Size, Shape-Dependent Growth of Semiconductor Heterostructures Mediated by Ag₂Se Nanocrystals as Seeds

Size- and shape-controllable Ag₂Se-ZnS nanorods (NRs) and nanowires (NWs) have been synthesized successfully by the solution–liquid–solid (SLS) method. By using Ag₂Se nanocrystals (NCs) as seeds and catalyst, colloidal Ag₂Se-ZnS NRs and NWs with controllable diameters and lengths in ranges of 5–12 nm and 15–600 nm were successfully synthesized by altering the experimental variables, such as diameter of Ag₂Se NCs, amount of precursor, reaction time, and reaction temperature. The Ag₂Se NCs not only played a key role in the control of the shape of ZnS NCs but also influenced the crystal structure of ZnS NCs. The related surface photovoltage of heterostructured Ag₂Se-ZnS NWs have also been studied and the formation of Ag₂Se-ZnS heterostructure was confirmed. Moreover, this SLS method was successfully exploited to synthesize Ag₂S-ZnS heterostructures

Morphology Evolution of Gradient-Alloyed Cd<i>_x</i>Zn_1–<i>x</i>Se<i>_y</i>S_1–<i>y</i>@ZnS Core–Shell Quantum Dots during Transmission Electron Microscopy Determination: A Route to Illustrate Strain Effects

In this work, we reported the morphology evolution (formation of voids & size reduction) of gradient-alloyed Cd<i>_x</i>Zn_1–<i>x</i>Se<i>_y</i>S_1–<i>y</i>@ZnS quantum dots under electron irradiation during transmission electron microscopy observation. By investigating the correlations between shell gradients and morphology evolution, the formation of voids can be explained by the continuous electron irradiation-induced atomic movement under interfacial strain. On the other hand, the size reduction can be attributed to the elastic scattering-enabled sputtering of surface atoms. The as-formed voids of Cd<i>_x</i>Zn_1–<i>x</i>Se<i>_y</i>S_1–<i>y</i>@ZnS quantum dots with CdS-rich cores are much larger than those of ZnSe-rich ones, and the sizes of voids decreased with the increasing of shell thickness. The comparison of the morphology evolution of Cd<i>_x</i>Zn_1–<i>x</i>Se<i>_y</i>S_1–<i>y</i>@ZnS core–shell quantum dots with different composition gradients demonstrated that the size and shape of as-formed voids illustrate the strain characteristics of shell gradient. This provides a guideline to understand the strain effects in gradient-alloyed core–shell quantum dots through transmission electron microscopy measurement. We believe the deep insights into gradient-alloyed Cd<i>_x</i>Zn_1–<i>x</i>Se<i>_y</i>S_1–<i>y</i>@ZnS core–shell quantum dots would push forward their optimization toward commercialized light-emitting technology

High-Efficiency, Low Turn-on Voltage Blue-Violet Quantum-Dot-Based Light-Emitting Diodes

We report high-efficiency blue-violet quantum-dot-based light-emitting diodes (QD-LEDs) by using high quantum yield ZnCdS/ZnS graded core–shell QDs with proper surface ligands. Replacing the oleic acid ligands on the as-synthesized QDs with shorter 1-octanethiol ligands is found to cause a 2-fold increase in the electron mobility within the QD film. Such a ligand exchange also results in an even greater increase in hole injection into the QD layer, thus improving the overall charge balance in the LEDs and yielding a 70% increase in quantum efficiency. Using 1-octanethiol capped QDs, we have obtained a maximum luminance (<i>L</i>) of 7600 cd/m² and a maximum external quantum efficiency (η_EQE) of (10.3 ± 0.9)% (with the highest at 12.2%) for QD-LEDs devices with an electroluminescence peak at 443 nm. Similar quantum efficiencies are also obtained for other blue/violet QD-LEDs with peak emission at 455 and 433 nm. To the best of our knowledge, this is the first report of blue QD-LEDs with η_EQE > 10%. Combined with the low turn-on voltage of ∼2.6 V, these blue-violet ZnCdS/ZnS QD-LEDs show great promise for use in next-generation full-color displays

Simultaneous Improvement of Efficiency and Lifetime of Quantum Dot Light-Emitting Diodes with a Bilayer Hole Injection Layer Consisting of PEDOT:PSS and Solution-Processed WO₃

Even though chemically stable metal oxides (MOs), as substitutes for poly­(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), have been successfully adopted for improving device stability in solution-processed quantum dot light-emitting diodes (QLEDs), the efficiencies of QLEDs are at a relatively low level. In this work, a novel architecture of QLEDs has been introduced, in which inorganic/organic bilayer hole injection layers (HILs) were delicately designed by inserting an amorphous WO₃ interlayer between PEDOT:PSS and the indium tin oxide anode. As a result, the efficiency and operational lifetime of QLEDs were improved simultaneously. The results show that the novel architecture QLEDs relative to conventional PEDOT:PSS-based QLEDs have an enhanced external quantum efficiency by a factor of 50%, increasing from 8.31 to 12.47%, meanwhile exhibit a relatively long operational lifetime (12 551 h) and high maximum brightness (>40 000 cd m^–2) resulting from a better pathway for hole injection with staircase energy-level alignment of the HILs and reduction of surface roughness. Our results demonstrate that the novel architecture QLEDs using bilayer MO/PEDOT:PSS HILs can achieve long operational lifetime without sacrificing efficiency

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% (λ_peak = 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 14,100 cd/m², current efficiency of 11.8 cd/A, and external quantum efficiency (EQE) of 16.2%. Importantly, the peak efficiency of the QLEDs with PMMA is achieved at ∼1,000 cd/m² and high EQE > 12% can be sustained in the range of 100 to 3,000 cd/m²

Hydroxyl-Terminated CuInS₂ Based Quantum Dots: Toward Efficient and Bright Light Emitting Diodes

CuInS₂ based quantum dots are emerging as low toxic materials for new generation white lighting technology due to their broad and color-tunable emissions as well as large Stokes shifts. Here, we developed a simple and <i>in situ</i> ligand exchange strategy for the fabrication of hydroxyl-terminated CuInS₂ based quantum dots capped with 6-mercaptohexanol. During the ligand exchange, long-chain methyl-terminated oleylamine on the quantum dots’ surface can be effectively and efficiently replaced by the short-chain hydroxyl-terminated 6-mercaptohexanol, enabling their solubility in polar organic solvents such as methanol, ethanol, and dimethylformamide. Moreover, the resulting hydroxyl-terminated quantum dots exhibit well-preserved photoluminescence properties with quantum yields of ∼70%. Using these hydroxyl-terminated CuInS₂ based quantum dots as an emitting layer, we fabricated efficient and bright light emitting diodes by adopting an inverted device structure. The optimized devices show a maximum luminance of 8,735 cd/m² and an external quantum efficiency of 3.22%. Furthermore, the performance enhancement can be explained by considering the decreased energy barriers between the electron transport layer and the emitting layer. The combination of high efficiency and enhanced brightness as well as the potential all-solution processability using green solvents makes hydroxyl-terminated quantum dots capped with 6-mercaptohexanol a new generation of materials for light emitting applications

Additional file 1: of Enhanced Performance of Quantum Dot-Based Light-Emitting Diodes with Gold Nanoparticle-Doped Hole Injection Layer

Details of synthesis of Zn1–xCdxSe/ZnS core/shell QDs, ZnO NPs, TEM images of different-sized Au NPs in water, AFM images of different-sized Au NP-doped PEDOT:PSS films, PL decay curves of ZnCdSe/ZnS core-shell QDs film, characteristics of devices as a function of thickness of QDs layer, SEM images of PEDOT:PSS films without and with different concentrations Au NPs (OD = 0.21, 22 nm) as well as various layers of device. This information is available free of charge via the Internet or from the author. (DOCX 3760 kb

Phosphine-Free Synthesis from 1D Pb(OH)Cl Nanowires to 0D and 1D PbSe Nanocrystals

In this paper, we report a new phosphine-free, low-cost, low-temperature colloidal method of controlled synthesis of PbSe nanocrystals in both zero-dimension (0D) and one-dimension (1D). Different from the widely used “hot injection” method and “nonprecursor injection” method, the novelty of this new method is that it does not require a nucleation process. Instead, high-quality presynthesized 1D Pb­(OH)Cl nanowires (∼80 to ∼160 nm in diameter) can be directly used as a Pb precursor and reacted with a Se precursor to form monodisperse dot-shaped 0D cubic PbSe and 1D orthorhombic PbSe nanowires. 0D cubic PbSe nanocrystals begin to form at elevated temperatures after the Se precursor is added to react with Pb­(OH)­Cl nanowires. By prolonging the reaction time for 3 h, good self-assembled 0D cubic PbSe nanocrystals can be synthesized with an average diameter of about 15 nm. Furthermore, such method has been demonstrated to synthsize high-quality 1D PbSe nanowires successfully with temperature as low as 110 °C. 1D PbSe nanowires possess a mean diameter of 15–24 nm with the shortest and longest length from 600 nm to 5 μm. The only sharp and strong peak, which is consistent with characteristic peaks of orthorhombic PbSe, indicates that the nanowires’ elongation axis is in the [111] direction, and 0D cubic PbSe nanocrystals change to 1D orthorhombic PbSe nanowires completely

MOESM1 of Highly sensitive and accurate detection of C-reactive protein by CdSe/ZnS quantum dot-based fluorescence-linked immunosorbent assay

Additional file 1. Additional figures

Synthesis and Evaluation of Ideal Core/Shell Quantum Dots with Precisely Controlled Shell Growth: Nonblinking, Single Photoluminescence Decay Channel, and Suppressed FRET

Due to the unique optical properties, colloidal quantum dots (QDs) are excellent candidates for developing next-generation display and solid-state lighting technologies. However, some factors including photoluminescence blinking and Förster resonance energy transfer (FRET) still affect their practical applications. Herein, a series of ZnCdSe-based core/shell QDs with low optical polydispersity have been successfully synthesized by a “low-temperature injection and high-temperature growth” precisely controlled method. The alloyed ZnCdSe core with a certain ratio of Cd and Zn was presynthesized first. Followed by accurate ZnS shell growth, the as-synthesized core/shell QDs are nonblinking with the nonblinking threshold volume of ∼137 nm³. The PL decay dynamics are all single-exponential for both QDs in solutions and close-packed solid films when ZnS shell thickness varying from 2 to 20 monolayers. FRET can be effectively suppressed after growing 10 monolayers of ZnS shell. All of these superb characteristics including nonblinking, single-exponential PL decay dynamics and suppressed FRET can be beneficial to high-quality QD-based light-emitting devices (QLEDs). By applying the ZnCdSe-based core/shell QDs with 10 monolayers ZnS shell, the highest external quantum efficiency of ∼17% was reached, which could compare favorably with the highest efficiency of green QLEDs with traditional multilayered structures