Red and green inverted top-emitting quantum dot light-emitting diodes using CMOS-based electrodes for microdisplay applications

Abstract

Silicon (Si) substrates and complementary metal-oxide-semiconductor (CMOS) technology are being used in microdisplays in augmented reality/virtual reality devices owing to higher pixel resolution. Quantum-dot lightemitting diodes (QLEDs) incorporating colloidal quantum dots have emerged as promising devices for display applications owing to their exceptional color, high luminance, and solution processibility. However, studies on QLEDs on Si, particularly for microdisplay applications, remain limited. This study investigated the device characteristics of inverted top-emitting QLEDs using Si substrates and various CMOS process-based electrode materials (aluminum (Al), Al/titanium nitride (TiN), titanium, cobalt, and tungsten) for microdisplay applications. Devices incorporating a thin TiN layer on an Al electrode exhibited the highest efficiency and luminance compared to those with other electrodes. We successfully fabricated red and green inverted top-emitting QLEDs using microdisplay pixel-structured Al/TiN electrodes, with pixel pitch and fill factor of 10.8 mu m x 3.6 mu m and 72.5 %, respectively. Further, the device efficiency was optimized by changing hole and electron transport layer thicknesses, resulting in different efficiencies and electroluminescence spectra owing to the microcavity effect. Optical simulations demonstrated consistency with the measured values. Thus, the selection of the bottom electrode and a suitable design that considers the microcavity effect are crucial for high-performance QLEDbased microdisplays.