Cationic cyclometallated iridium (iii) complexes

Over the past two decades dramatic advances have been achieved in the field of organic electroluminescent devices, for display and lighting applications. A recent development in this field involves the use of ionic transition metal complexes (iTMCs) that have shown the possibility to fabricate single layer electroluminescent devices, named Organic Light-emitting Electrochemical Cells (OLECs) [1]. This type of device represents an interesting possible alternative to the more investigated organic light- emitting diodes (OLEDs). In OLECs, the charged complexes support all three processes of charge injection, charge transport and emissive recombination. Therefore, no additional layers are needed in the device and the emissive layer can be solution processed, which makes industrial manufacturing easier. At the moment, the most common cationic complexes are based on iridium, ruthenium, osmium, platinum, and copper [2]. Here we present a study on the use of three different cationic iridium(III) complexes [3,4] (Figure 1) in luminescent single layer devices in the presence and in the absence of an ionic liquid (IL). The complex [Ir(ppy)2(5-CH3-1,10-phen)][PF6] (ppy = 2-phenylpyridine, phen = phenanthroline) reaches the most efficient results compared to the other ones. It has a very competitive brightness of 3040 cd/m2, obtained at 8V. The presence of IL lowers the turn-on time, and therefore, the operation voltage of the device at 3V. However, from the other side, the enhancement of the ions concentration into the film reduces the device lifetime t1/2, which is one of the main concern in light emitting devices. 1. J. Slinker, S. Bernhard, G. G. Malliaras et al., J. Mater. Chem., 17 (2007) 2976-2988. 2. L. De Cola, C. Bizzarri, M. Mydlak et al., Adv. Funct. Mater., 20 (2010) 1812–1820. 3. C. Dragonetti, D. Roberto, A. Valore et al., Inorg. Chem, 46 (2007) 8533-8547. 4. C. Dragonetti, D. Roberto, A. Valore et al., J.Phys. Chem. C, 113 (2009) 12517–12522.