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

The performance of organic light-emitting diodes (OLED), based on NPB/Alq3/KCl/Alq3 active regions, with various anode (i.e. ITO and ITO/MoO3) and cathode (i.e. Al and LiF/Al) structures is compared. NPB, Alq3, KCl, ITO, MoO3, Al and LiF are N,N′-bis-(1-naphthl)-diphenyl-1,1′-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 KCl inside Alq3 (anode/NPB/Alq3/KCl/Alq3/Al), compared to a control device (anode/NPB/Alq3/Al). This is attributed to trap sites induced by KCl layer, which give a better recombination in the devices. However, if the cathode is LiF/Al, the performance of control device (anode/NPB/Alq3/LiF/Al) is superior to that of devices with KCl inside Alq3 (anode/NPB/Alq3/KCl/Alq3/LiF/Al), which is attributed that the probability of electron injection from cathode is decreased.

Research highlights
► We examine the effect of electrode on the performance of OLED with KCl inside Alq3.
► The anode includes ITO and ITO/MoO3; the cathodes are Al and LiF/Al.
► The cathode has a great influence on the improving properties of KCl inside Alq3.
► The enhancing properties of KCl in OLED are unsusceptible to the anode.
► KCl has two effects: trap hole; decrease the probability of electron injection.