High-Brightness and Low-Voltage Light-Emitting Devices Based on Trischelated Ruthenium(II) and Tris(2,2‘-bipyridine)osmium(II) Emitter Layers and Low Melting Point Alloy Cathode Contacts

Solid-state light-emitting devices (LEDs) were fabricated based on an amorphous film of Ru(bpy) 3 (ClO 4 ) 2 (bpy = 2,2‘-bipyridine) about 100 nm thick on indium−tin oxide (ITO) with printed low melting point alloys, such as Ga:In, Ga:Sn, and Bi:In:Pb:Sn, as cathodic contacts. A device with the structure of ITO (≤10 Ω/square)/Ru(bpy) 3 (ClO 4 ) 2 /Ga:Sn produces a bright red emission (3500 cd/m 2 at 4.0 V) centered at 660 nm. This new method of making contacts significantly simplifies the fabrication of an electroluminescence cell and has potential application in the production of LEDs by inkjet or microcontact printing. LEDs based on C 12 −Ru(bpy) 3 (ClO 4 ) 2, Ru(phenanthroline) 3 (ClO 4 ) 2, and Os(bpy) 3 (PF 6 ) 2 were also studied. Low melting point alloy contacts were also used with cells based on tris(8-hydroxyquinoline)aluminum.