Correlation between external quantum efficiency and electrical characteristic according to concentration of sensitizer in hyper-fluorescent oleds��

Abstract

We analyzed the change of electrical characteristics of hyperfluorescence OLED according to the doping concentration using Modulus spectroscopy. As the concentration of the thermally activated delayed fluorescence (TADF) sensitizer increased, the turn-on voltage was reduced by forming a conductive path by the sensitizer. However, it was not related to the external quantum efficiency (EQE). The difference between the two trends can be understood from the electrical and photophysical perspectives such as Modulus spectroscopy, EL spectrum and capacitance-voltage (C-V) curve. The ratio of 5:1 device with the most suitable doping ratio showed the highest 14.86% of EQE and 46.82 cd/A of current efficiency (CE). The reason for this result is that the distance between the sensitizer and the dopant is most suitable considering the Förster energy transfer (FRET) radius. This contributed to the closest match between the point at which the maximum value of capacitance and the turn-on voltage of the device in the C-V curve. © 2020 SID.