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We developed inverted red quantum dot light-emitting diodes (QLEDs) with ZnO nanoparticles synthesized in open and closed systems. Wurtzite-structured ZnO nanoparticles were synthesized using potassium hydroxide and zinc acetate dihydrate at various temperatures in the open and closed systems. The particle size increases with increasing synthesis temperature. The ZnO nanoparticles synthesized at 50, 60, and 70 °C in the closed system have an average particle size of 3.2, 4.0, and 5.4 nm, respectively. The particle size is larger in the open system compared to the closed system as the methanol solvent evaporates during the synthesis process. The surface defect-induced emission in ZnO nanoparticles shifts to a longer wavelength and the emission intensity decreases as the synthesis temperature increases. The inverted red QLEDs were fabricated with a synthesized ZnO nanoparticle electron transport layer. The driving voltage of the inverted QLEDs decreases as the synthesis temperature increases. The current efficiency is higher in the inverted red QLEDs with the ZnO nanoparticles synthesized in the closed system compared to the devices with the nanoparticles synthesized in the open system. The device with the ZnO nanoparticles synthesized at 60 °C in the closed system exhibits the maximum current efficiency of 5.8 cd/A. [ABSTRACT FROM AUTHOR]

This paper presents a study that aims to enhance the performance of quantum dot light-emitting didoes (QLEDs) by employing a solution-processed molybdenum oxide (MoOx) nanoparticle (NP) as a hole injection layer (HIL). The study investigates the impact of varying the concentrations of the MoOx NP layer on device characteristics and delves into the underlying mechanisms that contribute to the observed enhancements. Experimental techniques such as an X-ray diffraction and field-emission transmission electron microscopy were employed to confirm the formation of MoOx NPs during the synthesis process. Ultraviolet photoelectron spectroscopy was employed to analyze the electron structure of the QLEDs. Remarkable enhancements in device performance were achieved for the QLED by employing an 8 mg/mL concentration of MoOx nanoparticles. This configuration attains a maximum luminance of 69,240.7 cd/cm2, a maximum current efficiency of 56.0 cd/A, and a maximum external quantum efficiency (EQE) of 13.2%. The obtained results signify notable progress in comparison to those for QLED without HIL, and studies that utilize the widely used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) HIL. They exhibit a remarkable enhancements of 59.5% and 26.4% in maximum current efficiency, respectively, as well as significant improvements of 42.7% and 20.0% in maximum EQE, respectively. This study opens up new possibilities for the selection of HIL and the fabrication of solution-processed QLEDs, contributing to the potential commercialization of these devices in the future. [ABSTRACT FROM AUTHOR]

Herein, the outstanding efficiency of solution‐processed quantum‐dot (QD) light‐emitting diodes (QLEDs) is demonstrated, which is achieved by adjusting the thickness of their Zn0.9Mg0.1O nanoparticle (NP) electron transport layer (ETL).The NPs are prepared by the sol‐gel method. As the thickness increases, the current density of the QLEDs decreases because of the increased resistance of the Zn0.9Mg0.1O NP ETL. As the thickness increases from 10 to 35 nm, the luminance, luminous efficiency, and external quantum efficiency (EQE) also increase because of the improved charge balance between electrons and holes in the QD emissive layer (EML). In contrast, as the thickness increases beyond 35–120 nm, these three variables decrease because of the worsening charge balance, which is attributing to deficient electron injection from the cathode into the QD EML compared with hole injection from the anode into the EML. The QLED with a 35 nm thick Zn0.9Mg0.1O NP ETL exhibits the highest luminance, luminous efficiency, and EQE, with values of 128 084 cd m−2, 88.8 cd A−1, and 21.3%, respectively. The superior device performance and good charge balance to the appropriate ETL thickness are attributed. [ABSTRACT FROM AUTHOR]

We developed highly efficient quantum dot light-emitting devices (QD-LEDs) by improving the charge balance with triple hole injection and transport layers consisted of MoO3/poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD)/poly(9-vinylcarbazole) (PVK). The hole injection layer was prepared by evaporating MoO3. Poly-TPD and PVK were spin-coated as hole transport layers. The stepwise energy level of MoO3/poly-TPD/PVK enhanced the hole injection from anode to QD emitters. Tris[2,4,6-trimethyl-3-(pyridine-3-yl)phenyl]borane (3TPYMB) was used as an electron transport layer (ETL) because of its relatively high electron mobility and deep lowest unoccupied molecular orbital (LUMO) level. We achieved high external quantum efficiency of 8.2% by enhancing hole injection into the QD layer in the organic ETL-based green QD-LEDs. [ABSTRACT FROM AUTHOR]

In this study, we fabricated QD-LEDs with QD emitters dispersed in poly(9-vinylcarbazole) (PVK) matrix. The emission layer was prepared by spin-coating of the PVK solution dispersed with red QD nanoparticles. The concentration of QDs was varied to be 0.5, 2.0, 5.0, and 10.0 mg/ml in PVK solution of 25 mg/ml. As the QD concentration increases, the current efficiency of QD-LED gradually increases and the emission from PVK matrix decreases. In addition, we investigated energy transfer system with QD and organic dopant material using same structure in emissive layer. We obtained a maximum current efficiency of 4.1 cd/A and an external quantum efficiency of 3.0% were achieved at a QD concentration of 5.0 mg/ml in QD-LEDs. [ABSTRACT FROM AUTHOR]