Highly efficient and all-solution processed quantum dot light-emitting diodes (QLEDs) with high performance are demonstrated by employing ZnMgO nanoparticles (NPs) with core/shell structure used as an electron transport layer (ETL). Mg-doping in ZnO NPs exhibits a different electronic structure and degree of electron mobility. A key processing step for synthesizing ZnMgO NPs with core/shell structure is adding Mg in the solution in addition to the remaining Mg and Zn ions after the core formation process. This enhanced Mg content in the shell layer compared with that of the core X-ray photoelectron spectroscopy showed a higher number of oxygen vacancies for the ZnMgO core/shell structure, thereby enhancing the charge balance in the emitting layer and improving device efficiency. The QLED incorporating the as synthesized ZnMgO NP core/shell A exhibited a maximum luminance of 55,137.3 cd/m2, maximum current efficiency of 58.0 cd/A and power efficiency of 23.3 lm/W. The maximum current efficiency and power efficiency of the QLED with ZnMgO NP core/shell A improved by as much as 156.3% and 113.8%, respectively, compared to the QLED with a Zn0.9Mg0.1O NP ETL, thus demonstrating the benefits of ZnMgO NPs with the specified core/shell structure.
This paper presents a study aimed at enhancing the performance of quantum dot light-emitting didoes (QLEDs) by employing a solution-processed molybdenum oxide (MoO3) nanoparticle (NP) as a hole injection layer (HIL). The study investigates the impact of varying the concentrations of the MoO3 NP layer on device characteristics and explores the underlying mechanisms responsible for the observed enhancements. Experimental techniques such as an X-ray diffraction and field-emission transmission electron microscopy were employed to confirm the formation of MoO3 NPs during the synthesis process. Ultraviolet photoelectron spectroscopy is employed to analyze the electron structure of the QLEDs. The QLED with an 8 mg/mL concentration of MoO3 nanoparticles achieves remarkable improvements in device performance, with a maximum luminance of 69,240.7 cd/cm2, maximum current efficiency of 56.0 cd/A, and maximum external quantum efficiency (EQE) of 13.2%. The obtained results signify a notable progress in comparison to QLED without HIL and those utilizing the widely used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) HIL. They exhibit a remarkable enhancement of 59.5% and 26.4% in maximum current efficiency, respectively, as well as a significant improvement 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.
Zn0.9Mg0.1O nanoparticle (NP) were employed as electron transport layers (ETLs) with varying thicknesses to investigate their influence on the efficiency of the top-emission quantum dot light-emitting diodes (TE-QLEDs) fabricated inside the bank. An increase in the thickness of the Zn0.9Mg0.1O NP ETL led to a decrease in the concentration of oxygen vacancies, reducing the conductivity of the Zn0.9Mg0.1O and resulting in lower current density in the TE-QLEDs. The decrease in conductivity of Zn0.9Mg0.1O NP ETL was confirmed through electron-only device (EOD) characterization. Furthermore, it was noted that when the thickness of Zn0.9Mg0.1O NP ETL was 30 nm, the concentration of hydroxyl species reached its minimum. By minimizing the presence of hydroxyl species, exciton quenching at the quantum dot (QD) and Zn0.9Mg0.1O NP ETL interface was minimized, enhancing charge balance within the QD, significantly improving the efficiency of QLED. We successfully demonstrated that TE-QLED with a 30 nm-thick Zn0.9Mg0.1O NP ETL exhibits outstanding performance, achieving a maximum current efficiency of 91.92 cd/A and a maximum external quantum efficiency of 21.66%. These results suggest that Zn0.9Mg0.1O NP ETL, when tailored to an appropriate thickness, can serve as an ETL for TE-QLEDs, effectively suppressing exciton quenching and enhancing the charge balance in the TE-QLEDs.
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.
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 Zn 0.9 Mg 0.1 O 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 Zn 0.9 Mg 0.1 O 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 Zn 0.9 Mg 0.1 O 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.
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