Enhanced Triplet-Triplet Annihilation of Blue Fluorescent Organic Light Emitting Diode by Generating Excitons in Trapped Charge Free Regions

Three new anthracene cored molecules, 3,3'-(5-(10-(naphthalen-1-yl)anthracen-9-yl)-1,3-phenylene)dipyridine (AP3Py-Na), 3,3'-(5-(10-(naphthalen-2-yl)anthracen-9-yl)-1,3-phenylene)dipyridine (AP3Py-2Na), and 9,10-bis(3,5-di(pyridin-3-yl)phenyl)anthracene (ADP3Py), were synthesized to use as an efficiency enhancement layer (EEL) in blue fluorescent organic light emitting diodes (OLEDs). Insertion of a very thin EEL (3 nm) between the deep blue emitting layer (EML) and the electron transport layer (ETL) enhanced the external quantum efficiency (EQE) of the blue device by 44% compared to the device without the EEL, resulting in an external quantum efficiency of 7.9% and a current efficiency of 9.0 cd A‒1 at 1,000 cd m‒2; the CIE coordinates of the emitting color were (0.13, 0.14). The transient electroluminescence showed that the efficiency enhancement originates from the triplet-triplet annihilation (TTA) process in the EEL, followed by energy transfer to the emitting dye in the emitting layer.