Cubic- and Hexagonal-Phase MgZnO Nanoparticles for Electron Transport Layers in Electroluminescent Quantum-Dot Light-Emitting Diodes

Abstract

Magnesium-doped zinc oxide (MZO) nanoparticles (NPs) with a cubic zinc blende (ZB) structure and with a hexagonal wurtzite (WZ) structure were prepared via a wet-chemical synthetic process by varying the base and used as the electron transport layer (ETL) for electroluminescent (EL) quantum-dot light-emitting diodes (QLEDs). Both as-synthesized MZO NPs were monodisperse with a polydispersity index <0.15 and retained excellent colloidal stability at least for 4 weeks. The formation of a NP film from the MZO NPs to configure the architecture of EL QLEDs resulted in significant enhancement in the charge carrier transport and the EL performance of QDs. It was found that the cubic MZO has more improvement than the hexagonal one on the EL device current density and current efficiency. Furthermore, considering the efficient recombination of electron and hole carrier transport, the conductive molecule tris(4-carbazoyl-9-ylphenyl)amine (TCTA) was added to poly(9-vinylcarbazole) (PVK) to increase the hole mobility. As a result, the EL QLEDs equipped with the combination of cubic MZO/TCTA-PVK carrier transport layers show 5-fold device efficiency and 10-fold brightness as high as 234,400 cd/m2, compared with conventional ZnO/PVK-based devices. This work highlights the potential of the cubic ZB-phase-based MZO film as the electron transport layer and TCTA mixed PVK in developing a solution for high-performance QLEDs.

Enhanced Carrier Mobility by Doping NaCl in a Hole-Transport Layer for Electroluminescent Quantum Dots Light-Emitting Diodes

“…It has been reported that the device operational time could be improved by more efficient electron–hole injection into the QD emitting layer (EML) . On the other hand, it was reported that a carrier-transport layer with appropriate roughness could improve the charge injection, so improved reliability of the NaCl-doped PVK HTL might also be related to enhanced carrier injection. Parts b and c of Figure present the turn-on voltage and current efficiency data of QLEDs with various NaCl doping contents.…”

“…The device data are summarized in Table . In this work, QDs with a relatively thicker shell are employed in the devices, which exhibit much higher current density than conventional QDs with a thinner shell. − These types of QDs can be driven to exhibit high brightness but with relatively lower external quantum efficiency (EQE) because of higher current consumption. After the introduction of a NaCl-doped PVK HTL, the device efficiency obviously increases, and the driving voltage decreases as well.…”

Advancements in semiconductor quantum dots: expanding frontiers in optoelectronics, analytical sensing, biomedicine, and catalysis

“…15–17 They have also tried to use CQD films as an active material for field effect transistors 18 and solar cells, 19 and as a self-emitting layer for the CQD-electroluminescence (EL) device structure. 20 With their massive Stokes shift, strong photoluminescence quantum yield (PLQY), and high extinction coefficient across a broad-spectrum range, CQDs are becoming a more popular choice in science for use in a wide range of optoelectronic device designs. 21 Recent advances in CQD nanotechnology have also slowly introduced these nanomaterials into analytical areas mostly as chemical sensors in fluorescence-based measurements.…”