CdS Nanowires Research Articles

Sequentially Layered CdSe/CdS Nanowire Architecture for Improved Nanowire Solar Cell Performance

The power conversion efficiency of semiconductor nanowire (NW) based solar cells as compared to quantum dot solar cell (QDSC) has remained lower, and efforts to improve the photovoltaic performance of semiconductor NWs continue. We have now succeeded in using a layered architecture of CdS and CdSe NWs for improving the photovoltaic performance of nanowire solar cell (NWSC). The photoanode designed with sequentially deposited films of CdSe and CdS NWs delivered a power conversion efficiency of 1%. This efficiency of CdSe/CdS composite is an order of magnitude improvement over single nanowire system (CdS or CdSe) based solar cell. The improvement seen in the CdSe/CdS composite film is attributed to charge rectification and improvement of electron and hole separation and transport in the opposite direction. Impedance spectroscopy demonstrates the beneficial effect of type II structure in CdSe/CdS sequential deposition through lower transport resistance, which remains a dominating effect in dictating the over...

CdS Nanowire Solar Cells: Dual Role of Squaraine Dye as a Sensitizer and a Hole Transporter

The squaraine dye (SQ) anchored onto CdS nanowires serves as a photosensitizing dye and a hole acceptor. This dual role of the squaraine dye has been successfully exploited in a nanowire solar cell to improve the photoconversion efficiency. Electrophoretic deposition of CdS NWs and CdS NWs+SQ composite onto conducting glass electrodes was performed to obtain robust photoanodes and evaluate the photovoltaic performance of nanowire solar cells (NWSCs). Whereas the sensitization property of the SQ extends the response of CdS NWSCs into the near-IR (NIR) region, its redox property facilitates shuttling of holes to the electrolyte and suppressing the charge recombination process. Transient absorption measurements confirm the formation of cation radical of the dye arising from these two processes. The dual role of the squaraine dye has enabled us to improve the power conversion efficiency of NWSCs by a factor of ∼20. Photoelectrochemical, spectroelectrochemical, and spectroscopic measurements provide insight into the multifaceted role of squaraine dye in improving the performance of NWSCs.

Plasmon–Exciton Interactions in Hybrid Structures of Au Nanohemispheres and CdS Nanowires for Improved Photoconductive Devices

We developed a method to prepare photoconductive channels of hybrid nanostructures based on Au nanohemispheres (Au NHs) and cadmium sulfide nanowires (CdS NWs) for photoconductive applications. The hybrid nanostructures exhibited enhanced absorbance, which was attributed to the strong electronic coupling between plasmons in Au NHs and excitons in CdS NWs. The photoconductive channels based on the hybrid nanostructures showed an increase in photocurrent level by ∼5× compared to bare CdS NWs. Because our strategy can be utilized to improve the photoconductivity of quite versatile photoconductive channels, it can be a powerful method for the development of various advanced optoelectronic and photovoltaic devices.

Hybrid Solar Cells Based on CdS Nanowire Arrays

Three types of hybrid solar cells based on CdS nanowire crystals have been prepared, i.e., (i) nanocrystal - polymer, (ii) nanocrystal - dye and (iii) nanocrystal - organic donor-acceptor bulk heterojunction (BHJ), and the role of CdS layer in each of the above structures has been elucidated. It has been found that CdS plays the active role of acceptor in the first two types of solar cells, whereas it plays the role of an electron-transporting (hole-blocking) layer to rectify electron flow from the organic donor-acceptor BHJ to anode in the case (iii). By changing morphology of the CdS layer from a textured continuous film to a nanowire array we demonstrate an improved efficiency of collection of charge carriers due to the increased organic-CdS interface area. Overall, a bifunctional role of the CdS nanostructured layer as a bottom electrode with a high electron affinity and as a means to increase a hybrid interface for better electron collection from the organic active layer has been demonstrated.

The Optoelectronic Properties of PbS Nanowire Field-Effect Transistors

We report on the optoelectronic properties of individual PbS nanowires prepared by gas-phase substitution reaction of pregrown CdS nanowires. The PbS nanowires synthesized by this method were found to be single crystals with high quality. A combination of electron-beam lithography and a lift-off process was utilized to fabricate individual 62-nm-thick PbS nanowire field-effect transistors (FETs). The nanowire FETs showed pronounced photoconductivity under light illumination while they were highly resistive in the dark environment. The conductivity increased by more than 40 folds in the presence of light. Our results are the first demonstration of the highly efficient photoresponse of individual single-crystalline PbS nanowires and provide insights into future works on nanostructured PbS optoelectronics.

Freestanding nanowire ring laser

We demonstrate a freestanding nanowire ring laser, assembled by splicing the two ends of a CdS nanowire via a dissolved polymer nanowire. With ring diameter of less than 50 μm, the free-standing nanowire ring laser shows low lasing threshold, high robustness, and excellent mechanical flexibility. Also, the nanowire ring laser works well in liquid environment, showing the possibility of integrating the nano-ring laser into an optofluidic system.

Wavelength Tunable Single Nanowire Lasers Based on Surface Plasmon Polariton Enhanced Burstein–Moss Effect

Wavelength tunable semiconductor nanowire (NW) lasers are promising for multifunctional applications ranging from optical communication to spectroscopy analysis. Here, we present a demonstration of utilizing the surface plasmon polariton (SPP) enhanced Burstein-Moss (BM) effect to tune the lasing wavelength of a single semiconductor NW. The photonic lasing mode of the CdS NW (with length ~10 μm and diameter ~220 nm) significantly blue shifts from 504 to 483 nm at room temperature when the NW is in close proximity to the Au film. Systematic steady state power dependent photoluminescence (PL) and time-resolved PL studies validate that the BM effect in the hybrid CdS NW devices is greatly enhanced as a consequence of the strong coupling between the SPP and CdS excitons. With decreasing dielectric layer thickness h from 100 to 5 nm, the enhancement of the BM effect becomes stronger, leading to a larger blue shift of the lasing wavelength. Measurements of enhanced exciton emission intensities and recombination rates in the presence of Au film further support the strong interaction between SPP and excitons, which is consistent with the simulation results.

Efficient Visible-Light Photocatalytic Hydrogen Evolution and Enhanced Photostability of Core/Shell CdS/g-C3N4Nanowires

CdS/g-C3N4 core/shell nanowires with different g-C3N4 contents were fabricated by a combined solvothermal and chemisorption method and characterized by X-ray powder diffraction, scanning electronic microscopy, transmission electron microscopy, and UV-vis diffuse reflection spectroscopy. The photocatalytic hydrogen-production activities of these samples were evaluated using Na2S and Na2SO3 as sacrificial reagents in water under visible-light illumination (λ≥420 nm). The results show that after a spontaneous adsorption process g-C3N4 is successfully coated on CdS nanowires with intimate contact and can significantly improve the photocatalytic hydrogen-production rate of CdS nanowires, which reaches an optimal value of up to 4152 μmol h(-1) g(-1) at the g-C3N4 content of 2 wt %. More importantly, g-C3N4 coating can substantially reinforce the photostability of CdS nanowires even in a nonsacrificial system. The synergic effect between g-C3N4 and CdS, which can effectively accelerate the charge separation and transfer corrosive holes from CdS to robust C3N4, was proposed to be responsible for the enhancement of the photocatalytic activity and photostability. The possible conditions necessary for the synergic effect to work in a CdS/g-C3N4 core/shell configuration is also discussed.

Fabrication of CdS/Hg(1−x)CdxTe nanowire heterostructures on conductive glass using templated electrodeposition

Single-material and heterojunction nanowires were fabricated from CdS and Hg(1−x)CdxTe (MCT) in anodic aluminum oxide templates grown on transparent conductive oxide coated glass substrates. Structural and compositional analyses were carried out by electron microscopy, elemental analysis and x-ray diffraction. CdS was deposited using potentiostatic electrodeposition, forming CdS nanowires with a 1:1 stoichiometry and wurtzite structure. MCT was also deposited using potentiostatic electrodeposition, forming MCT nanowires with a stoichiometry of Hg0.24Cd0.76Te and a zinc blende structure. Annealing of the electrodeposited MCT nanowires increased crystallite size from ~9nm to ~23nm in the (111) direction. Heterojunction nanowires were prepared by sequential electrodeposition of CdS and MCT with control over the length and diameter. These materials have a desirable band gap and geometry for multiple-exciton generation studies for nanostructured photovoltaics applications.

One-dimensional embedded cluster approach to modeling CdS nanowires

We present an embedded cluster model to treat one-dimensional nanostructures, using a hybrid quantum mechanical/molecular mechanical (QM/MM) approach. A segment of the nanowire (circa 50 atoms) is treated at a QM level of theory, using density functional theory (DFT) with a hybrid exchange-correlation functional. This segment is then embedded in a further length of wire, treated at an MM level of theory. The interaction between the QM and MM regions is provided by an embedding potential located at the interface. Point charges are placed beyond the ends of the wire segment in order to reproduce the Madelung potential of the infinite system. We test our model on the ideal system of a CdS linear chain, benchmarking our results against calculations performed on a periodic system using a plane-wave DFT approach, with electron exchange and correlation treated at the same level of approximation in both methods. We perform our tests on pure CdS and, importantly, the system containing a single In or Cu impurity. We find excellent agreement in the determined electronic structure using the two approaches, validating our embedded cluster model. As the hybrid QM/MM model avoids spurious interactions between charged defects, it will be of benefit to the analysis of the role of defects in nanowire materials, which is currently a major challenge using a plane-wave DFT approach. Other advantages of the hybrid QM/MM approach over plane-wave DFT include the ability to calculate ionization energies with an absolute reference and access to high levels of theory for the QM region which are not incorporated in most plane-wave codes. Our results concur with available experimental data.

Charge Transport in 1-D Nanostructured CdS Dye Sensitized Solar Cell

Charge transport in eosin yellow sensitized CdS 1-D nanostructures is studied. Direct conduction pathway for electron transport in nanowires enhances Voc in CdS nanowires compared to nanorods and nanoparticles. J-V characterization of nanowires results in improved efficiency of 0.184% due to fewer interparticle connections. Increase in Jsc is observed by coating CdS 1-D nanostructures on TiO2 substrate which reduces rate of recombination and photocorrosive nature of CdS photoanodes. Enhancement in efficiency up to 0.501% is achieved for CdS 1-D nanostructures DSSCs on TiO2 substrate.

Room temperature ferromagnetism in Mn doped CdS nanowires

CdS:Mn (0%, 1.9% and 3%) nanowires with significant room-temperature ferromagnetism have been synthesized by chemical vapor deposition method using Au as catalyst. The X-ray diffraction, Raman spectroscopy and transmission electron microscopy analyses of these samples showed the formation of impurity free crystals with wurtzite CdS structure. SEM results reveal a uniform size distribution of the nanowires throughout the substrate. Photoluminescence spectra of undoped CdS reveals a weak band edge emission and a strong red emission related to surface defects. The luminescence is found to be decreased with Mn doping. Quenching of red emission intensity observed with the doping of Mn ions into CdS confirmed the changed defect structure in Mn doped CdS lattice. The enhancement of room temperature ferromagnetism was observed with increasing Mn doping concentration.

General Synthesis and White Light Emission of Diluted Magnetic Semiconductor Nanowires Using Single-Source Precursors

Because of the fundamental properties and possible applications in spin-based electronics and photonics, diluted magnetic semiconductor nanowires are actively pursued. Here we report a general and facile solution synthetic strategy to prepare colloidal diluted magnetic semiconductor nanowires through solution-liquid–solid (SLS) doping approach using single-source precursors. On the basis of this strategy, transition metal ions such as Mn and Eu doped CdS nanowires were successfully synthesized and characterized. The material characterizations demonstrated that the doping process is nucleation controlled. We further investigated the Mn doping effects on nanowire growth as well as their photoluminescence properties. The Mn doped CdS nanowires exhibit photoluminescence emission related to the excitonic magnetic polaron in CdS, single Mn2+ ion and Mn–S–Mn centers as well as trap states, evidenced by the time-resolved photoluminescence spectra and magnetic measurements. With the increase of Mn precursor that u...

CdS nanowires: Ultra-long growth and enhanced field emission properties

Here, we report the synthesis of ultra-long CdS nanowires with aspect ratio ∼8 × 104 by simple route of thermal evaporation technique. A change in the vertical arrangement of quartz boats leads in to the synthesis of ultra-long CdS nanowires via high degree of condensation. This technique is seen to be cost effective and easy. The growth of the nanowires is found to be increased very rapidly from few micrometers to few millimeters. The possible reason for the growth of the ultra-long CdS nanowires is discussed in detail. The turn-on field defined for the current density of ∼0.1 μA/cm2 has been found to be ∼1.4, 1.45, 1 and 0.17 V/μm for specimen A, B, C and D (specimens A–D, synthesized by variation in synthesis parameters) respectively. The turn-on field of the specimen D (∼0.17 V/μm) is found to be quite superior than the value reported for other CdS nanoforms which is very remarkable. Simple way of bulk fabrication leads to the low turn-on value which indicates a possible use of the present emitter in the micro/nanoelectronics devices.

Solvothermal synthesis and characterization of one-dimensional CdS nanowires

One-dimensional single crystal wurtzite phase CdS nanowires were successfully synthesized through a facile solvothermal method. The obtained CdS nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis absorption spectroscopy, Raman spectrum, N2 adsorption–desorption isotherm experiment and photoluminescence spectrum (PL). The SEM and TEM results show that the diameter of the obtained CdS nanowires is about 50nm and the length is several micrometers, growing along [100] direction. UV–vis spectrum exhibits a strong absorption peak centered at 486nm. Raman spectrum shows there are three vibration modes at 300, 600 and 900cm−1. N2 adsorption–desorption isotherm experiment shows that the BET specific surface area of CdS nanowires is 21.97m2g−1. Room temperature photoluminescence spectrum shows the CdS nanowires has one emission band at 524nm and a shoulder band at 700nm.

Growth of CdS nanowire crystals: Vapor–liquid–solid versus vapor–solid mechanisms

The difference in the growth conditions, crystalline structure and morphology of CdS nanowire crystals synthesized via the vapor–solid (VS) mechanism on bare substrates and via the vapor–liquid–solid (VLS) mechanism using gold catalyst, respectively, has been studied. It has been found that the growth of CdS nanowire crystals by the VS mechanism depends on the substrate material used and that the roughness of the substrate surface is also an important parameter influencing nucleation of CdS nanowires. The crystals obtained by VLS demonstrated perfect crystal plane orientation and the wurtzite crystallographic symmetry, whereas the crystals obtained by VS mechanism showed transition regions with more rich morphology resulting in changes of the crystalline plane orientation of the growing nanowire, as well as inhomogeneous stoichiometry along the crystal. The rich morphology was attributed to the competition of nucleation rates and growth rates among different crystallographic planes which may be affected by changes in temperature regimes of the growing zone.

Cu2O-decorated CdS nanostructures for high efficiency visible light driven hydrogen production

Cu2O-decorated CdS nanostructures are developed as highly efficient photocatalysts for hydrogen evolution from visible-light driven photocatalytic water splitting. The type II heterojunctions formed at the Cu2O/CdS interfaces facilitate charge separation that promotes photocatalytic water splitting and thus markedly improves the hydrogen evolution efficiency. For Cu2O decorated CdS nanobeads (NB), a milli-molar level specific hydrogen evolution rate of 4.76 mmol/h g is achieved, 72 times that achieved by plain CdS NBs, under irradiation of a 400 W light source using a mixture of Na2S and NaSO3 as the sacrificial reagent. The improvements in hydrogen evolution acquired from the Cu2O decoration for CdS NBs are much greater than those attained for CdS nanoparticles (NPs) and CdS nanowires (NWs). The success of using CdS NBs as the hosting base for Cu2O decoration is attributed to the much better exposed CdS surfaces after the treatment, enabling direct contact of CdS with the reactant solution for hydrogen evolution, while the Cu2O surfaces are also exposed to contact the sacrificial reagent for scavenging holes.

Carbon fiber as a flexible quasi-ohmic contact to cadmium sulfide micro- and nanocrystals

A conductive pyrolytic carbon fiber (CF) has been found to serve as an alternative material to metal electrodes, since it forms an Ohmic contact to CdS crystals. The methods of preparation of polycrystalline layers and nanocrystalline arrays of CdS are described that allow formation of an ohmic or quasi-ohmic contact to CF. It is shown that the ohmic contact between the CF and polycrystalline CdS layer is stable for at least several months and its exploitation characteristics are not worse than the indium contact. Advantages of the CF electrode, such as thermostability to extremely high temperatures and low cost are discussed. CdS nanowire arrays grown on a carbon fiber.

Scalable Alignment of CdS Nanowires Based on Efficient Roll-On Transfer Technique

A roll-on transfer strategy is developed to enable large-scale and uniform assembly of CdS nanowires on various rigid and flexible substrate materials. In this method, the CdS nanowires were synthesized by the hydrothermal method. The dispersed CdS NWs could be firstly aligned and selectively deposited at the micro/nanochannels between aligned nanofibers on the surface of the donor roller as a result of evaporation-induced flow and capillary action, and then the directional and aligned transfer of the CdS NWs from the donor roller to a receiver substrate via roll-on transfer technique. Finally, a device structures consisting of the nanowire channel and two metal electrodes was fabricated. The electrical property of this device was observed.

Controlling the Crystallinity of Electrochemically Deposited CdS Nanowires

This report describes two distinct growth regimes occurring during the templated electrochemical deposition of CdS nanowires. The abundance of Cd2+ ions at the growth front dictates crystal nucleation and growth processes. At high Cd2+ concentration, randomly oriented polycrystalline material is formed, whereas local depletion of Cd2+ results in highly oriented crystals with the [002] crystalline direction aligned with the nanowire axis. Single nanowires exhibiting both regions were produced for direct imaging of the microstructure associated with these regimes. The current dependence of the time needed to locally deplete Cd2+ allowed for the extraction of a diffusion coefficient for Cd2+ of 1.23 × 10–6 cm2/s, which reflects reduced diffusion in nanoscale channels. Knowledge of these growth regimes and the parameters governing them allows for the growth of materials with targeted structural properties. Specifically, single-crystal materials can be preferentially formed by depositing at relatively high growth currents or by reducing the initial concentration of the Cd precursor in solution.