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

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 WO3/Al/Al:Ag anode with the sheet resistance of 1.93 Omega/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 cm2 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.