Zn Thin Films Research Articles

Fabrication and Characterization of Flexible CuI-Based Photodetectors on Mica Substrates by a Low-Temperature Solution Process

Both CuI and CuI:Zn semiconductor thin films, along with MSM-structured UV photodetectors, were prepared on flexible mica substrates at low temperature (150 °C) by a wet chemical method. The two CuI-based films exhibited a polycrystalline phase with an optical bandgap energy close to 3.0 eV. Hall effect measurements indicated that the CuI thin film sample had p-type conductivity, while the CuI:Zn thin film sample exhibited n-type conductivity, with the latter showing a higher carrier mobility of 14.78 cm2/Vs compared to 7.67 cm2/Vs for the former. The I-V curves of both types of photodetectors showed asymmetric rectification characteristics with rectification ratios at ±3 V of 5.23 and 14.3 for the CuI and CuI:Zn devices, respectively. Flexible CuI:Zn devices exhibited significantly better sensitivity, responsivity, and specific detectivity than CuI devices both before and after static bending tests. It was found that, while the optoelectronic performance of flexible CuI-based photodetectors degraded under tensile stress during static bending tests, they still exhibited good reproducibility and repeatability in their photoresponses.

Molecular Dynamics Analysis of Multi-Factor Influences on Structural Defects in Deposited Mg-Matrix Zn Atom Films.

Mg metal vascular stents not only have good mechanical support properties but also can be entirely absorbed by the human body as a trace element beneficial to the human body, but because Mg metal is quickly dissolved and absorbed in the human body, magnesium metal alone cannot be ideally used as a vascular stent. Since the dense oxide Zn film formed by Zn contact with oxygen in the air has good anti-corrosion performance, the Zn nanolayer film deposited on the Mg matrix vascular scaffold by magnetron sputtering can effectively inhibit the rapid dissolution of Mg metal. However, there are few studies on the molecular dynamic structural defects of Mg-matrix Zn atomic magnetron sputtering, and the atomic level simulation of Mg-matrix Zn thin-film depositions can comprehensively understand the atomic level structural defects in the deposition process of Zn thin films from a theoretical perspective to further guide experimental research. Based on this, this research first studied and analyzed the atomic layer structure defects, surface morphology, surface roughness, atomic density of different deposited layers, radial distribution function, and residual stress of the thin-film deposition layer of 1500 deposited Zn atoms at the initial deposition stage, during and after deposition under Mg-matrix thermal layer 500K and a deposited velocity 5 Å/ps by molecular dynamics. At the same time, the effects of temperature and deposited velocity of the Mg-matrix thermal layer on the surface morphology, roughness, and biaxial stress of the deposited films were studied.

Influence of Deposition Parameters on Performance of Zn(O,S) Buffer Layer Deposited by Solution-Based Continuous Flow Reactor for CIGS Solar Cells

CdS thin films are commonly used as buffer layers in hetero-junction structured CIGS thin film solar cells. However, the toxicity of Cd has raised concerns regarding environmental safety and alternative materials have been explored. ZnS is a leading candidate to replace Cd, with the presence of Zn(O,S) impurities known to be required for efficient CIGS solar cell fabrication. In this study, we synthesized Zn(O,S) films using a solution-based deposition method combining a continuous flow reactor (CFR) with another solutionbased deposition method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structural and physicochemical properties of the films, confirming the efficacy of the CFR process for depositing Zn(O,S) thin films in a short period of time. We successfully deposited Zn(O,S) thin films using the combined CFR process. Cd-free B:ZnO/Zn(O,S)/CIGS solar cells were fabricated on Mo-coated glass substrates to investigate the effects of experimental parameters, such as deposition time and method, on the performance of the Zn(O,S) buffer layer in the devices.

Vacuum-evaporated PbS:0.03 Zn thin films with varying thicknesses for environmental applications

In this research, we explore how the thickness of PbS-doped Zn thin films made through thermal vacuum evaporation affects their physical properties for environmental applications. Our x-ray diffraction (XRD) examination shows that the films consist of pure crystalline cubic PbS phase. Additionally, the energy-dispersive X-ray spectroscope (EDXS) provides confirmation that the synthesized products are of high purity. PbS films doped with Zn have spherical nanocrystals ranging from 130 nm to 250 nm in size, as observed through field emission (FE)-scanning electron microscopy (FE-SEM) analysis. The thickness of the film layer was found to correlate significantly with an increase in crystallite size and grain size, as validated by both XRD and FE-SEM analyses. The optical energy gap (Eg) of the thin films under examination exhibited variations in relation to their respective thickness. Bandgap energy was found to decrease from 1.66 eV to 1.2 eV as film thickness was increased from 50 nm to 250 nm. The Arrhenius law shows that films with varying thicknesses have thermally activated electrical conductivity and exhibit two conduction mechanisms. After analyzing the photocatalytic decomposition of methylene blue, it was observed that a thicker (PbS)0.97(Zn)0.03 film with a larger grain size demonstrated superior photocatalytic efficiency (92 % after an exposure duration of 180 min). This is due to a smaller band gap and the presence of defect sites, which enhance catalytic reactions. The study presents a framework for researching the controllable structure, thickness, and composition of chalcogenide semiconductor thin films for environmental applications.

Electrodeposited Lithiophilic Zn Thin Film on the Current Collector for Improved Cyclability of Anode-Free Lithium Metal Battery

Anode-free lithium metal batteries (AFMBs) are recently presented as the new generation of Li metal batteries benefiting high gravimetric and volumetric energy densities due to the zero excess lithium. However, poor electrochemical stability and maximum cyclability of around 40-50 cycles due to the zero excess Lithium prevent the AFLMBs to be functional1. Here, lithiophilic electrodeposited Zn thin film on the current collector is reported in order to decrease the lithium nucleation overpotential and improve the plating/stripping process during alloying and dealloying. Moreover, columbic efficiency is increased by applying more zinc coated on the cupper current collector and by providing a more hospitable site for Li nuclei to plate2. Due to the alloy formation of Li-Zn, more conformal Li growth on the current collector is provided and homogeneous Li distribution and smooth morphology are observed by SEM images. The cells in different zinc thin layer coating are cycled with different current densities as well as long-term cycling by galvanostatic cycling charge-discharge cycling. As a result, increasing the thin film thickness up to 1 micron significantly enhances the electrochemical stability of the cells such as higher columbic efficiency and cyclability, lower Li nucleation overpotential. Finally, the Li-ion chemical diffusion coefficients DLi, are evaluated by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) and the results are compared to each other3.References Maddukuri, S. et al. On the challenge of large energy storage by electrochemical devices. Electrochim Acta 354, 136771 (2020).Merso, S. K. et al. An in-situ formed bifunctional layer for suppressing Li dendrite growth and stabilizing the solid electrolyte interphase layer of anode free lithium metal batteries. J Energy Storage 56, 105955 (2022).Xie, J. et al. Determination of Li-ion diffusion coefficient in amorphous Zn and ZnO thin films prepared by radio frequency magnetron sputtering. Thin Solid Films 519, 3373–3377 (2011).

Fabrication of Two-Dimensional Homo-Bimetallic Porphyrin Framework Thin Films for Optimizing Nonlinear Optical Limiting.

Developing efficient metal-organic framework (MOF) optical devices with tunable third-order nonlinear optical (NLO) properties is an important challenge for scientific research and practical application. Herein, 2D monometallic and hetero/homo-bimetallic porphyrin MOF thin films (ZnTCPP(M) M = H2, Fe, Zn) were fabricated using the liquid-phase epitaxial (LPE) layer-by-layer (LBL) method to investigate the metal substitution dependent third-order NLO behavior. The prepared homo-bimetallic ZnTCPP(Zn) thin film exhibited enhanced third-order NLO performance with a higher third-order nonlinear susceptibility of ∼4.21 × 10-7 esu compared to monometallic and hetero-bimetallic counterparts. Additionally, theoretical calculations were performed to complement the experimental findings and revealed that the enhanced NLO effect of the ZnTCPP(Zn) thin film is mainly attributed to the enhanced local excitation. These findings not only provide a comprehensive understanding of the relationship between metal types and the NLO behavior of porphyrin MOF thin films but also offer valuable insights into the design and optimization of NLO devices.

Effect of graphene oxide coatings on the optical properties of pulsed laser deposited ZnO:Zn thin films

Highly c-axis orientated ZnO:Zn thin films were successfully prepared by pulsed laser deposition and coated with graphene oxide (GO) using nebulizer spray coating. The structural, morphological, and optical properties of the films were studied before and after annealing under different conditions to produce reduced GO (rGO). Following deposition on the surface of the ZnO:Zn films, the GO sheets showed non-uniform and defective textures. Heavily crumbled sheets were observed for rGO annealed in Ar, while wrinkled sheets were observed for rGO annealed in Ar/H2. The uncoated ZnO:Zn exhibited ultraviolet emission at ∼390 nm attributed to the recombination of excitons and a broad band in the range 400–600 nm centred at ∼450 nm attributed to zinc interstitials. The blue emission at ∼450 nm of ZnO:Zn was enhanced after coating with GO and/or rGO, which was attributed to the coupling of the light-emitting centres with localized surface plasmon resonances from the GO/rGO sheets. However, it was found that annealing of uncoated films also improved their luminescence intensity. These results showed that rGO/ZnO films may be useful for some optoelectronic or photoluminescence applications requiring ultraviolet and blue/green light.

Experimental manifestation of redox-conductivity in metal-organic frameworks and its implication for semiconductor/insulator switching

Electric conductivity in metal-organic frameworks (MOFs) follows either a band-like or a redox-hopping charge transport mechanism. While conductivity by the band-like mechanism is theoretically and experimentally well established, the field has struggled to experimentally demonstrate redox conductivity that is promoted by the electron hopping mechanism. Such redox conductivity is predicted to maximize at the mid-point potential of the redox-active units in the MOF, and decline rapidly when deviating from this situation. Herein, we present direct experimental evidence for redox conductivity in fluorine-doped tin oxide surface-grown thin films of Zn(pyrazol-NDI) (pyrazol-NDI = 1,4-bis[(3,5-dimethyl)-pyrazol-4-yl]naphthalenediimide). Following Nernstian behavior, the proportion of reduced and oxidized NDI linkers can be adjusted by the applied potential. Through a series of conductivity measurements, it is demonstrated that the MOF exhibits minimal electric resistance at the mid-point potentials of the NDI linker, and conductivity is enhanced by more than 10000-fold compared to that of either the neutral or completely reduced films. The generality of redox conductivity is demonstrated in MOFs with different linkers and secondary building units, and its implication for applications that require switching between insulating and semiconducting regimes is discussed.

Origin of high optical contrast in zinc-zinc oxide electrodeposits for dynamic windows

The control of solar light and heat emission through windows is an important strategy for increasing the energy efficiency of buildings. Reversible Zn electrodeposition has recently emerged as a promising method for constructing electronically tintable robust dynamic windows. In Zn electrodeposits formed from dimethyl sulfoxide (DMSO) electrolytes during device tinting, we observe extraordinary absorption that is in excess of what is predicted by the Beer-Lambert law for a uniform Zn thin film. The charge required to electroplate these films is abnormally low, significantly less than previously reported dynamic windows based on reversible metal electrodeposition, which facilitates the construction of large-area devices that switch uniformly. Finite-difference time-domain (FDTD) simulations are used to investigate the origin of this enhanced absorption, which arises from plasmonic effects among the Zn nanoparticles and ZnO dendrites in the film. The dielectric ZnO dendrites promote absorption via slit-like Zn-dielectric-Zn structures that from hybrid surface plasmon resonance at metal walls. Through these investigations, we provide design principles to construct low-charge and high-contrast metal and metal oxide-based dynamic windows.

Structural and optical properties of smooth radio frequency sputtered XTe (X=Cd, Zn) thin films

Zinc telluride (ZnTe) and cadmium telluride (CdTe) thin films, with smooth surfaces, were prepared by the radio frequency sputtering method. X-ray diffaction patterns revealed the formation of pure cubic phases and allowed the access of the structural properties. The lattice mismash between the two compounds is found to be around 6%.UV–visible spectroscopy showed a significant absorption coefficient within the visible spectrum, accompanied by an energy band gap measuring 1.9 eVfor the ZnTe film and 1.42 eV for the CdTe film. This study may be benificial for using these materials together of separately in photovoltaic and photocatalytic devices.

Preparation and evaluation of Zn(O,S) thin film layer by sulfurization method

In this paper, we propose a method of incorporating sulfur on the ZnO film surface, which can effectively alter the properties of the ZnO. Through sulfurization, a ZnS cubic crystal structure is formed in the ZnO film, with the ZnS peak increasing as the sulfur weight increases. This approach may pave the way for the successful production of Zn(O,S) film which may suit as an alternative buffer layer for CIGS solar cell structure.

Development of n-type Zn(O, S) buffer layer deposited by open-air CVD method for Cu(In, Ga)Se2 solar cells

A Zn(O, S) thin-film is deposited utilizing an open-air CVD method by evaporating zinc-diethyldithiocarbamate, which is a non-vacuum and dry process. In an X-ray diffraction measurement, it is revealed that the films have a wurtzite structure and an [O]/([O] + [S]) ratio of 10%. A bandgap energy of 3.1 eV is estimated from the transmittance and reflectance spectra. By applying the Zn(O, S) as an n-type buffer layer, Cu(In, Ga)Se2 solar cells are fabricated. In the current density–voltage characteristics, distortion is observed at the bias voltages above the open-circuit voltage. It is implied that a large conduction band offset exists at a Zn(O, S)/CIGS interface. A quantum efficiency spectrum in the wavelength region of 380–512 nm is improved compared to a traditional CdS buffer layer. Finally, a 9.2%-efficient CIGS solar cell is demonstrated utilizing the Zn(O, S) buffer layer through an all-dry process.

Controllable and innovative preparation of Zn(O,S) buffer layers for CIGS thin film solar cells

The band gap of CdS (Eg = 2.4 eV) was narrow, which made it unable to transmit short-wave sunlight through the CIGS absorber layer. Zn(O,S) thin film, prepared by doping O into ZnS, had a wider band gap, and the raw material was green and non-toxic, making it suitable as a buffer layer for solar cells. However, CBD-Zn(O,S) usually takes longer than CdS deposition. In this work, By shortening the deposition time through the fast hydrolysis of TAA. Na3NTA was added in the solutions to improve the quality of Zn(O,S) thin films. The effect of Na3NTA concentration on the complex ion contents was investigated. When Na3NTA was added at a concentration of 0.04 M along with TAA (0.04 M), the film had a high T% of 88.6%, Eg of 3.76 eV, and a dense grain distribution. ZnS and ZnO grew at (111) and (100) crystals, respectively. Raman and XPS analyses showed the existence of Zn–S and Zn–O bonds, indicating the high crystalline quality of the Zn(O,S) thin films prepared with CBD. Finally, when the optimal concentrations of ZnSO4, NH4OH, Na3NTA, and TAA were 0.04 M, 0.48 M, 0.04 M, and 0.04 M, respectively, the prepared Zn(O,S) thin films could be used as a cadmium-free buffer layer for solar cells.

A process study of high-quality Zn(O,S) thin-film fabrication for thin-film solar cells

Abstract The Zn(O,S) thin film is considered a most promising candidate for a cadmium-free buffer layer of the Cu(In,Ga)Se2 (CIGS) thin-film solar cell due to its advantages of optical responses in the short-wavelength region and adjustable bandgap. In this paper, the thin-film growth mechanism and process optimization of Zn(O,S) films fabricated using the chemical bath deposition method are systematically investigated. The thickness and quality of Zn(O,S) films were found to be strongly affected by the concentration variation of the precursor chemicals. It was also revealed that different surface morphologies of Zn(O,S) films would appear if the reaction time were changed and, subsequently, the optimum reaction time was defined. The film-growth curve suggested that the growth rate varied linearly with the deposition temperature and some defects appeared when the temperature was too high. In addition, to further improve the film quality, an effective post-treatment approach was proposed and the experimental results showed that the microstructure of the Zn(O,S) thin film was improved by an ammonia etching process followed by an annealing process. For comparison purposes, both Zn(O,S)-based and CdS-based devices were fabricated and characterized. The device with a Zn(O,S)-CIGS solar cell after post-treatment showed near conversion efficiency comparable to that of the device with the CdS-CIGS cell.

Fabrication and characterization of ZnS and ZnSe absorber layers for UV-selective transparent photovoltaics

We have fabricated ZnS, ZnSe and mixed Zn(S,Se) thin film layers for application as solar cell absorbers in ultraviolet (UV)-selective solar cells. We fabricated the thin film layers using a two-step process involving evaporation of the Zn layer followed by an anneal in an H2S and/or H2Se containing atmosphere. A study of the annealing conditions was performed to minimize hole formation in the thin film layer. A mixed Sulfur and Selenium containing layer was also developed in order to reach a 3 eV band gap, such that the layer absorbs all the UV light and leaves the visible light passing through. Next, we tried to increase the conductivity of the layer by adding extrinsic doping elements. Cu was found to increase the conductivity by more than three orders of magnitude, while leaving the transparency of the layer mostly unchanged. Finally, solar cell devices were fabricated using transparent back and front contacts and a NiO buffer layer. We could measure a very small photocurrent of about 100 μA/cm2 and an open circuit voltage of about 500 mV under AM1.5 G illumination.

The Role of Zn Substitution in Improving the Electrical Properties of CuI Thin Films and Optoelectronic Performance of CuI MSM Photodetectors.

Pure CuI and Zn-substituted CuI (CuI:Zn) semiconductor thin films, and metal-semiconductor-metal (MSM) photodetectors were fabricated on glass substrates by a low-temperature solution process. The influence of Zn substitution concentration (0-12 at%) on the microstructural, optical, and electrical characteristics of CuI thin films and its role in improving the optoelectronic performance of CuI MSM photodetectors were investigated in this study. Incorporation of Zn cation dopant into CuI thin films improved the crystallinity and increased the average crystalline size. XPS analysis revealed that the oxidation state of Cu ions in all the CuI-based thin films was +1, and the estimated values of [Cu]/[I] for the CuI:Zn thin films were lower than 0.9. It was found that the native p-type conductivity of polycrystalline CuI thin film was converted to n-type conductivity after the incorporation of Zn ions into CuI nanocrystals, and the electrical resistivity decreased with increases in Zn concentration. A time-resolved photocurrent study indicated that the improvements in the optoelectronic performance of CuI MSM photodetectors were obtained through the substitution of Zn ions, which provided operational stability to the two-terminal optoelectronic device. The 8 at% Zn-substituted CuI photodetectors exhibited the highest response current, responsivity, and EQE, as well as moderate specific detectivity.

(Invited) A Novel Pathway for the Construction of Core–Shell Photocathodes for PEC Applications

Semiconductor hetero-nanostructures are of great interest for practical use. In this presentation, a novel approach to production of CuO|CuFe2O4 core-shell structure by thermal conversion of CuFe Prussian Blue Analogues will be demonstrated. It represents a new family of photocatalysts that can be used as photoelectrodes able to produce hydrogen under broad spectrum of the visible light. The outstanding photoelectrochemical properties of the photocathodes of CuO|CuFe2O4 have been studied with use of combinatory photo-electrochemical instrumental techniques which proved the electrodes were stable over the whole water photolysis run under relatively positive potentials. Their outstanding performance have been explained by coupling of two charge transfer mechanisms occurring in core-shell architectures. Then, the CuO:Zn nanostructures, in which the photoelectrochemical properties were governed by Fermi level pinning of Zn ions would be presented as well. The implementation of Zn ions enlarged the space charge region and triggered electron availability for the photolysis of water which is unusual for p-type semiconductors. Furthermore, the excellent crystallinity, high surface area, and adhesion to the FTO remarkably improved the photocatalytic activity of the CuO:Zn thin film with cathodic photocurrent of 4 mAcm-2 and a quantum efficiency of 35%, making it promising for hydrogen production.

Multifunctional Zn-Doped ITO Sol-Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material.

Undoped and Zn-doped ITO (ITO:Zn) multifunctional thin films were successfully synthesized using the sol–gel and dipping method on three different types of substrates (glass, SiO2/glass, and Si). The effect of Zn doping on the optoelectronic, microstructural, and gas-sensing properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), Raman spectroscopy, Hall effect measurements (HE), and gas testing. The results showed that the optical constants, the transmission, and the carrier numbers were correlated with the substrate type and with the microstructure and the thickness of the films. The Raman study showed the formation of ITO films and the incorporation of Zn in the doped film (ITO:Zn), which was confirmed by EDX analysis. The potential use of the multifunctional sol–gel ITO and ITO:Zn thin films was proven for TCO applications or gas-sensing experiments toward CO2. The Nyquist plots and equivalent circuit for fitting the experimental data were provided. The best electrical response of the sensor in CO2 atmosphere was found at 150 °C, with activation energy of around 0.31 eV.

Effect of interfacial native oxide on the IV characteristics of ZnO/Si(111) heterojunction

n-ZnO/p-Si(111) heterojunctions, with and without interfacial oxide layer, have been fabricated by growing Zn thin films on Si(111) substrate via DC Magnetron sputtering followed by oxidation in air at 800 °C. The specimen with and without interfacial oxide layer is referred to as ZnO/Si_RCA and ZnO/Si_HF respectively. Quality of the thin film has been studied using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Temperature dependent surface (30 °C - 200 °C) and interfacial (30 °C - 150 ۠°C) current-voltage (T-IV) measurements of both specimens have been studied, under ambient conditions. Surface IV characteristics of ZnO/Si_HF shows lower current response compared to ZnO/Si_RCA. This has been attributed to diffusion of carriers across the junction. ZnO/Si_RCA shows a high ideality factor of 18.9 at 30 °C which decreases to 7.4 at 150 °C. ZnO/Si_HF shows a reduced ideality factor of 11.1 at 30 °C which further decreases to 6.6 at 150 °C.

Vanadium trapped by oblique nano-sheets to preserve the anisotropy in Co–V thin films at high temperature

In this study, oriented nano-sheets generated during the growth of cobalt-rich Co–V and Co–Zn thin films induced a large anisotropy in the magnetic and transport properties. The regular nano-sheets were tilted 52–54 deg. with respect to the substrate plane, ≈ 3.0–4.0 nm thick, ≈ 30–100 nm wide, and ≈ 200–300 nm long, with an inter-sheet distance of ≈ 0.9–1.2 nm. In spite of the different microstructures of the two kinds of samples where the Co–V films were amorphous, whereas the Co–Zn films showed a growth of Zn nanocrystals, the oblique nano-sheet morphology conferred noticeable shape anisotropy to both specimens. This anisotropy resulted in an in-plane uniaxial magnetic anisotropy. The changes in the nano-morphology caused by thermal treatments, and hence in their anisotropic properties, were studied. While the Co–V samples retained or increased their magnetic and transport anisotropies, this anisotropic behavior vanished for the annealed Co–Zn films. High resolution transmission electron microscopy, HRTEM, including chemical analysis at the nano-scale, and the dependence of the anisotropic resistance on temperature allowed to establish the nature and the activation energy spectra of the atomic relaxation processes during heating. These processes displayed a single peak at 1.63 eV for the Co–V and two peaks at 1.67 and 2.0 eV for the Co–Zn. These spectra and their singularities were associated to the changes induced in the nano-morphology of the films by thermal treatments. The Co–V films retained their nano-sheet morphology almost up to 500 ºC; the Co–Zn films lost their nano-sheets at 290 ºC. The thermal stability exhibited by the Co–V films makes them useful for applications in ultra high frequency, optical, magnetostrictive and magneto-electric devices.