Quantum Dot Light-emitting Diodes Research Articles

P‐158: Highly Flexible InP‐Based Quantum Dot Light‐Emitting Diodes Fabricated on Heat‐Dissipating Al‐Coated PEN Substrate

Quantum dot light‐emitting diodes (QLEDs) have garnered significant attention due to their outstanding optical and electrical properties. Furthermore, there have been many attempts to fabricate QLEDs on the flexible substrates for the application of wearable devices. However, flexible QLEDs face the challenge of instability under thermal heat, due to the low thermal conductivity of the substrates. In this study, we present the InP‐based QLEDs on 1 µm thick polyethylene naphthalate substrates, coated with aluminum for the heat dissipation. The coated Al layer can effectively dissipate the generated heat due to its high conductivity, while maintaining the flexibility of the substrates.

P‐162: Green solvent for fabricating inverted QD‐LED

Quantum‐dot light emitting diode (QD‐LED) displays have attracted great attention because of their high potential as a future display technology. The solution processability is also regarded as an important advantage for low‐cost manufacturing capabilities. However, the use of toxic and environmentally hazardous organic solvents is the dark side of solution processable QD‐LEDs. Chlorobenzene, chloroform, 1‐4 dioxane, and 1,2‐dichlorobenzene are representative toxic solvents for the manufacture of QD‐LEDs, and these are mainly used as solvents in the hole transport layer (HTL). Therefore, it is important to find an environmentally friendly solvent for (HTL). In this study, we report a new methodology for finding environmentally friendly solvents, that have good processability, and have solvent orthogonality with adjacent layers.

Enhancing CdSe/ZnS Quantum-Dot Light-Emitting Diode Performance: The Impact of Thermal Treatment Atmospheres on Fabrication Processes

We explored the thermal treatment impact on the performance of quantum-dot light-emitting diodes (QLEDs). The QLEDs comprised multiple layers: a 2.2-μm thick epoxy buffer layer; a bottom cathode composed of 12-nm MoOx/10-nm Ag/12-nm MoOx; a 20-nm ZnO electron transporting layer (ETL); a 10-nm CdSe/ZnS quantum dot light emission layer (EML); a 40-nm 4,4′,4″-Tris(carbazol-9-yl) triphenylamine hole transporting layer; a 10-nm WOx hole injection layer; and a 100-nm Ag top anode. We applied thermal treatments to the cathode, ETL, and EML separately to assess their effects on the QLEDs. Additionally, we evaluated the impact of the thermal treatment atmosphere. Vacuum thermal treatment on the cathode and EML resulted in minor improvements in QLED performance, whereas treatment of the ETL led to a decline in performance. In contrast, air thermal treatment on the cathode and EML decreased QLED performance but significantly improved it by 15% in current efficiency when applied to the ETL. The performance differences attributable to the thermal treatment atmosphere are likely due to ligand removal and oxidation processes, facilitated by thermal energy and oxygen. Our study highlights that air thermal treatment on the ETL substantially improves QLED performance, offering crucial insights into the significance of thermal treatment in QLED development.

20‐4: Efficient and Stable Red Quantum Dot Light‐Emitting Diode with Modified ZnMgO Nanoparticles

Since ZnO nanoparticles are employed as an electron transport layer in quantum dot light‐emitting diode (QLED), the electroluminescence efficiency of QLED is greatly boosted. However, the QLED stability still faces the challenge. Herein, we modify the ZnMgO nanoparticles with the thiol ligand, which can improve the efficiency and stability of QLED at the same time. As a result, the maximum external quantum efficiency of QLED is improved from 18.6% to 26.0%, accompanied by enhanced voltage sweep stability. Our work provides a practical method to enhance the performance of QLED.

28‐1: Invited Paper: Analyzing Charge Dynamics in Quantum Dot Light‐Emitting Diodes via Impedance Spectroscopy

The carrier dynamics in quantum dot light‐emitting diodes (QLEDs) significantly deviate from that in traditional organic and inorganic light‐emitting diodes. This study elucidates the charge injection and recombination processes in QLEDs using impedance spectroscopy. Parameters derived from the equivalent circuit model, in conjunction with the applied device voltage, elucidate the nuanced changes in carrier behavior during operation. This methodology serves as a potent tool and novel approach for comprehending and analyzing the physics of QLED devices.

P‐129: The Black Spot Phenomenon and Improvement in QLED Devices

In this paper, we studied the influence of ETL (electron transporting layer)and cathode material type as well as their interface on the performance of QLED (quantum dot light emitting devices). Through our research, we found that the black spot phenomenon of QLED device is strongly related to ETL material, and the number of black spots can be greatly reduced by improve ETL. In addition, the cathode material such as Ag and Al, also show their impact on black spots; Finally, one novel double‐layer ETL structure device was developed to avoid black spot, which manifest that the interaction between ETL and the electrode interface also play an important role. The absence of black spots in inverted devices also proves this conclusion.

P‐221: All Inkjet‐Printed Inverted Electroluminescent Quantum Dot Light Emitting Diode Display Based on Metal Oxide Thin Film Transistors

A 12.4‐inch inverted cadmium‐free electroluminescent quantum dot (QD) light emitting diode (LED) display panel based on metal oxide thin film transistors (TFTs) is demonstrated. The backplane of our panel is fabricated by using multiple steps of photolithography processes, and pixel/scan driver circuits are composed by n‐type indium‐gallium‐zinc oxide TFTs. Especially, each sub‐pixel has internal compensation circuit which compensates the threshold voltage of its own driving TFT. Different from the conventional structure, since our QD LEDs have inverted structures, electroluminescent layers from the electron injection layer to the hole injection layer are constructed by sequential inkjet‐printing processes. Our inverted electroluminescent QD LED display based on metal oxide TFTs is very promising structure for premium large‐format displays for the next generation due to its superb performance and cost‐effectiveness.

P‐164: Highly Efficient Quantum Dot Light‐emitting Diodes Enhanced via Ultraviolet Postprocessing

Recently, low efficiency and stability due to unbalanced carrier injection remain urgent problems in inorganic quantum dot light†emitting diodes (QLEDs). To address these issues, the device was irradiated with ultraviolet light in this study, which improved the interface contact. This resulted in the smaller electron potential barrier, increased hole injection and more balanced carrier injection in the device. Ultimately, the device efficiency was improved, and the operating lifetime of the device was increased by ~91†fold.

44‐3: High Efficiency and Brightness Quantum Rods Light Emitting Diode

Despite substantial efforts, the maximum external quantum efficiency (EQE) of red, green, and blue quantum dots remains close to 25%, limited by the outcoupling efficiency of specific device optical structures. Further improvements have primarily focused on optimizing light management. In this study, we employed rod‐shaped nanocrystals instead of sphere‐like quantum dots as the light‐emitting layer. The theoretical device outcoupling efficiency significantly increased to nearly 41% due to the intrinsic horizontal dipole alignment within the quantum rod film, nearly doubling the efficiency compared to quantum dot light‐emitting diodes (QDLEDs). As a result, we achieved record‐high EQEs of 14.1% for green quantum rod light‐emitting diodes, with maximum brightness exceeding 150,000 cd/m 2 , respectively. Our research demonstrates the immense potential of QRLEDs for display and lighting applications, paving a new way for the commercialization of nanocrystal particles.

28‐3: Analytic Model of Quantum Dot LED Current‐Voltage Characteristics

Quantum dot light‐emitting diode (QDLED) displays promise superior color gamut with respect to organic light‐emitting diode (OLED) displays and liquid‐crystal displays (LCDs). In this paper, for the first time, a data‐validated closed‐form physics‐based expression is derived for the I‐V characteristics of QDLEDs. The I‐V equation is derived using an approximation scheme which not only brings the previouslyintractable transport mechanisms back into the fold of analytic tractability but emphasizes the underlying physics of each transport mechanism in doing so. The model is shown to fit state‐of‐the‐art experimental data over a large range of operating currents. The model may be used for circuit simulations.

44‐1: Top‐Emitting Quantum‐Dot Light‐Emitting Diodes with Rainbow Emission Color and Their Application in Anti‐Counterfeiting Recognition

We have successfully developed an advanced and highly secure anti‐counterfeiting device based on quantum‐dot light‐emitting diodes (QLEDs). This novel device exhibits several key attributes, including affordability, non‐replicability, ease of detection, and exceptional security. By incorporating both electroluminescence and photoluminescence modes, our device offers versatility in satisfying different levels of anti‐counterfeiting needs. To enhance its security further, we have integrated physically unclonable functions (PUFs) and combined them with a pattern recognition system. This integration ensures the device's uniqueness and enables it to meet the most stringent anti‐counterfeiting requirements. The achieved results demonstrate the significant potential of our device in combating counterfeiting and safeguarding various industries.

28‐5: Late‐News Paper: Investigation on Enhanced Performance of All†solution Inverted Quantum Dot Light Emitting Diode via Changing a Solvent

In inverted quantum‐dot light‐emitting‐diodes (QD‐LED), it is important to use orthogonal solvent for hole‐transport layer(HTL). In addition, modulating work function of each layer is good way to enhance carrier injection barrier. In this research, we confirmed the viability of usage of a solvent, named gamma‐valerolactone (GVL) for forming hole transport layer (HTL). By using the solvent, current density, luminance, roll‐off characteristics were enhanced, and highest occupied molecular orbital (HOMO) level was changed, which can enhance the hole injection.

High-efficiency red perovskite quantum dot light-emitting diodes via an effective cation exchange method for tunable emission wavelength

The utilization of perovskite quantum dots (PQDs) in photoelectric devices is indeed an area of intense research due to their advantageous properties such as tunability of visible light and efficient light emission. In this study, mixed CsPbI3 and FAPbI3 PQD dispersions were successfully employed for cation exchange to prepare red-color Cs1−xFAxPbI3 PQD with the photoluminescence (PL) wavelength from 689 nm (x = 0) to 778 nm (x = 1). It is also found that the aggregation of Cs1−xFAxPbI3 PQD films were strongly dependent on x. When x from 0 to 0.6, the holes in PQD thin films were gradually improved. On the opposite, when x > 0.6, the PQDs thin films returned more and more holes due to an excess of FA + cations. The resulting Cs1-xFAxPbI3 PQD based light-emitting diodes (LEDs) also demonstrated tunable emission wavelengths, and it is worth mentioning that the maximum external quantum efficiency (EQE) of 11.22 % was achieved with an emission wavelength of 758 nm when x = 0.6.

Dewetting-assisted inkjet printing and optimized solvent mixture of Cd-free InP quantum dots for high-resolution pixel-pattern

Direct-printed quantum dot (QD) patterns utilizing inkjet method are a next-generation alternative to achieve high-resolution quantum dot light-emitting diodes (QLED). However, research on high-resolution pixel patterns is still limited due to issues such as thickness uniformity. In this study, we explored the feasibility of direct printing QLEDs to attain high-resolution pixel-patterned displays. Here, we successfully fabricated arrays of green QLED devices with a resolution of 200 pixels per inch, employing a precise 1 pL fine printer nozzle and optimizing ink formulation to achieve superior surface roughness and uniformity at the desired thickness. The inkjet-printed QD layers demonstrated a surface roughness of 1.9 nm and a flatness ratio of 0.2, comparable to those achieved through conventional spin-coating processes. This investigation offers the potential for extending the methodology to the fabrication of cost-effective, high-resolution full-color QLED displays.

Well-type thick-shell quantum dots combined with double hole transport layers device structure assisted realization of high-performance quantum dot light-emitting diodes

Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation lighting and displays. Considering the optimization design of both the QD and device structure is expected to improve the QLED's performance significantly but has rarely been reported. Here, we use the thick-shell QDs combined with a dual-hole transport layer device structure to construct a high-efficiency QLED. The optimized thick-shell QDs with CdS/CdSe/CdS/ZnS seed/spherical quantum well/shell/shell geometry exhibit a high photoluminescence quantum yield of 96% at a shell thickness of 5.9 nm. The intermediate emissive CdSe layer with coherent strain ensures defect-free growth of the thick CdS and ZnS outer shells. Based on the orthogonal solvents assisted Poly-TPD&PVK dual-hole transport layer device architecture, the champion QLED achieved a maximum external quantum efficiency of 22.5% and a maximum luminance of 259955 cd m-2, which are 1.6 and 3.7 times that of thin-shell QDs based devices with single hole transport layer, respectively. Our study provides a feasible idea for further improving the performance of QLED devices.

Hybrid Design of Light‐Emitting Diodes in Tandem Structures

AbstractOrganic light‐emitting diodes in tandem structures (TOLEDs) have long been an effective strategy to realize multifold increased electroluminescence (EL) efficiency relative to the single‐unit OLEDs, making TOLEDs promising candidates for lighting and display applications. Benefitted from the development of organic emitters, hybrid tandem OLEDs (HTOLEDs) composing two or more types of OLED emitters (phosphorescence, fluorescence, and thermally‐activated delayed fluorescence (TADF)) are developed. The different energy conversion processes of these emitters can facilitate manipulated exciton distribution inside the device, leading to enhanced device performance. On the other hand, different emission technologies can also be integrated to form another kind of hybrid tandem light‐emitting diodes (HTLED) thanks to the compatibility of OLEDs with quantum dot LEDs (QLEDs) and perovskite LEDs (PeLEDs). In this review, the performance of different types of HTOLEDs and HTLEDs is comprehensively reviewed particularly focusing on the exciton regulations and manipulation of emission spectra in the sub‐units, aiming to provide guidelines for the EL performance optimization of HTOLEDs.

Application of quantum dot light-emitting diode harvest by quantum dot solar cells

Recent progress in photovoltaic (PV) cell usage has been hindered due to a shortage of suitable materials that emit adequate wavelengths of light energy and convert it to electricity. Quantum dot light-emitting diodes (QLEDs) and quantum dot solar cells (QDSCs) have been identified as promising artificial light sources and PV cell types to nicely fit into this solution, not only complying with that but also being controllable, flexible, portable, and lightweight. The purpose of this study is to provide a review of the application of how QLEDs can be collected for QDSCs. First, we introduce QLEDs as artificial light sources, briefly outline their mechanics and benefits, and compare them to other light sources for QDSC harvesting. Then, we summarize the mechanisms that occur when a QDSC absorbs a photon from a QLED, as well as how these energy flow pathways influence artificial light energy harvest. Finally, we explore the optoelectronic properties of lead sulphide (PbS) and lead selenide (PbSe) as appropriate quantum dots (QDs) materials for current applications in QDSC and QLED technologies. We anticipate that the literature will be comprehensive and relevant to the scientific community interested in creating artificial light energy harvesting and thus researching the most recent alternative method of getting healthy energy.

Highly enhanced Quantum dot light-emitting diode performance by controlling energy resonance in inorganic insertion layers

Quantum-dot light-emitting diodes (QLED) have become a research trend in the field of new displays due to their low cost, wide color gamut, narrow bandwidth, and characteristics that enable production through the solution-gel method. However, the electrical performance of QLED is consistently constrained by energy losses and imbalanced charge carrier injection. This motivates our focus on exciton recombination and energy losses within the quantum-dot layer to enhance the electrical efficiency of QLED. In this work, we introduce a method using a CdZnS quantum dot (B-QD) interlayer to modulate energy transfer and charge carrier transport in QLED devices employing CdSe quantum dot (G-QD) as the emissive layer. By strategically incorporating a B-QD layer between the G-QD and HTL/ETL, we facilitate energy transfer due to the overlap between the excitation wavelength of B-QD and the absorption wavelength of G-QDs. This leads to enhanced energy injection in QLED devices, resulting in a high current efficiency of 39.54 Cd/A and a peak brightness of 522,272 cd/m2 for efficient QLED. The corresponding external quantum efficiency (EQE) is greatly improved from 5.62 % to 9.4 %. Our work provides a straightforward and effective approach to modulate exciton recombination and energy injection and further can be applicable to other photo-electronics devices.

Solution‐Processed Tandem Quantum‐Dot Light‐Emitting Diodes with Dual Charge Generation Interfaces: Achieving Over Threefold Efficiency Enhancement

AbstractDespite the commercialization of thermally evaporated tandem organic light‐emitting diodes (OLEDs), challenges remain for solution‐processed tandem quantum‐dot light‐emitting diodes (QLEDs), including low efficiency and solvent‐induced damage to functional layers. Therefore, there is an urgent need for the optimization of the interconnecting layer (ICL) design in order to fabricate high‐performance solution‐processed tandem QLEDs. Here, by introducing a phosphomolybdic acid (PMA) layer between poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and poly(9‐vinylcarbazole) (PVK), an novel ICL, PVK/PMA/PEDOT:PSS/ZnO is proposed, with dual charge generation interfaces (CGIs): PVK/PMA and PEDOT:PSS/ZnO. The PMA interlayer serves not only smoothing the morphology of PEDOT:PSS to improve charge transport, but also forming a PVK/PMA CGI to enhance charge generation. Based on the excellent electrical and optical properties of the dual‐CGI ICL, the solution‐processed inverted tandem red QLEDs achieve an increased external quantum efficiency (EQE) of over three times compared to single‐junction devices. This provides a novel approach for the high‐efficiency solution‐processed tandem QLEDs, paving the way for the practical application of QLEDs.

Advances in display technology: augmented reality, virtual reality, quantum dot-based light-emitting diodes, and organic light-emitting diodes

Virtual reality, augmented reality, quantum dot light-emitting diodes, and organic light-emitting diodes have progressed over the last two years. Key achievements in these displays are discussed in terms of device performance.