Vacuum-free lamination of low work function cathode for efficient solution-processed organic light-emitting diodes

Abstract

The low work function cathode of blade-coated organic light-emitting diode is transferred from a soft polydimethylsiloxane (PDMS) mold by lamination without vacuum. The cathode is a bilayer of polyethylene glycol (PEG) (< 10 nm) and Al (100 nm). A sacrificial layer of polystyrene with low Mw 1500 and melting point of 120 degrees C is inserted between the cathode and PDMS for the subsequent mold removal at 150 degrees C by melting polystyrene. Current efficiency of 3 cd/A (1.1%) and luminance of 2500 cd/m(2) are achieved for green polyfluorene fluorescent emitter. 25 cd/A (8.2%) and 3200 cd/m(2) are achieved for green phosphorescent tris[2-(p-tolyl) pyridine] iridium(III) (Ir(mppy)(3)) emitter in polymer blend host. The efficiency is about 70% of the devices with thermally evaporated cathode. The turn-on voltage is about 5 V higher. (C) 2011 Elsevier B. V. All rights reserved.