from the Alq₃. Devices with this hybrid doped polymer/small molecule structure have an extremely low reverse leakage current (with a rectification ratio of 10⁶ at ±10 V). The electroluminescence efficiency of the devices was optimized by varying the dye concentration of the printing plate. A three-color passive-matrix test array with 300 μm × 1 mm RGB subpixels was demonstrated with this structure.