Double-Heterojunction Nanorod Light-Emitting Diodes with High Efficiencies at High Brightness Using Self-Assembled Monolayers

Size-tunable, narrow-bandwidth emission, low threshold voltage, and high external quantum efficiency (EQE) make quantum dot light-emitting diodes (QD-LEDs) promising in next-generation display and lighting technologies. However, the maximum efficiencies are often observed in a relatively low-current, low-brightness regime, and the efficiency droop leads to less-than-ideal performance at high-luminance conditions useful for many applications. Here, we examine solution-processed, double-heterojunction nanorod (DHNR)-LEDs with self-assembled monolayer (SAM) modified indium tin oxide (ITO) electrodes. The SAMs can modify the surface and the work function of ITO, facilitate hole transport into the device, and therefore improve charge balance in DHNR-LEDs. Extremely bright DHNR-LEDs with maximum luminance over 100 000 cd/m² are demonstrated. Furthermore, maximum efficiencies appear at high luminance conditions that can be achieved at very low bias and current density (e.g., 3.1 V and 53 mA/cm² at ∼10 000 cd/m², corresponding to EQE = 10.7%, current efficiency = 21.7 cd/A, and luminous power efficacy = 19.5 lm/W). Despite the fact that DHNRs have only about half the photoluminescence quantum yield of core/shell QDs, the achieved efficiencies at high luminance conditions are comparable to or surpass those demonstrated by the state-of-the-art QD-LEDs.