Droop-Free Colloidal Quantum Dot Light-Emitting Diodes

Abstract

Colloidal semiconductor quantum dots (QDs) are a highly promising materials platform for implementing solution-processable light-emitting diodes (LEDs). They combine high photostability of traditional inorganic semiconductors with chemical flexibility of molecular systems, which makes them well-suited for large-area applications such as television screens, solid-state lighting, and outdoor signage. Additional beneficial features include size-controlled emission wavelengths, narrow bandwidths, and nearly perfect emission efficiencies. State-of-the-art QD-LEDs exhibit high internal quantum efficiencies approaching unity. However, these peak values are observed only at low current densities ( J) and correspondingly low brightnesses, whereas at higher J, the efficiency usually exhibits a quick roll-off. This efficiency droop limits achievable brightness levels and decreases device longevity due to excessive heat generation. Here, we demonstrate QD-LEDs operating with high internal efficiencies (up to 70%) virtually droop-free up to unprecedented brightness of >100,000 cd m (at ∼500 mA cm). This exceptional performance is derived from specially engineered QDs that feature a compositionally graded interlayer and a final barrier layer. This QD design allows for improved balance between electron and hole injections combined with considerably suppressed Auger recombination, which helps mitigate efficiency losses due to charge imbalance at high currents. These results indicate a significant potential of newly developed QDs as enablers of future ultrabright, highly efficient devices for both indoor and outdoor applications.

High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiOx Hole‐Injection Layers with a High and Stable Work Function

“…Quantum‐dot light‐emitting diodes (QLEDs) may fully exploit the superior optoelectronic properties and excellent solution processability of colloidal quantum dots (QDs), promising a new generation of high‐performance, large‐area, and low‐cost electroluminescence devices . State‐of‐the‐art QLEDs use the most effectively developed CdSe‐based core–shell QDs as emitters . A multilayer structure of transparent anode/hole‐injection layer (HIL)/hole‐transporting layer (HTL)/QDs emissive layer/oxide electron‐transporting layer (ETL)/metal cathode is generally adopted .…”

Effects of 1,2-ethanedithiol concentration on performance improvement of quantum-dot LEDs

“…Such traits have made colloidal QDs particularly promising candidates for next-generation displays and lighting systems, thus motivating many studies. [1][2][3][4][5][6][7][8][9] To this end, extensive efforts have been made to improve QD LED (QLED) performance toward the goal of simultaneously achieving high brightness, efficiency and durability.…”

Quantum‐Dot Light‐Emitting Diodes for Outdoor Displays with High Stability at High Brightness

“…The growth of the ZnSe/ZnSe 0.5 S 0.5 shell (≈2.3 nm ZnSe and ≈0.6 nm ZnSe 0.5 S 0.5 ) leads to a virtually continuously graded composition and stepwise change in the lattice spacing from the ZnCdSe core (4.5 nm) to the ZnS shell (≈0.3 nm) (Figure b,c), which translates into continuous and smooth conduction‐ and valence‐band confinement potentials, as illustrated in the energy diagram in Figure a. The design of the QD structure allows for a suppressed Auger recombination, which helps to mitigate efficiency losses due to charge imbalance, as demonstrated by Klimov and his co‐workers . It is important to note that, although both the electron and hole injection will be enhanced due to the spatially smooth band structures, ZnSe is chosen as the gi material mainly due to its shallower valence band compared with the widely used ZnS or CdS (Figure S6, Supporting Information), which is confirmed by ultraviolet photoemission spectroscopy (UPS) spectra, as shown in Figure d,e.…”