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

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 °C is inserted between the cathode and PDMS for the subsequent mold removal at 150 °C by melting polystyrene. Current efficiency of 3 cd/A (1.1%) and luminance of 2500 cd/m2 are achieved for green polyfluorene fluorescent emitter. 25 cd/A (8.2%) and 3200 cd/m2 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.

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► The low work function cathode of OLED is made by lamination process.
► External quantum efficiency of 1.1% is achieved for green fluorescent emitter.
► External quantum efficiency of 8.2% is achieved for green phosphorescent emitter.