High-efficiency inverted quantum dot light emitting diodes with enhanced hole injection
Hybrid MoO3/HAT-CN is employed as the hole injection layers (HILs) in green inverted colloidal quantum dot light-emitting devices (QLEDs). The hybrid HILs can be easily prepared and are found to improve electroluminescent properties effectively. The best performance device has a HIL of 1.5 nm-thick MoO3/2.5 nm-thick HAT-CN and shows a turn-on voltage of 1.9 V, a maximum current efficiency (CEmax) of 41.3 cd A-1 and maximum external quantum efficiency of 9.72%. In comparison to the corresponding devices with the single MoO3 or HAT-CN interlayer, the CEmax is improved by 1.6 or 1.5 times, respectively. The measured electrical performance shows that hole-only devices with hybrid HILs have a smaller leakage current density at low driving voltage and much enhanced hole injection current than the devices with single interlayers. It indicates that much improved electroluminescent efficiency in green inverted QLEDs with Hybrid MoO3/HAT-CN orginates from the significant enhancement of hole injection efficiency and suppression of space change accumulation in quantum dot emitting region due to the improved balance of the charge carriers. The hybrid HILs can be extended to other color inverted QLEDs, which is favourable to a bright, high-efficient and color saturation devices for display applications.