Efficient and Bright Colloidal Quantum Dot Light-Emitting Diodes via Controlling the Shell Thickness of Quantum Dots

Abstract

In this paper, we use a simple device architecture based on solution-processed ZnO nanoparticles (NPs) as the electron injection/transport layer and bilayer structure of poly(ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) as the hole injection/transport layer to assess the effect of shell thickness on the properties of quantum-dot-based light emitting diodes (QD-LEDs), comprising CdSe/CdS/ZnS core-shell QDs as the emitting layer. QDs with varying shell thickness were assessed to determine the best option of shell thickness, and the best improvement in device performance was observed when the shell thickness was 2.1 nm. Thereafter, different emissions of QDs, but with optimized same shell thickness (∼2.1 nm), were selected as emitters to be fabricated into same structured QD-LEDs. Highly bright orange-red and green QD-LEDs with peak luminances up to ∼30 000 and ∼52 000 cd m(-2), and power efficiencies of 16 and 19.7 lm W(-1), respectively, were demonstrated successfully. These results may demonstrate a striking basic prototype for the commercialization of QD-based displays and solid-state lightings.

The work mechanism and sub-bandgap-voltage electroluminescence in inverted quantum dot light-emitting diodes

“…Owing to these unique features, QDs have been actively investigated to utilize in many optoelectronic devices, for example, down-converters in backlit displays89, light-emitting diodes (LEDs)1011121314, lasers15, photodetectors16 and solar cells171819. Among these potential applications, the high-performance electrically driving QD-LEDs has been of particular interest due to their potential impact on display and lighting technologies.…”

“…As is well-known, there are two mechanisms proposed to explain the EL processes in QD-LEDs111213. For the first one, carriers transported through charge-transport layers are directly injected into QDs, where they can form excitons that then can radiatively recombine, as shown in Fig.…”

Bright, efficient, and color-stable violet ZnSe-based quantum dot light-emitting diodes

“…Considering the factors of the photopic luminosity function, the brightness and efficiency results of such violet QD-LEDs not only represent 12fold increase in device efficiency and extraordinary 100 times increase in luminance compared with previous Cd-free QD-LEDs but also can be much superior to the best performance (1.7 %) of their Cdbased violet counterparts. Different from our previous reports which using (poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) as HTLs, 16,42, 43 poly-N-vinylcarbazole (PVK) was chosen as the hole-transporting material and ZnO was used as the electrontransporting layers. Their excellent optical properties make them potential superstars in light-emitting diodes (LEDs) and displays.…”

“…Their excellent optical properties make them potential superstars in light-emitting diodes (LEDs) and displays. 4,42 The choices of HTL and ETL ensure the efficient injection of holes and electrons, which lead to an improved charge recombination within QD layer. Most of previous works on highly emissive and color-tunable QDs have been mainly concentrated on materials containing toxic cadmium, mercury, or lead.…”

Quantum Dot-Based Light Emitting Diodes (QDLEDs): New Progress

“…Optimizing the efficiency of devices can help to improve the performance of QDLEDs. Many researchers try to do their best in this respect such as Shen and his group [86]. They have suggested a new high efficiency QDLED.…”