Efficient red electroluminescent devices with very low operation voltage by utilizing hole and electron transport materials as the host

In this work, we report high performance red electroluminescent (EL) devices with very low operation voltage based on iridium complex iridium()bis(2-phenylquinoly-N,C²′)-dipivaloylmethane (PQ₂Ir(dpm)) by utilizing hole transport material di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) and electron transport material 1,3,5-tris(6-(3-(pyridine-3-yl)phenyl)pyridine-2-yl) (Tm3PyP26PyB) as host materials. A series of simplified devices with single or double light-emitting layer(s) (EML(s)) were fabricated and examined. The advantages of this design strategy can be summarized as follows: (i) easier injection and transport of holes and electrons, (ii) broadening recombination zone, and (iii) balanced carriers' distribution. Finally, efficient red EL device with highest current efficiency, power efficiency, external quantum efficiency (EQE) and brightness up to 40.59 cd/A, 47.20 lm/W, 14.7% and 34280 cd/m², respectively, was realized. Excitedly, the operation voltage was only 2.4 V at the brightness of 1 cd/m². Even at high brightness of 1000 cd/m² (3.5 V), current efficiency as high as 36.34 cd/A (EQE = 13.1%) can still be retained by the same device. Devices with such low operation voltage are of great significance for the industrialization of organic light-emitting diodes (OLEDs).