Exciplex-Forming Co-Host-Based Red Phosphorescent Organic Light-Emitting Diodes with Long Operational Stability and High Efficiency

The use of exciplex forming cohosts and phosphors incredibly boosts 100 the efficiency of organic light-emitting diodes (OLEDs) by providing a barrier-free charge injection into an emitting layer and a broad recombination zone. However, 80 most of the efficient OLEDs based on the exciplex forming cohosts has suffered from the short operational lifetime. Here, we demonstrated phosphorescent OLEDs 60 (PhOLEDs) having both high efficiency and long lifetime by using a new exciplex forming cohost composed of N,N'-diphenyl-N,N'-bis(1,1'-biphenyl)-4,4'-diamine 40 (NPB) and (1,3,5-triazine-2,4,6-triyOtris(benzene-3,1-diy1))tris (diphenylphosphine oxide) (PO-T2T). The red-emitting PhOLEDs using the exciplex forming cohost 20 achieved a maximum external quantum efficiency (EQE) of 34.1% and power efficiency of 62.21m W1- with low operating voltages and low efficiency roll-offs. More importantly, the device demonstrated a long lifetime around 2249 h from 1000 cd 111-2 to 900 cd m(-2) (LT90) under a continuous flow of constant current. The efficiencies of the devices are the highest for red OLEDs with an LT90 > 1000 h.