High-efficiency inverted quantum dot light-emitting diodes with enhanced hole injection.

Hybrid MoO/HAT-CN is employed as a hole injection layer (HIL) in green inverted colloidal quantum dot light-emitting devices (QLEDs). The hybrid HILs can be easily prepared and have been found to effectively improve the electroluminescent properties. The best performance device had an HIL of 1.5 nm-thick MoO/2.5 nm-thick HAT-CN and showed a turn-on voltage of 1.9 V, a maximum current efficiency (CE) of 41.3 cd A, and maximum external quantum efficiency of 9.72%. Compared to the corresponding devices with the single MoO or HAT-CN interlayer, the CE of the hole-only devices was 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 MoO/HAT-CN orginates from the significant enhancement of hole injection efficiency and suppression of space charge accumulation in the 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 are favorable to achieve bright, highly efficient, and color saturation devices for display applications.