Efficiency enhancement of iridium-based organometallic light emitting diodes

The efficiency of the Organic Light Emitting Diode (OLED) is given either by the internal quantum efficiency of the organometallic compound or by the charge transport across OLED. IrQ(ppy)₂ is a new organometallic compound which gives green and red electroluminescence. This dual emitter compound exhibits a lower internal quantum efficiency compared with classical Ir(ppy)₃ green emitter because of a weak coupling between Ir³⁺ and oxygen ions which significantly reduces the charge transfer towards quinoline ligand. This lower internal quantum efficiency is compensated by the higher electron donor character of the quinoline ligand which induces better change transport in OLED structures. In the case of Ir(ppy)₃ green emitter, the efficiency can be improved by adding magnetic or metallic nanoparticles which significantly change the charge transport for the Ir(ppy)₃ based OLED structures. The metallic or magnetic nanoparticles embedded in the transparent and conductive polymer, reduce the electron injection, acting as filling traps, which directly increases the electroluminescence and the current at the same voltage. (paper)