Vacuum deposited WO3/Al/Al:Ag anode for efficient red organic light-emitting diodes

Abstract

Vacuum deposited multilayered electrode with ultra-smooth surface morphology and suitable work function for efficient electron or hole injection at the interface between the organic and metal layers is attracting more attentions recently. Following the trend, a simplified structure of WO 3 /Al/Al:Ag anode with the sheet resistance of 1.93 Ω/sq, work function of ∼5.11 eV, and surface roughness of 0.72 nm was fabricated to develop a red organic light-emitting diode (OLED) with the external quantum efficiency (EQE) of ∼16.18% at 1000 cd m −2 , which is much higher than that of an red OLED based on standard ITO electrode (EQE ∼ 12.32%). In addition, the red OLED with our proposed ITO-free anode exhibit a bright emission with luminance of >10,000 cd m −2 at 5 V as well as could be fabricated on a large active area of 4 cm 2 without any breakdown issue. This is attributed to the ultra-smooth multilayer with a suitable workfunction reducing the contact barrier energy in the interface of organic and metal layer. Impedance spectroscopy, transient electroluminescence, and optical simulation were carried out to understand the device physics and carrier recombination behaviors. In the present work, we have developed the ITO-free, red, and exciplex organic light-emitting diodes (OLEDs) demonstrating remarkably high EL efficiency and low turn-on voltage. The simplified structure of WO 3 /Al/Al:Ag anode with the sheet resistance of 1.93 Ω/sq, work function of ∼5.11 eV, and surface roughness of 0.72 nm was fabricated to develop a red organic light-emitting diode (OLED) with the external quantum efficiency (EQE) of ∼16.18% at 1000 cd/m 2 . • The ITO-free red phosphorescent organic light-emitting diodes (OLEDs) with a metal-alloy electrode was demonstrated. • The WO 3 /Al/Al:Ag anode with low resistance of 1.93 Ω/sq, work function of 5.11 eV, and smooth surface roughness of 0.72 nm. • The ITO-free OLEDs exhibit a bright emission with luminance of >10,000 cd m −2 at 5 V. • The external quantum efficiency (EQE) of ITO-free OLEDs achieved 16.18% at 1000 cd m −2 .