Efficient inverted quantum-dot light-emitting devices with TiO_2/ZnO bilayer as the electron contact layer

Xu, Wei; Ji, Wenyu; Jing, Pengtao; Yuan, Xianglin; Wang, Y. A.; Xiang, Weidong; Zhao, Jianlong

doi:10.1364/ol.39.000426

Cited by 29 publications

(28 citation statements)

References 21 publications

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“…Thus, reduced efficiency, poor operational stability, and severe efficiency roll-off can be observed mostly in hybrid QLEDs. [22][23][24][25] Recently, a few strategies have been introduced to improve the charge balance. Among the methods, inserting a thin interlayer between the QD emission layer (EML) and the metal oxide ETL is a widely used and effective strategy to control excess electron injection into QDs.…”

Section: Introductionmentioning

confidence: 99%

Enhanced efficiency and high temperature stability of hybrid quantum dot light-emitting diodes using molybdenum oxide doped hole transport layer

et al. 2019

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Section: Introductionmentioning

confidence: 99%

Enhanced efficiency and high temperature stability of hybrid quantum dot light-emitting diodes using molybdenum oxide doped hole transport layer

et al. 2019

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“…This causes a build‐up of electrons in the QD layer, reducing the device efficiency due to rapid nonradiative Auger recombination or injection of electrons into the HTL . Approaches taken to reduce the build‐up of electrons in the QD film include selecting hole transport materials with smaller highest‐occupied‐molecular‐orbital (HOMO) energies, engineering the shell of the QDs to hinder electron injection, inserting the QD layer inside the HTL, or inserting a thin layer of insulating polymer or lower‐mobility TiO 2 between the QD and ETL to hinder charge injection. Despite these advances, the development of alternative approaches to balance charge injection, which do not require modification of the energy levels or architecture of the device, are needed to diversify the range of materials and device architectures available for use in QLEDs.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Quantum Dot LED Efficiency by Tuning Electron Mobility in the ZnO Electron Transport Layer

Kirkwood

Singh

Mulvaney

2016

Adv Materials Inter

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nanoparticle film, [7,11] the postdeposition film annealing temperature, [12] and the density of dopant ions in the ZnO NPs, [13,14] these works do not explain how the tunable electrical properties of ZnO nanoparticles themselves [15,16] may be exploited to enhance QLED performance.An important challenge arising from the architecture of QLEDs is balancing electron and hole injection into the thin QD layer. Due to the deep valence band energy of core-shell CdSe QDs, hole injection into a QD is expected to be less facile than electron injection. This causes a build-up of electrons in the QD layer, [4,7,17] reducing the device efficiency due to rapid nonradiative Auger recombination [18] or injection of electrons into the HTL. [19,20] Approaches taken to reduce the build-up of electrons in the QD film include selecting hole transport materials with smaller highest-occupied-molecular-orbital (HOMO) energies, [9] engineering the shell of the QDs to hinder electron injection, [17,[21][22][23] inserting the QD layer inside the HTL, [19,24] or inserting a thin layer of insulating polymer [4] or lower-mobility TiO 2[25] between the QD and ETL to hinder charge injection. Despite these advances, the development of alternative approaches to balance charge injection, which do not require modification of the energy levels or architecture of the device, are needed to diversify the range of materials and device architectures available for use in QLEDs.To this end, we have developed a method for balancing charge injection in QLED devices by tuning the electron mobility in the ZnO nanoparticle ETL without modification of the device architecture. This is achieved by employing a solution-phase annealing step prior to film deposition which, unlike postdeposition annealing steps, does not change the physical properties of the ZnO film such as thickness or density. In this way changes in the QLED performance can be unambiguously attributed to the measurable electrical properties of the ZnO film. The focus on the ZnO electron mobility is inspired by models of OLED devices which have demonstrated that the location of electron-hole recombination in a device is determined by the relative mobilities of holes and electrons. [26,27] In a QLED the QD film is typically 2-3 monolayers thick and so the position of recombination must be centered on this small region for maximum luminescence efficiency. Here, we show that the position of recombination and hence charge balance in the QD layer, varies with both electron mobility and device luminance. At the same time we address the need for Quantum-dot (QD) light-emitting diodes (QLEDs) are an important new class of optoelectronic device. Despite the ubiquity of ZnO as the electrontransport material in QLEDs, little is known about how its properties influence QLED performance. Here, it is demonstrated that the defect density and electron mobility of the ZnO nanoparticle electron-transport layer strongly affect QLED device efficiency and can be used to balance electron and hole injection into the QD l...

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“…So, they are attractive as chromophores in LEDs. Thus recently, quantum dot based light emitting diodes (QLEDs) became competitive alternatives to organic light emitting diodes (OLEDs) in terms of colour purity, luminescence intensities, and external quantum efficiencies (EQEs) [121][122][123] The narrow emission profile, the high stability of quantum dots (QDs), the high photoluminescence quantum yields (PL QYs), and the easily tunable emission wavelengths make them attractive as quantum dot LEDs (QLED) [124]. By understanding the basic device physics and optimizing the device structure it was possible to improve the device performance and efficiency of QLEDs, so much that they can be compared to organic LEDs [122,[125][126][127][128][129][130][131][132][133].…”

Section: Qd-ledsmentioning

confidence: 99%

Polymer Coated Semiconducting Nanoparticles for Hybrid Materials

Zentel

2020

Inorganics

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This paper reviews synthetic concepts for the functionalization of various inorganic nanoparticles with a shell consisting of organic polymers and possible applications of the resulting hybrid materials. A polymer coating can make inorganic nanoparticles soluble in many solvents as individual particles and not only do low molar mass solvents become suitable, but also polymers as a solid matrix. In the case of shape anisotropic particles (e.g., rods) a spontaneous self-organization (parallel orientation) of the nanoparticles can be achieved, because of the formation of lyotropic liquid crystalline phases. They offer the possibility to orient the shape of anisotropic nanoparticles macroscopically in external electric fields. At least, such hybrid materials allow semiconducting inorganic nanoparticles to be dispersed in functional polymer matrices, like films of semiconducting polymers. Thereby, the inorganic nanoparticles can be electrically connected and addressed by the polymer matrix. This allows LEDs to be prepared with highly fluorescent inorganic nanoparticles (quantum dots) as chromophores. Recent works have aimed to further improve these fascinating light emitting materials.

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Efficient inverted quantum-dot light-emitting devices with TiO_2/ZnO bilayer as the electron contact layer

Cited by 29 publications

References 21 publications

Enhanced efficiency and high temperature stability of hybrid quantum dot light-emitting diodes using molybdenum oxide doped hole transport layer

Enhanced efficiency and high temperature stability of hybrid quantum dot light-emitting diodes using molybdenum oxide doped hole transport layer

Enhancing Quantum Dot LED Efficiency by Tuning Electron Mobility in the ZnO Electron Transport Layer

Polymer Coated Semiconducting Nanoparticles for Hybrid Materials

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