Hongzhe Wang

Synthesis and assembly of monodisperse spherical Cu2S nanocrystals.

High-quality monodisperse Cu(2)S nanocrystals (sizes from 2 nm to 20 nm) have been successfully synthesized by the reaction of copper stearate (CuSt(2)) and dodecanethiol (DDT) in 1-octadecene (ODE). The nanocrystals were characterized using X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), and transmission electron microscopy (TEM). These as-prepared Cu(2)S nanocrystals with certain sizes have been found with good self-assembly behaviors, and they were easily to assemble into two-dimensional and three-dimensional superlattice structures. DDT served as both sulfur source and capping ligand, and was found a key factor to affect the growth and the self-assembly behaviors of the Cu(2)S nanocrystals.

Columnar Self-Assembly of Cu2S Hexagonal Nanoplates Induced by Tin(IV)−X Complex as Inorganic Surface Ligand

We have prepared columnar self-assembled Cu(2)S hexagonal nanoplates induced by a Sn-X complex for the first time and demonstrated that the Sn-X complex can affect not only the morphology of the nanocrystals but also the self-assembly ability of the nanocrystals.

Inorganic Sn–X complex ligands capped CuInS2 nanocrystals with high electron mobility

We report a facile method for the synthesis of size-controlled triangular CuInS2 (CIS) semiconductor nanocrystals (NCs) in the organic phase, and then, molecular metal chalcogenide complexes capped CIS NCs can be synthesized by exchanging original organic compounds with (NH4)4Sn2S6 inorganic ligands in environmentally benign solvent. The properties of CIS NCs (coated by both organic and inorganic ligands) were characterized by UV–Vis spectroscopy, fourier transform infrared, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and dynamic light scattering. CuInS2 NCs (before and after ligand exchange) films were spin coated on cleaned ITO glass substrates, and the charge transport properties were detected by current-voltage characteristic. We observed that the ligands on the surface of CIS NCs have been exchanged successfully, and the electrical transparency of (NH4)4Sn2S6-CIS NCs films was obviously increased than CIS NCs with organic capping ligands.

Highly Efficient Blue–Green Quantum Dot Light-Emitting Diodes Using Stable Low-Cadmium Quaternary-Alloy ZnCdSSe/ZnS Core/Shell Nanocrystals

High-quality blue-green emitting ZnxCd(1-x)S(1-y)Se(y)/ZnS core/shell quantum dots (QDs) have been synthesized by a phosphine-free method. The quantum yields of as-synthesized ZnxCd(1-x)S(1-y)Se(y)/ZnS core/shell QDs can reach 50-75% with emissions between 450 and 550 nm. The emissions of such core/shell QDs are not susceptible to ligand loss through the photostability test. Blue-green light-emitting diodes (LEDs) based on the low-cadmium ZnxCd(1-x)S(1-y)Se(y)/ZnS core/shell QDs have been successfully demonstrated. Composite films of poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) and ZnO nanoparticle layers were chosen as the hole-transporting and the electron-transporting layers, respectively. Highly bright blue-green QD-based light-emitting devices (QD-LEDs) showing maximum luminance up to 10000 cd/m(2), in particular, the blue QD-LEDs show an unprecedentedly high brightness over 4700 cd/m(2) and peak external quantum efficiency (EQE) of 0.8%, which is the highest value ever reported. These results signify a remarkable progress in QD-LEDs and offer a practicable platform for the realization of QD-based blue-green display and lighting.

Efficient and Bright Colloidal Quantum Dot Light-Emitting Diodes via Controlling the Shell Thickness of Quantum Dots

In this paper, we use a simple device architecture based on solution-processed ZnO nanoparticles (NPs) as the electron injection/transport layer and bilayer structure of poly(ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) as the hole injection/transport layer to assess the effect of shell thickness on the properties of quantum-dot-based light emitting diodes (QD-LEDs), comprising CdSe/CdS/ZnS core-shell QDs as the emitting layer. QDs with varying shell thickness were assessed to determine the best option of shell thickness, and the best improvement in device performance was observed when the shell thickness was 2.1 nm. Thereafter, different emissions of QDs, but with optimized same shell thickness (∼2.1 nm), were selected as emitters to be fabricated into same structured QD-LEDs. Highly bright orange-red and green QD-LEDs with peak luminances up to ∼30 000 and ∼52 000 cd m(-2), and power efficiencies of 16 and 19.7 lm W(-1), respectively, were demonstrated successfully. These results may demonstrate a striking basic prototype for the commercialization of QD-based displays and solid-state lightings.

Investigation on type-II Cu2S–CdS core/shell nanocrystals: synthesis and characterization

Type-II Cu2S–CdS core/shell (including Cu2S/CdS and CdS/Cu2S) semiconductor nanocrystals (NCs), which can produce efficient spatial separation of electrons and holes between the core and shell, were successfully synthesized. The results from absorption spectra, photoluminescence (PL) spectra, X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and PL lifetime measurements all confirmed the formation of the type-II core/shell NCs. The emission wavelength of the type-II Cu2S/CdS core/shell NCs can be readily tuned between 515 nm and 760 nm through two methods: core size control and shell thickness control. The highest PL quantum yield that the Cu2S/CdS core/shell NCs reached was ∼12% by controlling the shell thickness, while the core Cu2S nanocrystals had no PL at all. The PL decay data revealed that Cu2S/CdS NCs had a dual exponential characteristic and the PL emission with the longest lifetime (more than 1400 ns) occupied more than 85%. After overcoating ZnS, a Cu2S/CdS/ZnS core/shell1/shell2 structure was formed, which resulted in a blue-shift of the emission wavelength. Using the synthesis strategy of Cu2S/CdS, CdS/Cu2S type-II NCs also produced tunable emissions in the visible range.

Shape controlled synthesis of tadpole-like and heliotrope seed-like AgInS2 nanocrystals

A convenient synthesis strategy was developed to synthesize tadpole-like and heliotrope seed-like AgInS2 nanocrystals by thermolysis of sliver acetylacetonate (Agacac) and indium acetylacetonate [In(acac)3] in a high boiling point solvent. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), two-dimensional fast Fourier transform (2D-FFT), X-ray diffraction (XRD), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to investigate the factors of shape-controlled and the process of the phase transformation. In addition, it was found that the growth process of tadpole-like AgInS2 nanocrystals started with the formation of biphasic Ag-AgInS2 heterostructured nanocrystals and finally transformed into monophasic AgInS2 nanocrystals. These compositional, structural, and mechanistic findings provide valuable insight into the controlled solution growth of ternary chalcogenide nanocrystals and will aid in the development of solar cells using ternary I-III-VI2 semiconductors.

Size-, shape-, and assembly-controlled synthesis of Cu2−xSe nanocrystalsvia a non-injection phosphine-free colloidal method

In this paper, we report a facile, “green”, phosphine-free, low-cost, and non-injection method to obtain size-, shape-, and assembly-controllable Cu2−xSe nanocrystals which can be used as uniform building blocks. Different sizes of monodispersed Cu2−xSe nanocrystals were synthesized successfully by simply controlling the reaction temperature. The highly uniform Cu2−xSe nanocrystals can be well controlled from 4 to 20 nm when the temperature was set from 120 to 200 °C. By changing the ratios of CuSt2, oleic acid (OA), oleylamine (OAM), and selenium-octadecene (Se-ODE) precursor, Cu2−xSe nanocrystals with different shapes (hexagonal, elongated hexagonal bipyramid-shaped, trigonal pyramidal-shaped) and assembly behaviors (hexagonal Cu2−xSe nanodiscs with 1D, 2D, and 3D columnar self-assembly, elongated hexagonal bipyramid-shaped Cu2−xSe with 2D and 3D self-assembly, trigonal pyramidal-shaped Cu2−xSe nanocrystals with different arrays) were obtained indeed. Even though both OA and OAM were used as stabilizers to synthesize different shaped Cu2−xSe nanocrystals, FTIR results indicated that the surface of the as-synthesized nanocrystals was only capped by OAM. XRD studies confirmed that three different shapes of Cu2−xSe nanocrystals prepared with this non-injection method are all cubic berzelianite and well-crystallized. Current–voltage (I–V) behaviors of different shaped Cu2−xSe nanocrystals were measured and all found to have low resistivities.

Facile synthesis of high-quality CuInZnxS2+x core/shell nanocrystals and their application for detection of C-reactive protein

Highly photoluminescent (PL) CuInZnxS1+x nanocrystals (NCs) and CuInZnxS1+x/ZnS core/shell NCs were successfully synthesized by a facile colloidal method. First, a facile and reliable non-injection method for the synthesis of photoluminescent CuInZnxS2+x NCs was developed with inexpensive reagents. The relative PL quantum yields (QYs) of CuInZnxS2+x NCs could reach up to 30%, with tunable emissions in the range 580–780 nm. Then, CuInZnxS2+x/ZnS core/shell NCs were synthesized and showed greatly improved optical properties, the PL QY of the CuInZnxS2+x/ZnS NCs can reach up to 60%. Even in the near-infrared region, the PL QY still can achieve up to 45% due to the successful controlled red shift of PL during the ZnS shell growth process. More importantly, such core/shell NCs can be transferred into water successfully using amphiphilic oligomer (polymaleic acid n-hexadecanol ester) as a surface coating agent by an organic-aqueous phase transfer method and the PL QYs can be well controlled over 40%. Furthermore, a biosensor system (lateral flow immunoassays system, LFIA) for the detection of C-reactive protein (CRP) was developed by using this water-soluble CuInZnxS2+x/ZnS core/shell NCs as fluorescent label and a nitrocellulose filter membrane for lateral flow. The results showed that such CuInZnxS2+x/ZnS core/shell NCs were excellent fluorescent labels to detect CRP. The detection sensitivity for CRP could reach 1 ng mL−1.

Controlled synthesis of different types iron oxides nanocrystals in paraffin oil

Monodisperse Fe3O4 and FeO nanocrystals (NCs) with different sizes (from 10 nm to 50 nm) and different shapes (cube, sphere, and ellipsoid) were synthesized by simply adjusting reaction temperature or molar ratio of Fe/oleic acid (OA) during the decomposition of FeO(OH) in noncoordinating solvent. The concentration of OA affected the nucleation and growth of NCs by improving the chemical reaction driving force during the syntheses of different types of iron oxide NCs. It has been found that the reaction temperature influenced the reaction activity between FeO(OH) and OA. The structure of Fe oleate complexes was studied using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used for structural and chemical characterization of as-prepared iron oxide NCs.