The effect of various electrodes on the properties of electroluminescent devices with potassium chloride inside tris (8-hydroxyquinoline) aluminum

摘要

The performance of organic light-emitting diodes (OLED), based on NPB/Alq_3/KCl/Alq_3 active regions, with various anode (i.e. ITO and 1TO/MOO_3) and cathode (i.e. Al and LiF/Al) structures is compared. NPB, Alq_3, KC1, ITO, MoO_3, Al and LiF are N,N'-bis-(l-naphthl)-diphenyl-l,l'-biphenyl-4,4'-diamine, tris (8-hydroxyquinoline) aluminum, potassium chloride, indium-tin oxide, molybdenum trioxide, aluminum and lithium fluoride, respectively. When bare Al is used as a cathode, both luminance and efficiency are improved by the insertion of KC1 inside Alq3 (anode/NPB/Alq_3/KCl/Alq_3/Al), compared to a control device (anode/NPB/Alq_3/Al). This is attributed to trap sites induced by KC1 layer, which give a better recombination in the devices. However, if the cathode is LiF/Al, the performance of control device (anode/NPB/Alq_3/ LiF/Al) is superior to that of devices with KC1 inside Alq_3 (anode/NPB/Alq_3/KCl/Alq_3/LiF/Al), which is attributed that the probability of electron injection from cathode is decreased.