Conduction Band Of CdS Research Articles

Investigation of the physical properties of the Yb nanosandwiched CdS films

In this study, the effects of the sandwiching of a 70 nm thick ytterbium film between two layers of CdS on the structural, compositional, optical and electrical properties are investigated. The X-ray diffraction, scanning electron microscopy, energy dispersion X-ray, visible light spectroscopy and impedance spectroscopy techniques are employed to achieve these effects. It was observed that, the nanosandwiching of Yb between two 500 nm thick films of CdS enhances the crystalline nature of the films without altering the lattice parameters. Particularly, the grain size is increased by 25%, the strain, the defect density and the stacking faults are reduced by 31.5%, 43.7% and 25%, respectively. Optically, the Yb nanosandwiching is observed to enhance the visible light absorbability by at least 2.7 times of the whole range and by 8 times at 1.64 eV. The enhancement of the absorbability is associated with shrinking in the band gap and more interband states. In addition, an increase in the real part of the dielectric constant by 54% is observed when Yb was nanosandwiched in the CdS structure. The modeling of the imaginary part allowed exploring the electron-plasmon interaction parameters. A remarkable increase in the drift mobility from 281 to 996 cm2/Vs associated with plasmon frequency enhancement from 0.84 to 1.38 GHz was determined upon Yb nanosandwiching. The effectiveness of this modeling was verified from the impedance spectra in the frequency domain of 0.01–1.80 GHz, which revealed wave trapping property of ideal values of return loss at notch frequency of 1.35 GHz. Furthermore, the electrical resistivity measurements on the studied samples have shown that the presence of Yb reduced the electrical resistivity and shifts the donor level closer to the conduction band of CdS. The studies nominate the nanosandwiched CdS for use in optical and microwave technologies as dual devices.

Hydrogen generation by photocatalytic reforming of glucose with heterostructured CdS/MoS2 composites under visible light irradiation

A binary heterostructured CdS/MoS2 flowerlike composite photocatalysts was synthesized via a simple one-pot hydrothermal method. This photocatalyst demonstrated higher photocatalytic hydrogen production activity than pure MoS2. The heterojunction formed between MoS2 and CdS seems to promote interfacial charge transfer (IFCT), suppress the recombination of photogenerated electron–hole pairs, and enhance the hydrogen generation. Based on the good match between the conduction band (CB) edge of CdS and that of MoS2, electrons in the CB of CdS can be transferred to MoS2 easily through the heterojunction between them, which prevents the accumulation of electrons in the CB of CdS, inhibiting photocorrosion itself and greatly enhancing stability of catalyst. Hydrogen evolution reaction (HER) using Na2S/Na2SO3 or glucose as sacrificial agents in aqueous solution was investigated. The ratio between CdS and MoS2 plays an important role in the photocatalytic hydrogen generation. When the ratio between CdS and MoS2 reaches 40 wt%, the photocatalyst showed a superior H2 evolution rate of 55.0 mmol g−1 h−1 with glucose as sacrificial agent under visible light, which is 1.2 times higher than using Na2S/Na2SO3 as sacrificial agent. Our experimental results demonstrate that MoS2-based binary heterostructured composites are promising for photocorrosion inhibition and highly efficient H2 generation.

Construction of an all-solid-state artificial Z-scheme system consisting of Bi2WO6/Au/CdS nanostructure for photocatalytic CO2 reduction into renewable hydrocarbon fuel

An all-solid-state Bi2WO6/Au/CdS Z-scheme system was constructed for the photocatalytic reduction of CO2 into methane in the presence of water vapor. This Z-scheme consists of ultrathin Bi2WO6 nanoplates and CdS nanoparticles as photocatalysts, and a Au nanoparticle as a solid electron mediator offering a high speed charge transfer channel and leading to more efficient spatial separation of electron–hole pairs. The photo-generated electrons from the conduction band (CB) of Bi2WO6 transfer to the Au, and then release to the valence band (VB) of CdS to recombine with the holes of CdS. It allows the electrons remaining in the CB of CdS and holes in the VB of Bi2WO6 to possess strong reduction and oxidation powers, respectively, leading the Bi2WO6/Au/CdS to exhibit high photocatalytic reduction of CO2, relative to bare Bi2WO6, Bi2WO6/Au, and Bi2WO6/CdS. The depressed hole density on CdS also enhances the stability of the CdS against photocorrosion.

Electronic structures of Cu2ZnSnSe4 surface and CdS/Cu2ZnSnSe4 heterointerface

We studied the electronic structures of the Cu2ZnSnSe4 (CZTSe) surface and CdS/CZTSe heterointerface using X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and inversed photoemission spectroscopy (IPES) systems. These measurement systems are connected to the CdS deposition chamber via a transport chamber under ultrahigh vacuum. We revealed that the conduction band offset (CBO) and valence band offset (VBO) are +0.56 and +0.89 eV, respectively, at the CdS/CZTSe heterointerface. A positive CBO value, referred to as a “spike” structure, indicates that the position of the conduction band of CdS becomes higher than that of the absorber layer. Despite such a large spike structure in the conduction band at the interface, a conversion efficiency of 8.7% was obtained for our CdS/CZTSe heterojunction solar cells. Moreover, we found that the Fermi level at the CZTSe surface is located near the center of the bandgap and that the hole deficiency near the CZTSe surface is stronger than that inside the bulk CZTSe. We also found that Fermi level pinning did not occur at the CZTSe surface or CdS/CZTSe heterointerface by XPS.

Enhanced Solar Hydrogen Generation by a Heterojunction of Perovskite-type La2 Ti2 O7 Nanosheets Doped with CdS Quantum Dots.

A heterojunction of a perovskite-type La2 Ti2 O7 (LTO)/CdS quantum dot (QD) nanocomposite was prepared by the chemical bath deposition method. The solar-light-driven H2 generation results show that this CdS QDs/LTO heterojunction exhibits great improvement in the photocatalytic H2 production and its photoelectrochemical properties in comparison with pure CdS QDs and LTO nanosheets. A possible enhanced mechanism of photoinduced interfacial charge transfer between CdS and LTO is proposed for the heterojunction. The shift of the CdS conduction band (CB) edge can enlarge the CB potential difference between CdS QDs and LTO, enhancing transferred driven force of the interfacial electrons and finally improving the two components' separation activity of photogenerated carriers. This study provides a promising method for constructing an efficient photoinduced interfacial charge transfer over LTO and CdS QD heterojunctions for photocatalytic hydrogen production.

Engineered band structure for an enhanced performance on quantum dot-sensitized solar cells

A photon-to-current efficiency of 2.93% is received for the Mn-doped CdS (MCdS)-quantum dot sensitized solar cells (QDSSCs) using Mn:ZnO (MZnO) nanowire as photoanode. Hydrothermal synthesized MZnO are spin-coated on fluorine doped tin oxide (FTO) glass with P25 paste to serve as photoanode after calcinations. MCdS was deposited on the MZnO film by the successive ionic layer adsorption and reaction method. The long lived excitation energy state of Mn2+ is located inside the conduction band in the wide bandgap ZnO and under the conduction band of CdS, which increases the energetic overlap of donor and acceptor states, reducing the “loss-in-potential,” inhibiting charge recombination, and accelerating electron injection. The engineered band structure is well reflected by the electrochemical band detected using cyclic voltammetry. Cell performances are evidenced by current density-voltage (J-V) traces, diffuse reflectance spectra, transient PL spectroscopy, and incident photon to current conversion efficiency characterizations. Further coating of CdSe on MZnO/MCdS electrode expands the light absorption band of the sensitizer, an efficiency of 4.94% is received for QDSSCs.

Cadmium Sulphide-Reduced Graphene Oxide-Modified Photoelectrode-Based Photoelectrochemical Sensing Platform for Copper(II) Ions.

A photoelectrochemical (PEC) sensor with excellent sensitivity and detection toward copper (II) ions (Cu2+) was developed using a cadmium sulphide-reduced graphene oxide (CdS-rGO) nanocomposite on an indium tin oxide (ITO) surface, with triethanolamine (TEA) used as the sacrificial electron donor. The CdS nanoparticles were initially synthesized via the aerosol-assisted chemical vapor deposition (AACVD) method using cadmium acetate and thiourea as the precursors to Cd2+ and S2-, respectively. Graphene oxide (GO) was then dip-coated onto the CdS electrode and sintered under an argon gas flow (50 mL/min) for the reduction process. The nanostructured CdS was adhered securely to the ITO by a continuous network of rGO that also acted as an avenue to intensify the transfer of electrons from the conduction band of CdS. The photoelectrochemical results indicated that the ITO/CdS-rGO photoelectrode could facilitate broad UV-visible light absorption, which would lead to a higher and steady-state photocurrent response in the presence of TEA in 0.1 M KCl. The photocurrent decreased with an increase in the concentration of Cu2+ ions. The photoelectrode response for Cu2+ ion detection had a linear range of 0.5–120 μM, with a limit of detection (LoD) of 16 nM. The proposed PEC sensor displayed ultra-sensitivity and good selectivity toward Cu2+ ion detection.

Light-induced cation exchange for copper sulfide based CO2 reduction.

Copper(I)-based catalysts, such as Cu2S, are considered to be very promising materials for photocatalytic CO2 reduction. A common synthesis route for Cu2S via cation exchange from CdS nanocrystals requires Cu(I) precursors, organic solvents, and neutral atmosphere, but these conditions are not compatible with in situ applications in photocatalysis. Here we propose a novel cation exchange reaction that takes advantage of the reducing potential of photoexcited electrons in the conduction band of CdS and proceeds with Cu(II) precursors in an aqueous environment and under aerobic conditions. We show that the synthesized Cu2S photocatalyst can be efficiently used for the reduction of CO2 to carbon monoxide and methane, achieving formation rates of 3.02 and 0.13 μmol h(-1) g(-1), respectively, and suppressing competing water reduction. The process opens new pathways for the preparation of new efficient photocatalysts from readily available nanostructured templates.

CuO-induced signal amplification strategy for multiplexed photoelectrochemical immunosensing using CdS sensitized ZnO nanotubes arrays as photoactive material and AuPd alloy nanoparticles as electron sink

In this work, multiplexed photoelectrochemical (PEC) immunoassays are introduced into an indium tin oxide (ITO) device. Firstly, the ITO device is fabricated using a simple acid etch treatment method. Secondly, AuPd alloy nanoparticles are electro-deposited on ITO working electrodes as electron sink to construct the immunosensor platform. After that, ZnO nanotubes (ZNTs) arrays are synthesized via chemical etching of ZnO nanorods that are grown on AuPd surface by electrochemical deposition method. Subsequently, CdS is electro-deposited on ZNTs arrays and used as photoactive material. Then, CuO nanoseeds are labeled with signal antibodies and firstly used as PEC signal amplification label. The introduction of CuO brings signal amplification because of the conduction band (CB) of both CuO and ZnO are lower than that of CdS, CuO will compete the photo-induced electrons in CB of CdS with ZnO, leading to the decrease of the photocurrent intensity. Using cancer antigen 125, prostate specific antigen and α-fetoprotein as model analytes, the proposed immunoassay exhibits excellent precision and sensitivity. Meanwhile, this work provides a promising, addressable and simple strategy for the multi-detection of tumor markers.

Photoluminescence quenching of a CdS nanoparticles/ZnO nanorods core–shell heterogeneous film and its improved photovoltaic performance

CdS nanoparticles/ZnO nanorods core–shell heterogeneous thin films were successfully fabricated using a chemical bath deposition process. X-ray diffraction (XRD), optical spectroscopy and field emission scanning electron microscopy (FE-SEM) were used for the characterization of the samples. Photoluminescence (PL) properties of the CdS nanoparticles/ZnO nanorods core-shell heterogeneous films were studied using PL spectroscopy. The injection of electrons from the CdS conduction band into the ZnO conduction band upon excitation was confirmed by PL quenching. The PL quenching in the present study demonstrated that more than one CdS nanoparticle is capable of networking with the single ZnO nanorod and taking an active part in the charge injection process. By attaching the CdS nanoparticles, the authors found the surface photovoltaic characteristics of ZnO were changed significantly. With a liquid electrolyte as the hole transport medium, CdS nanoparticles/ZnO nanorods core–shell heterogeneous film exhibited a short-circuit current density of 3.62mAcm−2 and an open-circuit voltage of 643mV with a total light-to-electricity power conversion efficiency of 1.48% under visible light.

Electron Extraction Dynamics in CdSe and CdSe/CdS/ZnS Quantum Dots Adsorbed with Methyl Viologen

Semiconductor quantum dots (QDs) composed of multiple components are playing an important role in solar energy conversion as light harvesting materials. Electron extraction dynamics in CdSe and core/shell CdSe/CdS/ZnS colloidal QDs are studied by femtosecond transient absorption spectroscopy in this Article. Our study demonstrates that, in the presence of the commonly used electron acceptor, methyl viologen (MV2+), electrons in the 1S state of CdSe QDs can be effectively extracted with a time constant less than 150 fs. With regard to type I core/shell CdSe/CdS/ZnS QDs, 400 nm excitation will mainly populate the CdS first, due to its large absorption cross section at around that wavelength. Electrons from the conduction band of CdS then can be directly extracted by MV2+ before transferring to core CdSe. Therefore, MV2+ can serve as an efficient bridge to extract electrons from the shell of type I QDs. As compared to the bare QDs, core/shell QDs have slower charge separation and much slower recombination rates. Thus, the core/shell QDs are beneficial for designing solar cells.

Decoration of Fe3O4 Base Material with Pd Loaded CdS Nanoparticle for Superior Photocatalytic Efficiency

Decorated ternary Pd@CdS@Fe3O4 nanoarchitectures are synthesized by judicious loading of CdS nanoparticles without functionalizing the surface of the base materials, i.e., Fe3O4 and CdS. Here we have adopted a unique method to prepare Fe3O4 nanoparticles. In this ternary composite ferromagnetic Fe3O4 behaves as the catalyst carrier, CdS is used as semiconductor, and loaded Pd due to its high electron affinity behaves as a electron scavenger. CdS inherits visible light absorbing capability. Here Pd2+ is reduced to Pd upon deposition onto the CdS nanoparticles by the anionic S2–. Then the ternary composite exhibits pronounced photocatalytic activity toward Rhodamine B oxidation under visible light irradiation in the yellow region. This composite happens to be much more efficient than that of pure CdS and CdS@Fe3O4 composite. Metallic Pd, due to its high electron withdrawing property, uptakes the electrons from the conduction band of CdS and increases the oxidative power of CdS. Because of the presence of Fe3O4 in the composite, the catalyst shows ferromagnetism, and thus after the photocatalytic experiments the catalyst is easily isolated from the reaction mixture. The efficiency of the photocatalyst decreases after five cycles because of the disintegration of the particle. The ternary composite serves as a convenient and efficient photocatalyst for degradation of dye molecules leading to the purification of water.

A new signal amplification strategy of photoelectrochemical immunoassay for highly sensitive interleukin-6 detection based on TiO2/CdS/CdSe dual co-sensitized structure

Dual co-sensitized structure of TiO2/CdS/CdSe was designed to develop a novel photoelectrochemical immunoassay for highly sensitive detection of human interleukin-6 (IL-6). To construct a sensing electrode, TiO2/CdS hybrid was prepared by successive adsorption and reaction of Cd2+ and S2− ions on the surface of TiO2 and then was employed as matrix for immobilization of anti-IL-6 antibody, whereas CdSe QDs linked to IL-6 were used for signal amplification via the specific antibody–antigen immunoreaction between anti-IL-6 and IL-6–CdSe bioconjugate. Greatly enhanced sensitivity for IL-6 detection was derived from the new co-sensitization signal amplification strategy. First, the TiO2/CdS/CdSe co-sensitized structure extended the absorption range to long wavelength of white light, which adequately utilized the light energy. Second, the TiO2/CdS/CdSe co-sensitized structure possessed stepwise band-edge levels favoring ultrafast transfer of photogenerated electrons and significantly prompted the photoelectrochemical performance. Besides, the introduction of CdSe effectively prevented the recombination of photogenerated electrons in the conduction band of CdS, further causing an enhanced photocurrent. Accordingly, upon the co-sensitization strategy, a novel immunoassay based on the competitive binding of anti-IL-6 antibody with IL-6 antigen and IL-6–CdSe bioconjugate was developed, and it exhibited a wide linear range from 1.0pg/mL to 100ng/mL with a low detection limit of 0.38pg/mL for IL-6 detection. The proposed co-sensitization strategy presented high sensitivity, reproducibility, specificity and stability, and also opened up a new promising platform for detection of other biomarkers.

Sensitive Surface States and their Passivation Mechanism in CdS Quantum Dots

We report on phase sensitive surface states of CdS quantum dots (QDs), where it is noticed that a simple phase change from dispersion to solid has shown significant influence on the emission spectrum. As the solvent evaporates from the dispersion, apparently yellow dispersion transforms into a white light emitter because of the conformal changes in the polymer that surrounds the QDs. In turn, these changes catalyze the emission from three specific wavelengths in the blue region of the spectrum, shifting the surface defects closer to the conduction band of CdS. In the phase change from dispersion to solid, flexible and dangling polymer chains are transformed into rigid moieties that can be treated as a modified chemical environment. Furthermore, to ascertain the origin of the new emission lines, we have studied a dipole interaction-based passivation mechanism between QDs and the polymer. The proposed mechanism may be valuable for designing future QD-based fluorophores and explains the sensitivity of the su...

ZnS:Mn2+ nanoparticles as compact layer to enhance the conversion efficiency of CdS QD-sensitized solar cells

The CdS quantum dots sensitized ZnO nanorods solar cells with ZnS:Mn2+ nanoparticles as compact layer were fabricated. The effects of Mn2+ doping concentration on the photovoltaic performance of ZnO/ZnS:Mn2+ photoanode were investigated. Besides the suppression of the back transfer of photoelectrons by ZnS:Mn2+ compact layer, with the increase of Mn2+ doping concentration, the energy level of conduction band of ZnS:Mn2+ nanoparticles turned lower, which is beneficial for the charge transfer from the conduction band of CdS. Thus, the photoelectric conversion efficiency of the cell with ZnS:Mn2+ (5%) exhibited ∼3.6 folds increments of as-synthesized bare ZnO solar cell.

Enhanced photocatalytic activity and stability of semiconductor by Ag doping and simultaneous deposition: the case of CdS

Herein, it is demonstrated how the photocatalytic activity and stability of a semiconductor can be enhanced through metal doping and simultaneous deposition in the case of CdS. The CdS which is doped and simultaneously deposited by Ag (denoted as Ag–CdS thereafter) is successfully prepared by a one-step hydrothermal method. The prepared Ag–CdS samples have enhanced photocatalytic activity under simulated sunlight compared with pure CdS and Ag-deposited CdS for organic pollutant degradation and H2 production from water splitting. The main reason for the enhanced activity is due to the fast transfer of photogenerated electrons from the conduction band of CdS to Ag nanoparticles on the surface, which suppresses the recombination of photogenerated electrons and holes. As for the enhanced stability of the Ag–CdS sample, the doping with Ag creates an acceptor energy level near the valence band of CdS. The holes will inject into the acceptor energy level freely, leading to the weak oxidative ability of holes in the excited semiconductor. Moreover, the more stable and more easily formed chemical bond between Ag+ substituted for Cd2+ and S2+ makes the sample more stable than Ag-deposited CdS. The Ag–CdS photocatalyst with high activity and stability can be used in future applications.

Ultrafast Electronic Delocalization in CdSe/CdS Quantum Rod Heterostructures

Femtosecond cross-polarized transient grating (CPTG) and polarization anisotropy were used to probe the extent of electronic delocalization in CdSe/CdS quantum rod heterostructures (QRH) with a "dot-in-rod" geometry. The alignment of the bulk valence and conduction band edges of CdSe and CdS suggest a "type I" band configuration, leading to localization of both the electron and hole on the CdSe seed, but size quantization effects make the distinction less clear. Photoexcited electrons in 2.1 and 2.9 nm diameter structures have considerable excess kinetic energy above the CdS conduction band and show clear evidence of electron delocalization into the surrounding shell. However, the dependence of the CPTG decay rate on aspect ratio for 2.9 nm seeded QRHs is minimal, suggesting that the delocalization is mostly isotropic (i.e., not preferentially along the rod length). The rates for the 2.1 and 2.9 nm QRHs fall in line with expected trends based on effective exciton size. The 4.2 nm diameter structures also lack any rod length dependence of the CPTG decay and instead exhibit a biexponential decay that is indicative of coupled pathways for fine structure relaxation, likely due to anisotropic interfacial strain. CPTG is found to serve as a unique tool for determining charge transfer and delocalization in nanoheterostructures, which can rarely be predicted accurately from examination of bulk band offsets.

Effect of Zn incorporation into CuInS2 solar cell absorbers on microstructural and electrical properties

Zn incorporation into CuInS2 absorbers is found to increase the open-circuit voltage but decrease the short-circuit current of the corresponding thin-film solar cells. In this article, we study the effect of Zn incorporation into CuInS2 absorbers with a focus on the mechanisms leading to the measured changes in the electrical properties of the solar cells. Solar cells with varying Zn concentrations in their absorbers are characterized via the application of transmission electron microscopy, quantum efficiency, and current-voltage measurements, as well as admittance, x-ray photoelectron and photoluminescence spectroscopy. A Zn accumulation on the absorber side of the CuInS2–CdS interface and a higher structural defect density within the absorber are found after Zn incorporation. Capacitance, quantum efficiency, and current-voltage measurements in combination with device simulations suggest that Zn incorporation induces or enhances a shallow donor at the CuInS2–CdS interface. The interface defect pins the Fermi level close to the CdS conduction band, leading to an inversion at the heterointerface and thus reducing the recombination at interface defects and increasing the open-circuit voltage. A shallow bulk acceptor about 0.15 eV above the valence band edge is observed to increase with increasing Zn concentration in the CuInS2 absorbers and is responsible for a gradual decrease in the short-circuit current and the gain in the open-circuit voltage as the Zn concentration increases.

Band alignment at the Cu2ZnSn(SxSe1−x)4/CdS interface

Energy band alignments between CdS and Cu2ZnSn(SxSe1−x)4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes.

Scanning spreading resistance microscopy of undoped CdS/ZnSSe multiple quantum well heterostructure

AbstractWe carried out scanning spreading resistance microscopy (SSRM) investigation of the undoped CdS/ZnSSe multiple quantum well (MQW) heterostructure under different illumination conditions. To study this effect we illuminated the probe–sample point contact with the radiation of a halogen lamp (HL) (hν = 1.2–3.1 eV). In spite of the fact that the photon energy of the built‐in atomic force microscope laser (BL) (1.9 eV) is smaller than the band gap energy of the CdS (2.46 eV) and the energy of transitions between ZnSSe valence band and CdS conduction band (2.2 eV) it, nevertheless, influences the visualization, possibly due to Franz–Keldysh effect. It was found that all layers of the structure can be visualized only under negative sample potential, indicating Schottky barrier formation at probe–sample contact. We estimated the carrier concentration in QWs on the basis of simple Schottky diode theory, taking into account spreading resistance Rs.