CdS CdSe Research Articles

Surface Defect-Driven Chemical Transformation of MoSe2 Nanosheets

The chemistry of atomically thin two-dimensional layered transition metal dichalcogenides (TMDs) largely depends upon the presence of defect sites in their structures. Here, we demonstrate the role of defects of MoSe2 nanosheets (NSs) in two different transformative reactions for the synthesis of MoSe2–CdS nano-heterostructures (NHSs) and CdSe quantum dots (QDs). MoSe2–CdS NHSs are synthesized via passivating the defects of MoSe2 using thiol moieties, followed by the growth of CdS over the surface of MoSe2 NSs. Furthermore, in the absence of thiols, we observe that defects in MoSe2 NSs significantly accelerate the cation-exchange process upon direct exposure to the cadmium (Cd) precursor, resulting in the formation of CdSe QDs through cation displacement reaction (CDR). We have probed the transformation of MoSe2 NSs into CdSe QDs through Raman and optical spectroscopic measurements. Furthermore, theoretical calculations under the framework of density functional theory (DFT) suggest that CDR is feasible on the surface of defect-rich NSs, which becomes unfavorable in the case of defect-free or thiol-passivated MoSe2 NSs. These results provide new insights into understanding the multifaceted role of defects of TMDs in different transformative reactions.

Ternary compound heterojunction from isomerism h-CdS/c-CdSe exhibits boosting photoelectrochemical and hydrogen evolution reaction properties

A novel h-CdS/c-CdSe ternary compound heterojunction catalyst CdSS is constructed from isomerism hexagonal CdS and cubic CdSe. The isomerism hexagonal CdS and cubic CdSe is the key factor to obtain the CdSS heterojunction, as compared, ternary compound CdSSe can only be prepared from isomorphic hexagonal CdS and hexagonal CdSe. Under different S:Se ratio, the main XRD peaks of CdSS displayed continuous shift between related CdS and CdSe peaks that confirms the S and Se atoms embedding CdSe and CdS lattice respectively to form atomic level ternary compound heterojunction. The photoelectrochemical and electrocatalytic results show that the CdSS catalysts have boosting properties. Under an optimal S:Se ratio, the photocurrent density of the CdSS reach 8.23 μA/cm2, which was 4.5 times that of original CdS (1.83 μA/cm2), 4.9 times of CdSe (1.67 μA/cm2) and 5.1 times of CdSSe (1.60 μA/cm2). The hydrogen evolution reaction Tafel slope of CdSS also declined 60% compared with CdS and 64% compared with CdSe. The electrocatalytic impedance and fluorescence spectra fully show that CdSS has lower internal resistance and low electron-hole recombination efficiency due to the atomic level heterojunction. The work develops a new strategy to construct high efficiency atomic level ternary compound heterojunction between isomerism homologous element compounds.

Reasoning the Photoluminescence Blinking in CdSe–CdS Heteronanostructures as Stacking Fault-Based Trap States

Reasoning the Photoluminescence Blinking in CdSe–CdS Heteronanostructures as Stacking Fault-Based Trap States

Engineering the synthesized colloidal CuInS2 passivation layer in interface modification for CdS/CdSe quantum dot solar cells.

Interface modification is an important means to enhance the photovoltaic performance of quantum dot sensitized solar cells (QDSCs). The TiO2/CdS/CdSe solar cells are sensitized with CdS QDs and CdSe QDs, which inevitably introduces a new interface to form a recombination center. Therefore, it is necessary to coat a passivation layer in order to effectively inhibit charge recombination at the CdS/CdSe interface. In this work, CuInS2 (CIS) has been introduced into the CdS/CdSe QD system as an inner passivation layer and the CdS/CIS/CdSe photoanode structure has been fabricated in an environmentally friendly manner. The extracted charge amount (Q) is used to express the charge separation efficiency, indicating that we have obtained outstanding charge extraction efficiency in CIS based CdS/CdSe QDSCs. As a result, the photocurrent density of the TiO2/CdS/CIS/CdSe photoanode significantly has increased from 19.01 mA cm-2 to 22.74 mA cm-2 (TiO2/CdS/CdSe photoanode), which demonstrates a higher photoconversion efficiency of 4.52% in comparison with that of TiO2/CdS/CdSe photoanode.

CdS@CdSe Core/Shell Quantum Dots for Highly Improved Self-Powered Photodetection Performance.

Uniform, well-defined cadmium sulfide@cadmium selenide core/shell quantum dots (CdS@CdSe QDs) were, for the first time, successfully synthesized by a solvothermal method and chemical bath growth for photoelectrochemical activities. The as-synthesized CdS@CdSe QDs not only exhibit superior self-powered photoresponse behavior and excellent stability under ambient conditions but also display significantly improved current densities and photoresponsivity compared to those of individual CdS QDs or CdSe QDs, mainly due to the built-in electric field, and thus have great potential in the fields of renewable energy and renewable energy consumption for carbon neutrality target achievement.

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Selective Excitation of CdSe/CdS Dot‐in‐Rod Nanocrystals and Distinct Roles of Electrons and Holes in Photophysical and Photochemical Interactions with Ambient Air

CdSe/CdS dot‐in‐rod (DiR) nanocrystals are an advantageous heterostructured semiconductor system with a quasi‐type‐II electronic band structure, which enables a rich diversity of optical manipulation of carrier excitations and interactions. Herein, the selective excitation of respective CdSe quantum dots (QDs) and CdS nanorods of the CdSe/CdS DiR nanostructure is reported, which results in the distinct presence of different types of carriers at the nanorod surface. The presence of only electrons at the surface upon CdSe QD excitation leads to photophysical interactions with ambient air, which is manifested as reversible photoluminescence (PL) of the CdSe QDs. The excitation of CdS nanorods produces holes at the surface, which induces photooxidation of the CdS surface and irreversible change in PL intensity and spectral lineshape. Benefitting from unambiguously relating carrier types to photophysical and photochemical interactions, this research also verifies that trap states at the CdS surface do not act as nonradiative recombination centers, which can be removed by photochemical reactions. Herein, distinct roles of electrons and holes in the photophysical and photochemical interactions with ambient air are identified, and a more precise understanding of the interacting mechanisms is achieved.

Organic polymer and perovskite CdSe–CdS QDs hybrid thin film: a new model for the direct detection of light elements

A window-less X-ray detector fabrication is a challenging job for physicists and technologists. Using a high atomic number (Z) nano-particles (NPs), such as CdSe–CdS quantum dots (QDs) in nano-form, are the most versatile nano-particles and the most suitable choice for energy-dispersive X-ray spectroscopy analysis of light elements. There is no report on the fabrication of a windowless X-ray detector by using core–shell CdSe–CdS QDs, so far as we know. We have observed the luminescence properties of CdSe/CdS core–shell QDs–cellulose hybrid thin films and characterized them. The blaze union of high photoluminescence (PL) of CdSe/CdS core–shell QDs was synthesized by a high-temperature short-time handling approach with a quantum yield of 70%. The surface, configurationally characterizations, and optical characteristics of the above thin films were examined utilizing X-ray diffraction, transmission electron microscopy, PL, scanning electron microscopy, and I–V trademark strategies. This experimental work confirmed thin films coated with QDs of core–shell CdSe–CdS which improve the PL capability of nano-crystalline cellulose. The distribution of a quantum size possesses a rigid structure in the total growth process of the entire shell during the experiment, which is indicated in the absorption spectra followed by a sharp PL peak at 630 nm. It is expected that the present study will have a good promise for X-ray-sensing applications.

CdS/CdSe HETEROSTRUCTURES GROWN BY CHEMICAL TECHNIQUES ON FLEXIBLE PET/ITO SUBSTRATES

Undoped and Mn-doped CdS films, CdSe films and CdS:Mn/CdSe heterostructures were deposited by chemical techniques. Undoped and Mn-doped CdS films were grown onto flexible PET/ITO substrates by chemical bath deposition at different temperatures. CdSe thin films were synthesized following a two stages process. In the first stage, CdO2 precursor films, were synthesized by chemical bath deposition at different deposition time. In the second stage, the CdO2 precursor films were transformed into CdSe films by immersion in a Se ionic solution. CdS, CdS:Mn, CdSe and CdS/CdSe samples were characterized by high-resolution transmission electron microscopy, UV-vis, Raman and room temperature photoluminescence spectroscopies. The structural characterization indicates that CdS and CdSe films with hexagonal phase were obtained. CdSe films showed the LO Raman mode with three order phonon replicas, an indication of the excellent crystalline quality of the samples.

Emerging nanoscience with discotic liquid crystals

Discotic liquid crystals (DLCs) are one-dimensional organic semiconducting materials and represent new low cost, rejuvenating materials in optoelectronics. The development of novel supramolecular materials based on liquid crystals (LCs) hybridized with various metallic, semiconducting, and carbon-based materials with optimized functionalities on the nanometer scale attracted much attention in liquid crystal nanoscience. The ability to combine supramolecular liquid crystalline chemistry with nanoscience is very attractive for several reasons. This review focuses on our recent advances in discotic liquid crystal nanoscience. Driven by the self-assembly of both liquid crystals and nanostructures, LC–nanomaterial nanocomposites (LC–NCs) are spontaneously formed through molecular self-organization at the nanometer scale. The careful design of different LC–NCs through enhanced LC properties opened a new era for organic electronics. A brief introduction to LCs is presented with emphasis on DLCs, which is followed by recent developments in the self-assembly of various nanostructures in discotics. We focus on how nanostructures can be self-assembled in such supramolecular materials so that self-organizing functional systems of discotics can be created with tuned physical properties, such as the thermal stability, optoelectronic and dielectric parameters, and response time, in LCs. We conclude this review by discussing the further development of nanoscience with LCs and applications in organic electronics. Our recent studies on how nanostructures can be self-assembled in discotic liquid crystals to create self-organizing functional systems of discotics with tuned physical properties are reviewed. In the first part of the article, charge carrier and semiconducting properties of discotic liquid crystals in the form of 1-D molecular wires are described. The second part of this report summarized our recent results on self-assembly of Ag, Au, Cu, and graphene nanoparticles, carbon dots, CdTe and CdSe quantum dots, gold nanorods, CdS nanoribbons, silver nanodisks, and graphene sheets in discotics.

Superhigh flexibility and out-of-plane piezoelectricity together with strong anharmonic phonon scattering induced extremely low lattice thermal conductivity in hexagonal buckled CdX (X = S, Se) monolayers

Although CdX (X = S, Se) has been mostly studied in the field of photocatalysis, photovoltaics, their intrinsic properties, such as, mechanical, piezoelectric, electron and phonon transport properties have been completely overlooked in buckled CdX monolayers. Ultra-low lattice thermal conductivity [1.08 W m−1 K−1 (0.75 W m−1 K−1)] and high p-type Seebeck coefficient [1300 μV K−1 (850 μV K−1)] in CdS (CdSe) monolayers have been found in this work based on first-principles DFT coupled to semi-classical Boltzmann transport equations, combining both the electronic and phononic transport. The dimensionless thermoelectric figure of merit is calculated to be 0.78 (0.5) in CdS (CdSe) monolayers at room temperature, which is comparable to that of two-dimensional (2D) tellurene (0.8), arsenene and antimonene (0.8), indicating its great potential for applications in 2D thermoelectrics. Such a low lattice thermal conductivity arise from the participation of both acoustic [91.98% (89.22%)] and optical modes [8.02% (10.78%)] together with low Debye temperature [254 K (187 K)], low group velocity [4 km s−1 (3 km s−1)] in CdS (CdSe) monolayers, high anharmonicity and short phonon lifetime. Substantial cohesive energy (∼4–5 eV), dynamical and mechanical stability of the monolayers substantiate the feasibility in synthesizing the single layers in experiments. The inversion symmetry broken along the z direction causes out-of-plane piezoelectricity. |d33| ∼ 21.6 pm V−1, calculated in CdS monolayer is found to be the highest amongst structures having atomic-layer thickness. Superlow Young’s modulus ∼41 N m−1 (31 N m−1) in CdS (CdSe) monolayers, which is comparable to that of planar CdS (29 N m−1) and TcTe2 (34 N m−1), is an indicator of its superhigh flexibility. Direct semiconducting band gap, high carrier mobility (∼500 cm2 V−1 s−1) and superhigh flexibility in CdX monolayers signify its gigantic potential for applications in ultrathin, stretchable and flexible nanoelectronics. The all-round properties can be synergistically combined together in futuristic applications in nano-piezotronics as well.

Experimental Evidence for Two-Dimensional Ostwald Ripening in Semiconductor Nanoplatelets

Colloidal semiconductor nanoplatelets are rectangular, quasi-two-dimensional crystallites that are only a few atomic layers thick. In the most heavily studied systems (such as CdE with E = S, Se, or Te), the highly anisotropic nanoplatelet shape forms from an isotropic cubic crystal lattice. This has been difficult to reconcile with standard nanocrystal growth models. Previously, we proposed that nanoplatelets arise due to an intrinsic kinetic instability that enhances growth on narrow crystal facets under surface-reaction-limited conditions. Here, we test this model experimentally by synthesizing small “baby” CdS nanoplatelets and performing ripening experiments. During heating, we observe transitions to thicker nanoplatelet populations that are consistent with two-dimensional Ostwald ripening. We then heat CdSe nanoplatelets in the presence of “baby” CdS nanoplatelets to form CdSe–CdS core–crown nanoplatelets. This indicates that individual nanoplatelets dissolve and transfer their material to thicker nanoplatelets, consistent with the kinetic instability model. Finally, we grow thin films of CdS nanoplatelets by combining “baby” CdS nanoplatelets with cadmium carboxylate and heating on a substrate. This shows that Ostwald ripening may also be exploited as a facile and versatile approach to nanoplatelet growth.

A universal growth strategy for DNA-programmed quantum dots on graphene oxide surfaces

The emerging materials of semiconductor quantum dots/graphene oxide (QDs/GO) hybrid composites have recently attracted intensive attention in materials science and technology due to their potential applications in electronic and photonic devices. Here, a simple and universal strategy to produce DNA-programmed semiconductor quantum dots/graphene oxide (QDs/GO) hybrid composites with controllable sizes, shapes, compositions, and surface properties is reported. This proof-of-concept work successfully demonstrates the use of sulfhydryl modified single-stranded DNA (S-ssDNA) as a ‘universal glue’ which can adsorb onto GO easily and provide the growth sites to synthesize CdS QDs, CdSe QDs, CdTe QDs and CdTeSe QDs with distinctive sizes, shapes and properties. Also, adapting this method, other graphene oxide-based hybrid materials which are easily synthesized in aqueous solution, including oxides, core–shell structure QDs and metal nanocrystals, would be possible. This method provided a universal strategy for the synthesis and functional realization of graphene -based nanomaterials.

Pressure-Tuned Core/Shell Configuration Transition of Shell Thickness-Dependent CdSe/CdS Nanocrystals.

Pressure is adopted as a "clean" tool to achieve a core/shell configuration transition of CdSe/CdS nanocrystals (NCs) from quasi-type II to type I. The pressure-dependent photoluminescence (PL) spectra demonstrate a sudden decrease in PL intensity, because of the enhanced rate of exciton-exciton annihilation of type I structured CdSe/CdS NCs. Likewise, the large decrease in the PL lifetime with pressure confirms that the electron wave function mainly localizes into the CdSe core, indicating the decreased separation of electrons and holes in type I band alignment. We propose that pressure increases the conduction band energy of the CdS shell but hardly changes that of the CdSe core with almost both unchanged valence band energies, thus ultimately increasing the conduction band offsets between the CdSe core and CdS shell to form the type I core/shell configuration. Our studies elucidate the significance of external pressure in determining the electronic and optical properties of core/shell nanomaterials.

Periodic FTO IOs/CdS NRs/CdSe Clusters with Superior Light Scattering Ability for Improved Photoelectrochemical Performance.

Periodic fluorine-doped tin oxide inverse opals (FTO IOs) grafted with CdS nanorods (NRs) and CdSe clusters are reported for improved photoelectrochemical (PEC) performance. This hierarchical photoanode is fabricated by a combination of dip-coating, hydrothermal reaction, and chemical bath deposition. The growth of 1D CdS NRs on the periodic walls of 3D FTO IOs forms a unique 3D/1D hierarchical structure, providing a sizeable specific surface area for the loading of CdSe clusters. Significantly, the periodic FTO IOs enable uniform light scattering while the abundant surrounded CdS NRs induce additional random light scattering, combining to give multiple light scattering within the complete hierarchical structure, significantly improving light-harvesting of CdS NRs and CdSe clusters. The high electron collection ability of FTO IOs and the CdS/CdSe heterojunction formation also contribute to the enhanced charge transport and separation. Due to the incorporation of these enhancement strategies in one hierarchical structure, FTO IOs/CdS NRs/CdSe clusters present an improved PEC performance. The photocurrent density of FTO IOs/CdS NRs/CdSe clusters at 1.23 V versus reversible hydrogen electrode reaches 9.2 mA cm-2 , which is 1.43 times greater than that of CdS NRs/CdSe clusters and 3.83 times of CdS NRs.

Improving the Power-Conversion Efficiency through Alloying in Common Anion CdZnX (X=S, Se) Nanocrystal Sensitized Solar Cells.

In this paper, we have investigated the possibility of utilizing CdZnS and CdZnSe alloy nanocrystals (NCs) as sensitizers in quantum-dot solar cells (QDSCs). The alloy NCs were synthesized by a high-temperature hot injection method and subsequently characterized through high photoluminescence quantum yield, along with larger size compared to binary NCs. Femtosecond transient absorption measurements revealed long-lived charge carriers in the alloy structure due to more structural rigidity and less defect states. Finally, the solar-cell efficiencies of the CdZnS (CdZnSe) NCs were found to be 3.05 % (3.69 %) as compared to 1.23 % (3.12 %) efficiencies for CdS (CdSe) NCs. Thus, common anion ternary NCs have been successfully utilized for solar-cell assembly and can be helpful for constructing tandem solar cells to harvest the high-energy portion of solar radiation.

High efficient light-emitting diodes with improved the balance of electron and hole transfer via optimizing quantum dot structure

Modifying the structure of quantum dots (QDs) is regarded as one of the promising way to improve the charge transfer balance of quantum dot light-emitting diodes (QLEDs). In this paper, we report highly bright Cd0.1Zn0.9S/CdSe/CdS quantum dots by optimizing the CdSe shell and CdS outer shell and explore their application in QLEDs. We find that with appropriate thicknesses of CdSe and CdS shell the charge transfer balance of the device can be improved. Comparable studies on two red QLEDs with Cd0.1Zn0.9S/CdSe/CdS and CdSe/CdS show that the external quantum efficiency (EQE) of the Cd0.1Zn0.9S/CdSe/CdS device is over 3 folds higher than its counterpart, implying that structure of the QDs plays an important role in controlling the charge transfer balance of the QLEDs.

Cu-Catalyzed Synthesis of CdZnSe–CdZnS Alloy Quantum Dots with Highly Tunable Emission

Fabrication of quantum dots (QDs) with emission covering a wide spectral region has been persistently intriguing because of their potentials in a range of practical applications such as biological labeling and imaging, solar cells, light-emitting diodes, and next-generation displays. In this work, we report the synthesis of CdZnSe–CdZnS core–shell alloy QDs through a Cu-catalyzed solid solution alloying strategy starting from CdSe–CdS core–shell QDs. The resulting CdZnSe–CdZnS alloy QDs exhibit emission profiles covering a wide wavelength range of 470–650 nm while maintaining high photoluminescence quantum yields. In addition, high morphological uniformity of the starting CdSe–CdS QDs can be largely retained in the final alloy QDs. We attribute this alloying process to the high mobility nature of Cu cations in Cd-chalcogenide crystals at elevated reaction temperatures, which allows Cu cations to act as transporting agents to transfer a Zn component into the CdSe–CdS QDs while maintaining the particle inte...

Co-sensitized TiO2 electrodes with different quantum dots for enhanced hydrogen evolution in photoelectrochemical cells

A comparative study of hydrogen evolution in devices based on cadmium chalcogenides quantum dots (CdS, CdSe and CdTe) and its combinations, sensitizing TiO2 was carried out. A maximum photocurrent of 2.7 mA cm−2 at 0 V bias, and a solar-to-hydrogen (STH) conversion efficiency of 0.9%, was obtained with CdSe QDs due to its wide absorption range. The co-sensitized device with CdS–CdSe QDs showed a higher photocurrent of 3.9 mA cm−2 with an STH of 1.2%. The improvement in hydrogen generation for electrodes sensitized with CdS in combination with CdSe or CdTe QDs, was attributed to the increased light absorption and appropriate band alignment for the enhanced charge transport.

Optical and Structural Properties of Chemical Bath Deposited Cadmium Sulphur Selenide (CdS1–xSex (0 ≤ x ≤ 1)) Thin Films

The tuneable band gap property of Cadmium-sulphur-selenide (CdS1–xSex) thin film makes it an appropriate material for a wide range of optoelec-tronic applications and this has aroused a lot of interest. In this paper, we report the study of Cadmium-sulphur-selenide (CdS1–xSex) thin films, successfully grown on commercial glass slide substrate by the chemical bath deposition technique. The effect of selenium content (x value) on the structural, and some optical properties have been studied. The bath solution contained cadmium acetate dehydrate [Cd(CH3COO)2·2H2O], so-dium selenosulphate [Na2SeSO3] and thiourea [CS(NH2)2] were used as the sources of Cd2+, Se2﹣ and S2+, respectively. Tartaric acid (C4H6O6) was used as a complexing agent. The pH of the solution was adjusted to 12 by drop-wise addition of ammonia. The bath temperature was kept at 90°C for a deposition time of 1 hour. Post deposition annealing processes of the thin films were performed in a furnace at a temperature of 400°C for two hours. Both as-deposited and annealed films were characterised by Powder X-Ray Diffraction, Scanning Electron Microscopy, UV-Visible Optical Absorption Spectroscopy and Energy Dispersive X-Ray Analysis. Optical absorption data analysis indicates that direct allowed transitions occur in the films. The band gap of the as-deposited CdS1–xSex decreased linearly from 2.34 eV to 1.48 eV, with increasing selenium content, and in the annealed samples, decreased from 1.84 eV to 1.36 eV. X-ray diffrac-tion measurements revealed, that pure CdS, and CdSe had mixed hexago-nal and cubic phases. All the remaining ternary compounds were com-posed of cubic CdS and hexagonal CdSe phases. The annealed samples showed well defined and more intense peaks, suggesting an improvement in crystallinity. The average grain size increased slightly with increasing selenium content. SEM micrographs showed that the films were compact with a smooth texture and good coverage across the entire area of the substrate.