ZnS Layer Research Articles

ROLE OF Au NANOSHEETS IN ENHANCING THE PERFORMANCE OF Yb/ZnS/CdS/Au TUNNELING PHOTOSENSORS

In this study, the effects of Au nanosheets of thicknesses of 50 nm on the structural, electrical and photoelectrical properties of Yb/ZnS/CdS/Au (ZAC-0) devices is considered. Stacked layers of ZnS and CdS which are prepared by the thermal evaporation technique onto Yb substrates under vacuum pressure of 10-5 mbar exhibits rectifying characteristics. For these diodes a reverse to forward current ratios of ~105 at biasing voltage of 0.60 V is determined. Insertion of Au nanosheets between the stacked layers of ZnS and CdS increased the current values by three orders of magnitude and changed the current conduction mechanism from thermionic emission to tunneling under reverse biasing conditions. The ZAC-0 device, exhibit a barrier height lowering and barrier widening upon insertion of Au nanosheets. After the participation of Au nanosheets in the structure of the ZAC-0 devices, large photosensitivity and responsivity accompanied with high external quantum efficiency is observed. The responsivity to 406 nm laser radiation is biasing voltage dependent and reaches 135 mA/W at 0.60 V. The features of the Yb/ZnS/Au/CdS/Au photosensors nominate them as promising candidates for use in light communication technology as signal receivers.

Observation of mixed types of energy gaps in some II–VI semiconductors nanostructured films: towards enhanced solar cell performance

All solid-state quantum dots embedded multi-junction solar cell with the device structure of (Glass/ITO/ZnTe/ZnS/CdS/Au) is achieved to boost the photo-conversion efficiency by incorporating inner layer of ZnS and by effectively utilizing the entire solar spectrum. Electron beam evaporation was used to deposit the three semiconductor materials ZnTe, ZnS and CdS thin films. The optical properties and energy bandgap of each of the three materials were determined using ellipsometric measurements. The device performance was investigated using current voltage (J–V) techniques at room temperature and under AM1.5 illumination conditions. In this study, we showed that the optical energy gaps of some nanoscale binary semiconductor compounds from II–VI family exhibit both direct and indirect types of optical energy bandgap and there is a giant increase in their direct values.

Investigation on the properties of Cu 2 ZnSnSe 4 and Cu 2 ZnSn(S,Se) 4 absorber films prepared by magnetron sputtering technique using Zn and ZnS targets in precursor stacks

Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4 absorber films were grown on soda lime glass and Mo-coated soda lime glass substrates by deposition of the precursor films via RF magnetron sputtering method in the stacking orders of Cu/Sn/Zn/Mo/SLG and Cu/Sn/ZnS/Mo/SLG using metallic Zn or binary sulfide ZnS targets and subsequently carrying out of selenization process. It was aimed to find out the effect of Zn or ZnS target types and the small amount of S originated from ZnS target material used in the deposition of precursor films on the structural, morphological, optical, and electrical characteristics of the films to be selenized. XRD and Raman spectroscopy analysis showed that the kesterite CZTSe structure was predominantly formed in both cases where Zn and ZnS targets were used. According to the EDX analysis, S content in the prepared film using ZnS target was only around 1.79 at%. This indicated that a considerable amount of S in the film was driven out during the selenization process. Scanning electron microscopy analysis revealed that ZnS target material contributed to the achievement of the absorber films with larger grain size. It was also determined that the thickness of the interfacial MoSe2 film between the absorber and Mo films decreased by using ZnS target in the precursor film. This was attributed to ZnS layer with a high melting point acting as a barrier layer over Mo film and retarding the diffusion of Se into the Mo film during the selenization process. In addition, the band gap energy values of the Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4 films were found to be 1.18 and 1.28 eV, respectively.

Flexible Color‐Tunable Electroluminescent Devices by Designing Dielectric‐Distinguishing Double‐Stacked Emissive Layers

AbstractIntrinsically flexible alternating current electroluminescent devices have sparked widespread research interest due to their tremendous potential in bioinspired electronics, smart wearables, and human–machine interfaces. In these applications, it is highly desirable to possess real‐time color tunability but this has not been reported yet. Herein, a flexible color‐tunable electroluminescent device composed of simple double‐stacked emissive layers of ZnS phosphors/dielectric polymer composite is developed by an all‐solution processable method. The color tuning capability can be attributed to the dielectric difference between the two emissive layers, leading to the color combination between two independent emissions originating from different ZnS phosphors at varied electric fields. With the rational selection of the dielectric polymer matrices, a wide‐range color tuning from orange to white and to blue can be realized in a single device just by varying the electric field. It also exhibits high mechanical robustness with well‐maintained performance even after 1000 cycles of bending. Similar natural functionalities like camouflage and visual communication can be further reproduced in the artificial color‐tunable system, thereby opening a general and effective avenue for developing smart wearables and soft electronics.

An emerging high performance photovoltaic device with mechanical stability constants of hybrid (HC(NH2)2PbI3) perovskite

Here in, we present the extensive analysis of the parameters associated with structural, electronic, optical and mechanical properties of HC(NH2)2PbI3 or FAPbI3 (FA = Formamidinium) by using full potential linearized augmented plane wave method (FP-LAPW) within framework on the density functional theory. The band structure shows that FAPbI3 has a direct band gap (1.44 eV) at the symmetry point R (0.5, 0.5, 0.5) and are in best agreement with experimental data. The strong hybridization of s orbitals of Pb and p orbitals of I in valance band plays an important role in the structural stability. From the mechanical constants, we have observed that this is ductile in nature and perfect use for photovoltaic applications. Further, FAPbI3 photovoltaic device has been prepared and device parameters have discussed for ZnO, ZnS, ZnSe, ZnTe and CdS buffer layers. The calculated results for FAPbI3 thin layer solar cell show maximum efficiency (20.48% and 20.77%) with ZnS and CdS buffer layers respectively. The proposed results further validate the prospects of methylammonium (MA) free perovskites and it would be persistent and consistent with the flexible substratum. These are the main features of commercialization perovskite solar cells. Thus, promoting the evolution of cubic FAPbI3, for achieving high performance-based optoelectronic devices and will pave a new path in solar cell industry.

Interfacial ZnS passivation for improvement of transparent ZnO/CuI diode characteristics

To fabricate a n-ZnO/p-CuI heterojunction diode with a high rectification ratio at a large junction area, γ-CuI film was spin-coated on ZnO. Since the n-ZnO/p-CuI diode showed a rectification ratio as small as 2.38 × 102, the ZnS interfacial layer was prepared by successive ionic layer adsorption and reaction. By placing a ZnS layer between the n-ZnO/p-CuI, the rectification ratio from the diode increased to 1.71 × 107 at a junction area of 1 cm2. Modification of the valence band offset and the conduction band offset of the n-ZnO/p-CuI junction in the presence of the interfacial ZnS layer may facilitate carrier transport between ZnO and CuI. In addition, it was confirmed that two types of defects (oxygen vacancy and unpaired electron trapped on an oxygen vacancy) were reduced by insertion of an interfacial ZnS layer. A significant improvement in the rectification ratio resulted from the large decrease in the reverse current in the ZnO/CuI diode by a reduced amount of oxygen vacancies. Therefore, the improvement of band alignment with the decrease in the interfacial defects by the introduction of wide bandgap ZnS passivation layer enhanced the electrical characteristics of ZnO/CuI diode.

Simple Synthesis of CuInS2/ZnS Core/Shell Quantum Dots for White Light-Emitting Diodes.

In this study, the CuInS2/ZnS core/shell quantum dots (QDs) were prepared via simple and environmentally friendly solvothermal synthesis and were used as phosphors for white light-emitting diodes (WLEDs). The surface defect of the CuInS2 core QDs were passivated by the ZnS shell by forming CuInS2/ZnS core/shell QDs. By adjusting the Cu/In ratio and the nucleation temperature, the photoluminescence (PL) peak of the CuInS2 QDs was tunable in a range of 651–775 nm. After coating the ZnS layer and modifying oleic acid ligands, the PL quantum yield increased to 85.06%. The CuInS2/ZnS QD powder thermal stability results showed that the PL intensity of the QDs remained 91% at 100°C for 10 min. High color rendering index values (CRI, 90) and correlated color temperature of 4360 K for the efficient WLEDs were fabricated using CuInS2/ZnS QDs and (Ba,Sr)2SiO4:Eu2+ as color converters in combination with a blue GaN light-emitting diode chip.

Smart pH-Regulated Switchable Nanoprobes for Photoelectrochemical Multiplex Detection of Antibiotic Resistance Genes.

Antibiotic resistance, encoded via particular genes, has become a major global health threat and substantial burden on healthcare. Hence, the facile, low-cost, and precise detection of antibiotic resistance genes (ARGs) is crucial in the realm of human health and safety, especially multiplex sensing assays. Here, a smart pH-regulated switchable photoelectrochemical (PEC) bioassay has been created for ultrasensitive detection of two typical subtypes of penicillin resistance genes bla-CTX-M-1 (target 1, labeled as TDNA1) and bla-TEM (target 2, labeled as TDNA2), whereby pH-responsive antimony tartrate (SbT) complex-grafted silica nanospheres are ingeniously adopted as signal DNA1 tags (labeled as SDNA1-SbT@SiO2NSs). The operations of the PEC bioassay depend on the switchable dissociation of the pH-responsive SDNA1-SbT@SiO2NSs complex under the external pH stimuli, thus initiating the pH-regulated release of ions pre-embedded in sandwich-type DNA nanoassemblies. At acidic conditions, the dissociation of SDNA1 tags (ON state) triggers the release of the embedded SbO+. Under alkaline conditions, the dissociation of SDNA1 tags is inhibited (OFF state). The detection of TDNA2 was achieved via DNA hybridization-triggered metal ion release. The unwinding of the introduced hairpin T-Hg2+-T fragment, hybridized with the second anchored signal DNA (SDNA2), ignites the release of Hg2+. The released SbO+ or Hg2+ ions would trigger the formation of Sb2S3/ZnS or HgS/ZnS heterostructure through ion-exchange with the photosensitive ZnS layer, giving rise to the amplified photocurrents and eventually realizing the ultrasensitive detection of penicillin resistance genes subtypes, bla-CTX-M-1 and bla-TEM. The as-fabricated pH-regulated PEC bioassay, smartly integrating the pH-responsive intelligent unit as SDNA tags, pH-regulated release of embedded ions, and the subsequent ion-exchange-based signal amplification strategy, exhibits high sensitivity, specificity, low-cost, and ease of use for multiplex detection of ARGs. It can be successfully used for measuring bla-CTX-M-1 and bla-TEM in real E. coli plasmids, demonstrating great promise for developing a new class of genetic point-of-care devices.

Site- and Spatial-Selective Integration of Non-noble Metal Ions into Quantum Dots for Robust Hydrogen Photogeneration

Summary Artificial photosystems consisting of semiconductor quantum dots (QDs) and non-noble metal ions (e.g., Fe2+, Co2+, Ni2+) show intrinsic advantages in efficient and cost-effective hydrogen (H2) evolution. However, well-controlled integration of these metal ions into ultra-small QDs is a major challenge. Here, we present a two-step strategy to realize site- and spatial-selective integration of earth-abundant Fe2+ ions in CdSe QDs; i.e., CdSe QDs are modified with a thin and anisotropic ZnS shell, and partial Zn2+ ions are selectively substituted by Fe2+ via cation exchange. The anisotropic ZnS layer not only passivates CdSe core but also works as an ideal medium to intimately anchor Fe2+. The multifunctional CdSe/Zn1−xFexS QD exhibits extraordinary activity and stability toward H2 photogeneration. Specifically, more than 880 mL (∼39,300 μmol) H2 gas is produced from 6 mL of aqueous solution during a consecutive 172 h (>1 week) experiment, thus achieving a turnover number of >600,000 per QD.

Boosting the performance of eco-friendly quantum dots-based photoelectrochemical cells via effective surface passivation

Photoelectrochemical (PEC) cells fabricated using environment-friendly colloidal quantum dots (QDs) are promising optoelectronic devices for future practical solar-to-hydrogen conversion. However, the majority of current eco-friendly QDs-based PEC cells exhibited low efficiency mainly due to the charge trapping at QDs’ surface states and interfacial recombination processes in devices. Here, eco-friendly AgInS2 (AIS) QDs-based PEC cells passivated with variable ZnS layers were fabricated and the effects of ZnS surface passivation on corresponding device performance were investigated. It is demonstrated that optimizing the thickness of the ZnS passivation layers can largely suppress the charge trapping/recombination and enhance the electron injection efficiency in the PEC devices, leading to a saturated photocurrent density of ~5.7 mA/cm2 under standard AM 1.5 G solar illumination. Increasing the thickness of ZnS passivation layers can further inhibit the photocorrosion and give rise to higher device stability. These results indicate that ZnS surface passivation is a facile and efficient technique to boost the performance of eco-friendly QDs-based PEC cells.

Molecular dynamics simulations of zinc sulfide deposition on silver sulfide from aqueous solution

Classical molecular dynamics (CMD) simulation has been performed to study the ZnS deposition from aqueous solution on a surface of crystalline Ag2S. The initial configuration of the Ag2S + ZnS + H2O simulated system includes the surface of crystalline Ag2S silver sulfide with H2O molecules above this surface and Zn2+ and S2- ions located between water molecules. In Ag2S + ZnS + H2O system, sulfur ions are adsorbed originally from a solution on Ag2S surface. The part of deposited Zn atoms Zn is under the first deposited layer of S atoms S, and other Zn atoms Zn are located approximately level with surface S atoms. Performed CMD calculation has shown that the dependences of relative number of the deposited sulfur and zinc atoms on the deposition time are symbate, and formation of first surface ZnS layer occurs during deposition about 10 ns.In addition, the analytical model of ZnS deposition on Ag2S surface is proposed. The CMD simulation confirmed the adequacy of this analytical model.

Distinct and enhanced ultraviolet to visible ZnS-porous silicon (PS):p-Si hybrid metal-semiconductor-metal (MSM) photodetector

Present article reports distinct and enhanced ultraviolet to visible light sensing property of metal-semiconductor-metal (MSM) based ZnS-PS:p-Si hybrid heterostructure. PS:p-Si heterostructure is prepared using electrochemical anodization technique by alternate variation of etching current density within the limit of 17.2–22.1 mA cm−2. ZnS (99.99% purity) in powder form is deposited on PS:p-Si surface via thermal evaporation technique under a chamber pressure of 2 × 10−5 m bar. To achieve MSM configuration Au electrode of ∼8 nm and Al electrode of ∼22 nm thickness are successively coated on top of ZnS-PS:p-Si surface using a shadow mask with dimension of 6 × 6 mm. Morphological features of the heterostructure are observed and analysed using cross section FESEM. This gives thickness of the deposited ZnS layer as around ∼110 nm on ∼540 nm thick PS:p-Si structure. These also confirm uniform interface between the two i.e, ZnS and PS:p-Si layers. Cross sectional EDX analysis indicates diffusion of ZnS particles into the PS layer. Optical analysis observed via UV–Visible spectroscopy gives bandgap (obtained through Tauc plot) of the bare ZnS film to be 3.4 eV with 70–90% transparency in the visible region (390–700 nm). Optical reflectance spectrum of the prepared heterostructure shows decreased reflectivity compared to that of the bare PS:p-Si structure which is itself 20–30% less compared to bulk silicon. Spectral response measured for the wavelength range of 200–500 nm gives distinct and enhanced responsivity peak values of ∼0.94 and ∼1.12 AW−1 at 365 nm (UV) and 400 nm (visible) compared to ∼0.5 AW−1 (maximum at 400 nm) of bare PS:p-Si MSM structure for bias voltage of −4 V. The response and recovery times of the heterostructure are found to be 0.54 ± (4.3×10-4) s, 0.38±9.5×10-5 s and 0.50±2.8×10-4 s, 0.35±6.5×10-5 s under UV and visible irradiations.

Achieving desired quality of ZnS buffer layer by optimization using air annealing for solar cell applications

The possibility of maximum transmittance at lower thickness of light transmitting ZnS layer and its optimization by air-annealing as an alternative to hazardous and expensive CdS is reported in this communication in order to achieve better buffer layer for solar cells. Thin films of ZnS were deposited using e-beam evaporation on glass and ITO substrates and subjected to air-annealing followed by characterizations for physical properties. XRD patterns revealed amorphous behavior which transformed into cubic (111) plane with change of substrate and annealing whereas surface topography reveals hill and deep valley like structures. Optimal transmittance of maximum 95% in visible region, direct band gap of 3.38 eV and maximum electrical conductivity were observed for 200°C annealed films. The study refers that films annealed at 200°C are claimed to be suitable for buffer layer applications.

Improvement of Power Conversion Efficiency of Quantum Dot-Sensitized Solar Cells by Doping of Manganese into a ZnS Passivation Layer and Cosensitization of Zinc-Porphyrin on a Modified Graphene Oxide/Nitrogen-Doped TiO2 Photoanode.

It is vital to acquire power conversion efficiencies comparable to other emerging solar cell technologies by making quantum dot-sensitized solar cells (QDSSCs) competitive. In this study, the effect of graphene oxide (GO), nitrogen, manganese, and a porphyrin compound on the performance of QDSSCs based on a TiO2/CdS/ZnS photoanode was investigated. First, adding GO and nitrogen into TiO2 has a conspicuous impact on the cell efficacy. Both these materials reduce the recombination rate and expand the specific surface area of TiO2 as well as dye loading, reinforcing cell efficiency value. The maximum power conversion efficiency of QDSSC with a GO N-doped photoelectrode was 2.52%. Second, by employing Mn2+ (5 and 10 wt %) doping of ZnS, we have succeeded in considerably improving cell performance (from 2.52 to 3.47%). The reason for this could be for the improvement of the passivation layer of ZnS by Mn2+ ions, bringing about to a smaller recombination of photoinjected electrons with either oxidized dye molecules or electrolyte at the surface of titanium dioxide. However, doping of 15 wt % Mn2+ had an opposite effect and somewhat declined the cell performance. Finally, a Zn-porphyrin dye was added to the CdS/ZnS by a cosensitization method, widening the light absorption range to the NIR (near-infrared region) (>700 nm), leading to the higher short-circuit current density (JSC) and cell efficacy. Utilizing an environmentally safe porphyrin compound into the structure of QDSSC has dramatically enhanced the cell efficacy to 4.62%, which is 40% higher than that of the result obtained from the TiO2/CdS/ZnS photoelectrode without porphyrin coating.

Splitting a terahertz surface plasmon polariton beam using Kapton film

It has been experimentally shown that a rigid polyimide Kapton film of submillimeter thickness is sufficiently transparent in the frequency range of 1.2–3 THz and can be used for splitting surface plasmon polaritons (SPPs) propagating along a flat conducting surface. The transmittance T and reflectance R measured for SPPs excited by a free-electron laser radiation ( λ = 130 µ m ) in “gold–ZnS layer–air” flat structures are in good agreement with the results of numerical simulations obtained using the rigorous coupled-wave analysis technique. Transmittance of the SPPs decreases slightly when the layer gets thicker. To minimize the SPP radiative losses emerging due to diffraction of the SPPs on the impedance discontinuity, the Kapton film should be placed normal to the guiding surface and brought in good contact with it (the gap must be less than λ / 2 ). The performed experiments clearly demonstrated Kapton films to be very promising for SPP beam splitting in large-scale terahertz SPP devices.

Influence of annealing temperature of ZnS-coated TiO2 films on the performance of dye-sensitized solar cells

This work deals with ZnS-coated TiO2 films prepared via liquid phase deposition and immersion techniques and then applied as photoanode of dye-sensitized solar cells. The samples underwent annealing treatment at various annealing temperatures. The morphology of TiO2 is nanograss and covered by agglomerate and hexagonal ZnS layer. The anatase crystallite size, absorption peak wavelength and optical reflectance increase with annealing temperature. However, the energy gap decreases with the temperature. The device utilizing the sample annealed at 400 °C performed the highest η of 0.24 % due to this device owns the lowest leak current and the longest carrier lifetime.

Simple trilayer metamaterial absorber associated with Fano-like resonance

A simple metamaterial absorber suitable for fabrication over large areas associated with a Fano like resonance is proposed. The proposed designed of the metamaterial absorber consists of photoresist disk arrays on a silicon substrate followed by the deposition of a tri layer of Au, ZnS and Au on the top of the structure. Due to the tri layer, there is a formation of a cavity between the substrate and gold layer on the top of photoresist disk and a waveguide in the ZnS layer in between the gold layers on the substrate and the ZnS layer itself. The Fano like resonance arises due to the interference of the cavity mode and the guided-mode resonance as well as the Woods anomaly. The cavity mode resonance works as continuum mode whereas the guided mode resonance and Woods anomaly work as discrete modes. The spectral position of the resonance can be tuned by just controlling the thickness of the tri layer instead of the structural size and shape modification of the micro and nano-structures as usually done in conventional metamaterial absorbers. This design can be easily scaled for fabrication over large areas as it separates the structuring and deposition processes and makes them sequential thereby avoiding expensive and complex lift off or etching processes which are usually required for conventional metamaterial processing.

An investigation on the photovoltaic performance of quantum dot solar cells sensitized by CdTe, CdSe and CdS having comparable size

Abstract Quantum dot sensitized solar cells (QDSSC) have been fabricated with CdTe, CdSe and CdS quantum dots (QDs) of nearly similar size as the photosensitizers. The optical and structural characteristics were studied using absorption spectroscopy, XRD and TEM. Efficiency of the fabricated solar cells was found to improve by the incorporation of an additional buffer layer of ZnS. The value of efficiencies for the QDSSCs corresponding to the sensitizers CdTe, CdSe and CdS are 0.22%, 0.25% and 0.20%. After treatment with ZnS using SILAR cycle, an enhacement in the efficiency to 1.41%, 1.98% and 0.94% was noticed for the QDSSC sensitized with CdTe, CdSe and CdS QDs respectively. The differences in efficiencies as well as other photovoltaic parameters for the solar cells have been explained using the differences in effective masses of charge carriers and carrier lifetime in the three different QD samples. CdSe is found to have high adsorption property towards ZnS compared to CdTe or CdS QDs. Also, the ZnS buffer layer acts as a good agent for reducing the back scattering of electrons thereby improving the efficiency of all the three QD solar cells.

Construction of 2D‐ZnS@ZnO Z‐Scheme Heterostructured Nanosheets with a Highly Ordered ZnO Core and Disordered ZnS Shell for Enhancing Photocatalytic Hydrogen Evolution

AbstractHeterostructure and defects in photocatalyst play highly important role in photocatalysis. Formation of 2D‐ZnS@ZnO Z‐scheme heterostructure and introduction of zinc interstitial defects into ZnO were successfully achieved through a facile in‐situ ion‐exchange hydrothermal approach, and the photocatalysts exhibited high photocatalytic activity for hydrogen evolution. The heterointerface between the highly ordered ZnO core and disordered ZnS shell, and the zinc interstitial, facilitate the transfer and separation of charge carriers, resulting in high photocatalytic activity. The 2D‐ZnS@ZnO photocatalyst with a disordered ZnS layer of about 8 nm in thickness exhibited a photocurrent density about 7.2 times than that of ZnO, which is mainly attributed to the facilitative effect on interface transfer and the increased charge density. In addition, the photocatalytic activity can be adjusted via changing the thickness of the disordered ZnS overlayer. This work provides a strategy for the design of the heterointerface photocatalysts combined with defect engineering, through which the photocatalytic activity can be remarkably improved.

ZnS–ZnO Heterostructure Nanorings Grown under a Possible Early Earth Atmosphere

We synthesize ZnS–ZnO heterostructure nanorings at ∼680 °C under carrier gases with various [CO2]/[N2] ratios simulating an anoxic and weakly reduced atmosphere on early Earth. The synthesized nanorings consist of a ZnS–ZnO bilayered stem, ZnO teeth, and ZnS wing-like structures between the teeth and the ZnS layer. O atoms are supplied through the decomposition of CO2 presumably catalyzed by the ZnS surface. The respective growth directions of ZnS and ZnO layers in the stem are [0001] and [011̅1], and ZnO teeth are directed outward from the ring. The nanorings are structurally different from ZnS–ZnO nanorings having inward-directed teeth, which were grown under an oxygen-containing ambient environment. Contrary to the assumption of sulfide dominance including ZnS and MnS while disregarding oxygen-containing minerals such as ZnO on early Earth, we show that ZnS–ZnO nanorings, which are more advantageous in CO2 reduction efficiency, could be formed.