Solid-State Light-Emitting Devices Based on the Tris-Chelated Ruthenium(II) Complex. 4. High-Efficiency Light-Emitting Devices Based on Derivatives of the Tris(2,2‘-bipyridyl) Ruthenium(II) Complex

Abstract

Light-emitting devices from the tris(2,2‘-bipyridyl)ruthenium(II) complex [Ru(bpy)₃²⁺] and new derivatives thereof were prepared. Due to the electrochemical nature of the device operation, single-layer devices in an ITO/ Ru(bpy)₃²⁺ complex + PMMA/Ag sandwich configuration achieved very high external quantum efficiencies. The derivatives of the Ru(bpy)₃²⁺ complex were designed and synthesized to inhibit self-quenching of the excited state by adding different alkyl substituents on the bipyridyl ligands. As a result, devices that contain these new Ru(bpy)₃²⁺ complexes show a higher photoluminescence and electroluminescence efficiency than devices made from the unmodified Ru(bpy)₃²⁺ complex. External quantum efficiencies up to 5.5% at brightnesses in the range of 10−50 cd/m² are reported. In addition, the response time of such devices (which is a result of the electrochemical operation) has been shortened dramatically. An “instantaneous” light emission is achieved for devices that employ smaller counterions such as BF₄^- to increase the ionic conductivity. Such a device shows a response time of less than 1 s to emit 10−20 cd/m² after the operating voltage of 2.4 V has been applied.