QD-based Light-emitting Diodes Research Articles

High‐Efficiency, Solution‐Processed White Quantum Dot Light‐Emitting Diodes with Serially Stacked Red/Green/Blue Units

AbstractDespite the fast advances in monochrome quantum dots (QDs) based light‐emitting diodes (QLEDs), the performance for white QLEDs (WQLEDs) with great potential for illumination and backlight applications to date has fallen short of that of state‐of‐the‐art white organic LEDs. Here, a highly efficient all‐solution‐processed WQLED with a serially stacked red/green/blue tandem structure, which displays an almost perfect white emission with the Commission Internationale de l'Enclairage coordinates of (0.34, 0.33) is reported. The white device exhibits peak current efficiency of 79.9 cd A−1 and external quantum efficiency of 28.0%, which are the highest efficiency values ever reported in WQLEDs. The record performance for the WQLEDs is achieved by the effective interconnecting layer with excellent charge generation and the insertion of a polyethylenimine ethoxylated interlayer between the ZnO electron transport layer and QDs emissive layer in each unit for better balancing charge injection and suppressing the quenching of QDs emission due to the contact with ZnO.

Room-Temperature Triple-Ligand Surface Engineering Synergistically Boosts Ink Stability, Recombination Dynamics, and Charge Injection toward EQE-11.6% Perovskite QLEDs.

Developing low-cost and high-quality quantum dots (QDs) or nanocrystals (NCs) and their corresponding efficient light-emitting diodes (LEDs) is crucial for the next-generation ultra-high-definition flexible displays. Here, there is a report on a room-temperature triple-ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide (TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid (OTAc) toward "ideal" perovskite QDs with a high photoluminescence quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel, stable ink characteristics, and effective charge injection and transportation in QD films, resulting in the highly efficient QD-based LEDs (QLEDs). Furthermore, the QD films with less nonradiative recombination centers exhibit improved PL properties with a PLQY of 61% through dopant engineering in A-site. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on CsPbBr3 QDs with the peak external quantum efficiency (EQE) of 11.6%, and the corresponding peak internal quantum efficiency (IQE) and power efficiency are 52.2% and 44.65 lm W-1 , respectively, which are the most-efficient perovskite QLEDs with colloidal CsPbBr3 QDs as emitters up to now. These results demonstrate that the as-obtained QD inks have a wide range application in future high-definition QD displays and high-quality lightings.

Highly Efficient All-Solution Processed Inverted Quantum Dots Based Light Emitting Diodes.

In all-solution processed inverted quantum dots based light emitting diodes (QLEDs), the solvent erosion on the quantum dot (QD) layer prevents devices from reaching high performance. By employing an orthogonal solvent 1,4-dioxane for the hole transport layer (HTL) poly(9-vinlycarbazole) (PVK), the external quantum efficiencies (EQE) of red QLED is increased 4-fold, while the luminous efficiencies (LE) of blue QLED is enhanced by 25 times, compared to the previous devices' record. To further improve the device efficiency and reduce the efficiency roll-off, solution processed PVK/poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] (TFB) double-layer HTL is introduced to facilitate hole injection with stepwise energy level. By reducing the hole injection barrier, the turn-on voltage of QLEDs decreases from 3.4 to 2.7 V for red, from 5.1 to 2.7 V for green, and from 5.3 to 4.1 V for blue. The peak LE reach 22.1 cd/A, 21.4 cd/A, and 1.99 cd/A, while the maximum EQE reach 12.7%, 5.29%, and 5.99%, for red, green, and blue QLEDs, respectively. To the best of our knowledge, the red and blue QLEDs exhibit the best device performance among all the all-solution processed inverted QLEDs. In addition, the blue QLED is the champion among all the inverted QLEDs, including the devices fabricated by thermal evaporation.

Nonblinking Quantum-Dot-Based Blue Light-Emitting Diodes with High Efficiency and a Balanced Charge-Injection Process

Blue nonblinking (>98% “on” time) ZnCdSe/ZnS//ZnS quantum dots (QDs) with absolute fluorescence quantum yield (QY) of 92% (λpeak = 472 nm) were synthesized via a low temperature nucleation and high temperature shell growth method. Such bright nonblinking ZnCdSe/ZnS//ZnS core/shell QDs exhibit not only good emission tunability in the blue-cyan range with corresponding wavelength from 450 to 495 nm but also high absolute photoluminescence (PL) QY and superior chemical and photochemical stability. Highly efficient blue quantum dot-based light-emitting diodes (QLEDs) have been demonstrated by using nonblinking ZnCdSe/ZnS//ZnS QDs as emissive layer, and the charge–injection balance within the QD active layer was improved by introducing a nonconductive layer of poly(methyl methacrylate) (PMMA) between the electron transport layer (ETL) and the QD layer, where the PMMA layer takes the role of coordinator to impede excessive electron flux. The best device exhibits outstanding features such as maximum luminance of...

Butterfly-inspired micro-concavity array film for color conversion efficiency improvement of quantum-dot-based light-emitting diodes.

Inspired by the Papilio blumei butterfly, quantum-dot (QD) film coupled with micro-concavity array (MCA) films is proposed in this Letter to enhance color conversion efficiency (CCE) of QD-based light-emitting diodes (LEDs). The diameter, aspect ratio, and pitch of the MCA are optimized in the optical simulations. Both the simulation and experimental results show that the scattering and double reflection effects are the key to the CCE improvement of QD films. The results show that the CCEs are increased from 19.98% to 21.59% and 21.78% (350mA) for single-sided microstructured QD film and double-sided microstructured QD film configurations, respectively. Overall, the MCA film is a promising solution to enhance the CCE of QD-based LEDs.

High‐Efficiency and Stable Quantum Dot Light‐Emitting Diodes Enabled by a Solution‐Processed Metal‐Doped Nickel Oxide Hole Injection Interfacial Layer

AbstractStabilization is one critical issue that needs to be improved for future application of colloidal quantum dot (QD)‐based light‐emitting diodes (QLEDs). This study reports highly efficient and stable QLEDs based on solution‐processsed, metal‐doped nickel oxide films as hole injection layer (HIL). Several kinds of metal dopants (Li, Mg, and Cu) are introduced to improve the hole injection capability of NiO films. The resulting device with Cu:NiO HIL exhibits superior performance compared to the state‐of‐the‐art poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) (PEDOT:PSS)‐based QLEDs, with a maximum current efficiency and external quantum efficiency of 45.7 cd A−1 and 10.5%, respectively. These are the highest values reported so far for QLEDs with PEDOT:PSS‐free normal structure. Meanwhile, the resulting QLED shows a half‐life time of 87 h at an initial luminance of 5000 cd m−2, almost fourfold longer than that of the PEDOT:PSS‐based device.

The Effect of Electron and Hole Transfer Layers on the Electro-Optical Properties of Solution-Processed QD-LED

Colloidal quantum-dots-based light emitting diodes (QD-LEDs) have been considered attractive display devices because of the remarkable electrical/optical characteristics of colloidal quantum dots. QD-LEDs have attracted particular interest not only because of their wide-range color tunability, high brightness and good color purity by the narrow emission bandwidth, but also because of their printability with a large size under atmospheric pressure.Nevertheless, achieving optimal control of charge transport/light emission and forming the necessary multilayer device structures is still a major challenge. The hole transport layer (HTL) and electron transport layer (ETL) thickness should be optimized to confine the electron and holes to the recombination zone in an emitting material layer (EML), i.e., the QD layer. For all-solution-processed QD-LEDs, inorganic and organic layers as the ETL and HTL were employed and optimized to achieve improved electroluminescence performances. Red QDs in the core/shell/shell type multi-structure, ZnO nanoparticles, and TiO2 were synthesized using the procedures reported elsewhere. The QD-LEDs were fabricated on patterned ITO glass. As a hole transfer layer, a PEDOT:PSS solution was spin coated. The organic hole transport layer, PVK, was coated on the PEDOT:PSS layer at a different rates to obtain a range of thicknesses. The CdSe/CdS/ZnS QDs (20 mg/mL) were spin coated. On the QD layers, various concentrations of ZnO NPs or TiO2 layers were spin-coated. Finally, 100 nm aluminum, as a cathode layer, was deposited on the ZnO NPs layer by vacuum evaporation As electron charge transport layers and hole charge transport layer, zinc oxide nanoparticles and polyvinyl carvazole (PVK) were applied to all solution-processed quantum dot light emitting diodes. The quantum dot as the emitting layer, and the zinc oxide nanoparticles and titanium oxide, as the carrier transporting layers were synthesized using a solution mediated process. The optimized device using 45 nm zinc oxide nanoparticles as the electron transport layer and 18 nm PVK as the hole transport layer showed a lower turn-on voltage and better luminescence, resulting in a luminance of 13,730 cd/m2, current efficiency of 3.27 cd/A, and EQE of 2.67%.

Quantum dot white light emitting diodes with high scotopic/photopic ratios.

Alloy core/shell CdxZn1-xS/ZnS quantum dots (QDs) are emerging as robust candidates for light-emitting diodes (LEDs), however the emission range of the current CdxZn1-xS/ZnS is quite limited, ranging from 390 to 470 nm. It still remains a challenging task to construct white LEDs based on current CdxZn1-xS/ZnS system. Here, a versatile ZnSe with a moderate band gap is introduced onto the Cd0.1Zn0.9S core. The ZnSe shell, on one hand, can passivate the core surface which leads to bright emissions. On the other hand, it is essential in extending the emission to red region so that the emission wavelengths of Cd0.1Zn0.9S/ZnS and Cd0.1Zn0.9S/ZnSe QDs can cover the whole visible region, which is very important for white LED applications. Two- and four-hump QD-based LEDs are computationally and experimentally investigated. Results show that four-hump quantum dot light-emitting diodes (QLED) have better performances than the two-hump one, in the luminous and the vision properties. The fabricated white LEDs (WLEDs) based on Cd0.1Zn0.9S/ZnS and Cd0.1Zn0.9S/ZnSe QDs exhibits a scotopic/photopic ratio (S/P) ratio as high as 2.52, which exceeds the current limit of 2.50 by common lighting technologies, a color rendering index of 90.3, a luminous efficacy of optical radiation of 460.78 lumen per unit optical power, and a correlated color temperature of 5454 K. These results suggest that CdxZn1-xS/ZnS and CdxZn1-xS/ZnSe quantum dots serving as emitters hold great promise for the next-generation white light source with better S/P ratio.

Spectral optimization of color temperature tunable white LEDs based on perovskite quantum dots for ultrahigh color rendition

The spectral optimization for maximizing limited luminous efficacy (LLE) of correlated color temperature (CCT) tunable white light-emitting diodes (LEDs) with two, three and four color perovskite quantum dots (QDs) excited by a blue chip was investigated under the constraint of designated ultrahigh color rendering index (CRI) and color quality scale (CQS). The results show that high quality white lights with CRIs of 96-97, CQSs of 95-96, and LLEs of 243-225 lm/W at CCTs of 2700 K to 6500 K could be realized by the QDs-converted white LEDs (QD-WLEDs) using a blue chip and different combinations of perovskite quantum dots. The luminous efficacies of QD-WLEDs are expected to reach 114 to 122 lm/W at CCTs of 2700 K to 6500 K, if the radiant efficiency of a blue chip is 60% and the real PLQY values of perovskite QDs are 75%. These results demonstrate that perovskite QD-based LEDs are expected to be promising in next generation display and lighting technologies.

Carrier transport and emission efficiency in InGaN quantum-dot based light-emitting diodes

We present a study of blue III-nitride light-emitting diodes (LEDs) with multiple quantum well (MQW) and quantum dot (QD) active regions (ARs), comparing experimental and theoretical results. The LED samples were grown by metalorganic vapor phase epitaxy, utilizing growth interruption in the hydrogen/nitrogen atmosphere and variable reactor pressure to control the AR microstructure. Realistic configuration of the QD AR implied in simulations was directly extracted from HRTEM characterization of the grown QD-based structures. Multi-scale 2D simulations of the carrier transport inside the multiple QD AR have revealed a non-trivial pathway for carrier injection into the dots. Electrons and holes are found to penetrate deep into the multi-layer AR through the gaps between individual QDs and get into the dots via their side edges rather than via top and bottom interfaces. This enables a more homogeneous carrier distribution among the dots situated in different layers than among the laterally uniform quantum well (QWs) in the MQW AR. As a result, a lower turn-on voltage is predicted for QD-based LEDs, as compared to MQW ones. Simulations did not show any remarkable difference in the efficiencies of the MQW and QD-based LEDs, if the same recombination coefficients are utilized, i.e. a similar crystal quality of both types of LED structures is assumed. Measurements of the current–voltage characteristics of LEDs with both kinds of the AR have shown their close similarity, in contrast to theoretical predictions. This implies the conventional assumption of laterally uniform QWs not to be likely an adequate approximation for the carrier transport in MQW LED structures. Optical characterization of MQW and QD-based LEDs has demonstrated that the later ones exhibit a higher efficiency, which could be attributed to better crystal quality of the grown QD-based structures. The difference in the crystal quality explains the recently observed correlation between the growth pressure of LED structures and their efficiency and should be taken into account while further comparing performances of MQW and QD-based LEDs. In contrast to experimental results, our simulations did not reveal any advantages of using QD-based ARs over the MQW ones, if the same recombination constants are assumed for both cases. This fact demonstrates importance of accounting for growth-dependent factors, like crystal quality, which may limit the device performance. Nevertheless, a more uniform carrier injection into multi-layer QD ARs predicted by modeling may serve as the basis for further improvement of LED efficiency by lowering carrier density in individual QDs and, hence, suppressing the Auger recombination losses.

Al-doped ZnS shell as a surface shield for enhancing the stability of Cu:ZnInS/ZnS/ZnS:Al quantum dots and their application in light emitting diodes

Cu:ZnInS/ZnS/ZnS:Al quantum dots (QDs) with a Cu-doped inner core and an Al-doped outer shell were synthesized in this work, exhibiting improved stability of luminescence, compared with Cu:ZnInS/ZnS/ZnS QDs. The X-ray diffraction patterns and photoluminescence spectra confirmed that the Al ions were doped into the ZnS shell. The stability of Cu:ZnInS/ZnS/ZnS:Al QDs under various thermal annealing temperatures was studied by steady-state and time resolved photoluminescence spectroscopy. The Cu:ZnInS/ZnS/ZnS:Al QDs had a relatively small reduction of 20% in photoluminescence lifetime from 167ns under thermal annealing at 50°C to 132.8ns at 250°C, compared to a 55% drop for the undoped ones, indicating less thermal effect on the photoluminescence of the QDs with an Al-doped shell. The Cu:ZnInS/ZnS/ZnS:Al QD-based light emitting diodes (LEDs) had a 3% luminescence enhancement under injection current of 10mA for 30h, compared to a 13% reduction for the undoped QDs, suggesting improved thermal stability of photoluminescence for the QDs with Al-doped shell. Finally, Cu:ZnInS/ZnS/ZnS:Al QD-based white LEDs with good color rendering index (>80) and correlated color temperature (<4500K) were fabricated by combining with green emitting CuInS2/ZnS QDs. The self-passivated QDs show promises for enhancing thermal stability of QD-based LEDs in the conserved energy lighting industry.

Enhancing the thermal dissipation of a light-converting composite for quantum dot-based white light-emitting diodes through electrospinning nanofibers

Quantum dots (QDs) have been developed as one of the most promising light-converting materials for white light-emitting diodes (LEDs). In current QD-based LED packaging structures, composites of QDs and polymers are used as light-converting layers. However, the ultralow thermal conductivity of such composites seriously hinders the dissipation of QD-generating heat. In this paper, we demonstrate a method to enhance the thermal dissipation of QD-polymer composites through electrospinning polymer nanofibers. QD-polymer films embedded by electrospun nanofibers were prepared. Benefitting from aligned polymer chains in the electrospun nanofibers, the through-panel and in-panel thermal conductivities of the proposed QD-polymer film increased by 39.9% and 423.1%, respectively, compared to traditional QD-polymer film. The proposed and traditional QD-polymer films were both packaged on chip on board (CoB) LEDs for experimental comparison. Compared to traditional QD-polymer film, the luminous flux and luminous efficiency of the LEDs were increased by up to 51.8% and 42.9% by the proposed QD-polymer film under a current of 800 mA, respectively. With an increase in the driving current from 20–800 mA, the correlated color temperature (CCT) variation decreased by 72.7%. The maximum temperatures in the QD-polymer films were reduced from 419 K–411 K under a driving current of 200 mA.

Pure Blue and Highly Luminescent Quantum‐Dot Light‐Emitting Diodes with Enhanced Electron Injection and Exciton Confinement via Partially Oxidized Aluminum Cathode

The balance injection of holes and electrons into a thin emissive quantum dot (QD) layer for efficient radiative recombination is critical to the color purity, stability, and efficiency of the QD‐based light‐emitting diodes (QD‐LEDs). Due to the difficulty of charge injection into wide band gap blue QD layer, the performance of blue QD‐LED is obviously inferior to the green and red counterparts. Here, high‐performance ZnCdS/ZnS graded core/shell‐based blue QD‐LEDs with partial oxidized aluminum cathode (Al:Al2O3) via simple autoxidation are demonstrated. There is no any additional electron transport layer/hole transport layer involved in the device, which guarantees the color purity and simplifies the fabrication processes. Furthermore, the Al:Al2O3 cathode greatly enhances the charge injection and exciton recombination, rendering significant improvement in luminance and current efficiency compared with the control devices with Al or Alq3/Al electrodes. A record luminance of over 13 000 cd m−2 has been achieved for blue QD‐LEDs with Al:Al2O3 cathode. The findings of this study indicate that this simply processed and easily controlled autoxidation procedure is a promising strategy to achieve high‐performance blue QD‐LEDs.

Colloidal quantum-dots surface and device structure engineering for high-performance light-emitting diodes

Abstract The application of colloidal quantum dots for light-emitting devices has attracted considerable attention in recent years, due to their unique optical properties such as size-dependent emission wavelength, sharp emission peak and high luminescent quantum yield. Tremendous efforts have been made to explore quantum dots for light-emission applications such as light-emitting diodes (LEDs) and light converters. The performance of quantum-dots-based light-emitting diodes (QD-LEDs) has been increasing rapidly in recent decades as the development of quantum-dots synthesis, surface-ligand engineering and device-architecture optimization. Recently, the external quantum efficiencies of red quantum-dots LEDs have exceeded 20.5% with good stability and narrow emission peak. In this review, we summarize the recent advances in QD-LEDs, focusing on quantum-dot surface engineering and device-architecture optimization.

Solution-processed inorganic copper(i) thiocyanate as a hole injection layer for high-performance quantum dot-based light-emitting diodes

The introduction of CuSCN as the hole injection material significantly improved the turn-on voltage of quantum dot-based LEDs.

Enhanced Performance of Quantum Dot-Based Light-Emitting Diodes with Gold Nanoparticle-Doped Hole Injection Layer.

In this paper, the performance of quantum dot-based light-emitting diodes (QLEDs) comprising ZnCdSe/ZnS core-shell QDs as an emitting layer were enhanced by employing Au-doped poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) hole injection layer (HIL). By varying the concentration and dimension of Au nanoparticle (NP) dopants in PEDOT:PSS, the optimal devices were obtained with ~22-nm-sized Au NP dopant at the concentration with an optical density (OD) of 0.21. Highly bright green QLEDs with a maximum external quantum efficiency (EQE) of 8.2 % and a current efficiency of 29.1 cd/A exhibit 80 % improvement compared with devices without Au NP dopants. The improved performance may be attributed to the significant increase in the hole injection rate as a result of the introduction of Au NPs and the good matching between the resonance frequency of the localized surface plasmon resonance (LSPR) generated by the Au NPs and the emission band of QD layer, as well as the suppressed Auger recombination of QD layer due to the LSPR-induced near-field enhanced radiative recombination rate of excitons. These results are helpful for fabricating high-performance QD-based applications, such as full-color displays and solid-state lighting.Graphical 80 % enhancement of efficency of quantum dot-based light-emitting diodes with gold nanoparticle doped hole-injection-layer.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1573-8) contains supplementary material, which is available to authorized users.

High-performance azure blue quantum dot light-emitting diodes via doping PVK in emitting layer

Highly bright and efficient azure blue quantum dot-based light-emitting diodes (QD-LEDs) have been demonstrated by employing ZnCdSe core/multishell QDs as emitters and the crucial development we report here is the ability to dramatically enhance the efficiency and brightness through doping poly vinyl(N-carbazole) (PVK) in the emissive layer to balance the charge injection. The best device displays remarkable features like maximum luminance of 13,800 cd/m2, luminous efficiency of 6.41 cd/A, and external quantum efficiency (EQE) of 8.76%, without detectable red-shift and broadening in electroluminescence (EL) spectra with increasing voltage as well as good spectral matching between photoluminescence (PL) and EL. Such azure blue quantum-dot LEDs show a 140% increase in external quantum efficiency compared with QD-LEDs without PVK. More important, the peak efficiency of the QD-LEDs with PVK dopant is achieved at luminance of about 1000 cd/m2, and high efficiency (EQE>8%) can be maintained with brightness ranging from 200 to 2400 cd/m2. There are two main aspects of the role of PVK in the proposed system. Firstly, the lower HOMO of PVK than (poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) can reduce the potential barrier for 0.4 eV at the interface of QDs and hole transport layer which could result in higher hole injection efficiency along with good EQE as compared to TFB-only HTLs. Secondly, with PVK acting as buffer layer of TFB and QDs, the exciton energy transfer from the organic host to the QDs can be effectively improved.

The Role of Emission Layer Morphology on the Enhanced Performance of Light‐Emitting Diodes Based on Quantum Dot‐Semiconducting Polymer Hybrids

The influence of the morphology of quantum dot (QD)‐semiconducting polymer hybrid emission layers on the performance of quantum dot‐based light emitting diodes (QLEDs) is systematically investigated. Chemically grafted QD‐semiconducting polymer hybrids are fabricated by the ligand exchange procedure between CdSe/CdxZn1−xS QDs and a new block copolymer consisting of a carbazole‐based electroactive block with a low highest occupied molecular orbital level and a disulfide‐based anchor block. The performance of QLEDs with hybrid emission layers is compared with QLEDs utilizing QD‐only and physically mixed QD/polymer emission layers. It is shown that only in the emission layers formed by chemically grafted hybrids QDs are evenly distributed throughout the semiconducting polymer matrix. This leads to improved charge transport balance and suppressed photoluminescence quenching of QDs. As a result, hybrid QLEDs with the peak external quantum efficiency of 5.6% and the peak luminance of 21 707 cd m−2 which outperform the conventional devices with QD‐only emission layers are fabricated.

Influence of Ambient Gas on the Performance of Quantum-Dot Light-Emitting Diodes.

Here, we report the influence of the ambient gas on the performance of quantum dot-based light-emitting diodes (QD-LEDs). The blue QD-LED devices with the maximum external quantum efficiency of 8.1% and the turn-on voltage of 2.7 V could be obtained in air. The efficiency decreases by 12% and turn-on voltage increases by 0.3 V relative to the control devices fabricated in a N2-filled glovebox. The histogram of maximum external quantum efficiency (EQE) shows average peak EQE of 8.08% and a low standard deviation of 3.63%, suggesting high reproducibility. Correspondingly, the operational lifetime of 376 h is obtained, which is on par with 408 h of devices fabricated in N2. For the devices fabricated in air, relatively high efficiency could be maintained only at low voltages, because of the near balanced injection of carriers under low bias. The measurements of contact potential difference, chemical composition, and surface roughness are used to verify the variation of energy level and surface morphology of films influenced by different ambient gas. These results would offer reasonable guidance for the application of QD-LEDs in actual large-scale production.

Light-Emitting Diodes Based on All-Quantum-Dot Multilayer Films and the Influence of Various Hole-Transporting Layers on the Performance**Supported by the National High Technology Research and Development Program of China under Grant No 2013AA032205, the National Natural Science Foundation of China under Grant Nos 11474018, 51272022 and 61575019, the Specialized Research Fund for the Doctoral Program of Higher Education of China under

We present a systematic analysis of the exciton-recombination zone within all-quantum-dot (QD) multilayer films using sensing QD layers in QD-based light-emitting diodes (QLEDs), and demonstrate the all-QD multilayer films with different sequences of layers prepared by inserting a sensing blue QD layer denoted as B at various positions within four red QD multilayers denoted as R. We also use different hole transporting layers (PVK, CBP as well as poly-TPD) to prevent the formation of leakage current and to improve the luminance. The results show that the total EL emission is mostly at the fourth (60%) and fifth (40%) QD monolayers, adjacent to ITO. This presents both decreasing current density and increasing brightness with different hole transporting layers, thus resulting in more efficient performance.