ITO-free large-area top-emission organic light-emitting diode by blade coating

• We fabricate ITO-free large-area top-emitting OLEDs via blade coating process.
• The light-emission uniformity within 10% variation in the area of 2 cm by 2.5 cm.
• The large-area devices show comparable current efficiency as small area devices.
• CsF and n-doped electron transport layer are applied to improve electron injection.

Large-area top-emitting organic light-emitting diodes (TEOLEDs) with multi-layer structure are successfully demonstrated using the solution-processable blade coating on ITO-free substrate. The semitransparent cathode of TEOLED is composed of lithium fluoride (LiF), aluminum (Al) and silver (Ag). The composition of 3 nm Al and 10 nm Ag has a transmittance of 56% and a sheet resistance of 11 Ω/□. It is applied to the green phosphorescence device with an emissive area of 2 cm by 2.5 cm. The maximum current efficiency is 25.2 cd/A with high light-emission uniformity within 10% variation. The large-area TEOLEDs show comparable current efficiency as the small-area devices with an emissive area of 2 mm by 2 mm (having the same device structure) and better efficiency than traditional large-area bottom-emitting devices. Cesium fluoride (CsF) and n-doped electron transport layer are applied to improve electron injection. At 6 V, the luminance is raised from 141 cd/m2 to 502 cd/m2 and 304 cd/m2, respectively. In n-doped device, a simple Al/Ag cathode is used without LiF.