Ag-doped ZnO Thin Films Research Articles

Enhanced performance of Ag-doped ZnO and pure ZnO thin films DSSCs prepared by sol-gel spin coating

ABSTRACTPure and Ag-doped ZnO photoelectrodes were successfully synthesized by sol-gel spin coating and applied in dye-sensitized solar cells (DSSCs). Ag dopant concentration varied from 0 wt% to 17.13 wt% over weight of ZnO. The structural, morphological, and optical properties of thin films are studied by X-ray diffraction, scanning electron microscopy, and UV-vis spectrophotometer, respectively. The reduction in band gap is observed upon doping, and the highest reduction (from 3.28 to 2.65 eV) is achieved at 10.3 wt%. The conversion efficiency of DSSC is also enhanced by 3.57 times with Ag:ZnO (10.3 wt%) than with pure ZnO film.

Morphology controllable flower like nanostructures of Ag doped ZnO thin films and its application as photovoltaic material

Pure and silver doped ZnO thin films were successfully grown on glass substrates by spray pyrolysis technique. The effect of Ag doping different concentration (2, 4, 6 and 8at.%) on the structural, surface morphological, electrical and optical properties of Ag:ZnO thin films were investigated by X-Ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), photoluminescence (PL) and Hall effect measurement respectively. The X-ray pattern results confirmed that the Ag:ZnO thin films were polycrystalline nature with the preferential orientation along (002) plane in wurtzite structure. The SEM image revealed that the surface morphology of the films nano flower shaped grains with Ag doping. The compositional analysis by EDS confirms the presence of Zn, O and Ag. The surface roughness of the films decreases with increase of silver doping concentration was investigated by Atomic force microscopy (AFM). Optical transmittance 85% and a minimum resistivity of 1.23×10−3Ωcm, are achieved for films when Ag doped ZnO with 6at.% and confirm that these films are suitable for transparent conductive oxide (TCO) applications.

Ag Doped ZnO Thin Films Synthesized by Spray Coating Technique for Methylene Blue Photodegradation under UV Irradiation

Silver (Ag) substituted ZnO thin films were successfully deposited onto glass substrates by spray coating technique. Structure, morphology, and optical properties were evaluated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and UV-Vis spectrophotometer, respectively. XRD spectra had polycrystalline wurtzite structure; SEM images showed that thin films had different surface morphology at different Ag doping concentration. From transmittance spectra, thin films transparency decreased as well as band gap energy along with increase of Ag doping concentration. Methylene blue (MB) solution was used as a pollutant in the photodegradation studies. Under UV light irradiation, the optimal Ag doping is 25%, with 83% of the decolorizing efficiencies after 3 h irradiation time and apparent constant (kapp) about 9.69 × 10−3 min−1.

Effect of silver doping on the structural, morphological, optical and electrical properties of sol–gel deposited nanostructured ZnO thin films

In this paper, we report the study of physical and optical properties of undoped and silver-doped zinc oxide (SZO) thin films prepared by sol–gel dip-coating process onto glass substrates. The structural, morphological, optical and electrical properties of the thin films as a function of silver concentration have been investigated using X-Ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), Atomic Force Microscopy (AFM), UV–visible spectrophotometry and four points probe technique. XRD spectra have shown that undoped thin film exhibit (101) orientation while doped ones display a strong c-axis orientation. SEM micrographs and AFM images have revealed that grain sizes and surface roughness decrease with increasing silver concentration. The UV–visible transmittance results show that Ag-doped ZnO thin films exhibit better transparency than undoped ones. A change in the optical bandgap of ZnO thin films is also revealed. The electrical measurements have shown that the resistivity of the thin films decrease with increasing Ag doping. The present results show that ZnO thin films doped with 4at.% Ag have more suitable properties of high transmittance and low resistivity for optoelectronic device applications.

Structural and optical properties of pure and Ag doped ZnO thin films obtained by sol gel spin coating technique

Abstract We have investigated the influence of Ag doping on zinc oxide thin films. Pure and Ag doped, preferentially oriented transparent zinc oxide thin films were prepared by sol gel technique on a glass substrate using diethyl amine as a stabilizer. The X-ray diffraction analysis revealed that the films with hexagonal wurtzite type structure were polycrystalline in nature with a preferred grain orientation in the 101 direction. The crystallite sizes decreased from 34 nm to 27 nm after silver doping. Both photoluminescence and optical transmission measurements showed that the band gap increased after the Ag doping. The structure and optical characterization studies clearly indicated the incorporation of Ag in ZnO. Hence, the observed increase in the optical band gap and decrease in crystallite size can be directly attributed to the effect of Ag ion incorporation into the ZnO lattice.

Optical Properties and Raman Scattering Investigation of Ag Doped ZnO Thin Film Prepared by Two-Step Solution-Based Deposition Method

Mist-atomization deposition method was applied in order to grow ZnO nanoparticles on Au-seeded glass substrates acting as seeded template. Ag doped ZnO thin films were deposited on ZnO seeded templates by solution-immersion method. The influence of Ag doping content on the optical and Raman scattering properties of ZnO films were systematically investigated by UV-Vis transmittance measurement measured by ultra-violet visible spectroscopy (UV-Vis) and Raman scattering spectrum measured by Raman spectroscopy under room temperature. From UV-Vis transmittance measurement, the incorporation of Ag dopant to the ZnO makes the transmittance wavelength shifted to the shorter wavelength as compared to the pure ZnO. From Raman spectra, 4 cm-1 downshift is observed in Ag-doped thin films as compared to pure ZnO thin films. This Raman peak shift shows that a tensile stress existed in the Ag-doped ZnO film.

Some physical investigations on silver-doped ZnO sprayed thin films

The spray chemical route is used to prepare undoped and Ag-doped ZnO thin films using zinc acetate dehydrate isopropyl alcohol and silver nitrate as doping element in starting solution. XRD analysis shows that all films crystallize in a hexagonal würtzite structure with a preferential orientation along (002) direction. Similarly, the variation in peak positions of X-ray diffraction shows that the silver element is well incorporated into ZnO matrix and not remains in the interstitial sites. Surface morphology studies showed that an increase in the concentration doping causes an increase in the grain size and the mean square roughness Rq. Finally, the optical analysis via the transmittance and the reflectance measurements reveals that the bandgap energy Eg decreases from 3.29 to 3.25eV in terms of Ag content.

Two different mechanisms on UV emission enhancement in Ag-doped ZnO thin films

Ag-doped ZnO thin films were prepared by a sol–gel method. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis and photoluminescence spectra. The results show that the Ag in the ZnO thin films annealed at 500°C for 1h substitutes for Zn and exists in the form of Ag+ ion (AgZn) while the Ag in the ZnO thin films without a post-annealing mainly exists in the form of simple substance (Ag0). The incorporation of Ag indeed can improve the ultraviolet emission of ZnO thin films and suppress the visible emissions at the same time. However, the mechanisms on the ultraviolet emission enhancement in the annealed and unannealed Ag-doped ZnO thin films are very different. As for the post-annealed Ag-doped ZnO thin films, the UV emission enhancement maybe mainly results from more electron–hole pairs (excitons) due to Ag-doping while for the unannealed Ag-doped ZnO thin films; the UV emission enhancement is attributed to the resonant coupling between exciton emission in ZnO and localized surface plasmon in Ag nanoparticles.

Photocatalytic Properties of ZnO and Ag Doped ZnO Thin Films

Pure ZnO thin films and Ag doped ZnO thin films were prepared on quartz substrates by sol-gel process. Structural features and UV absorption spectrum have been studied by XRD and UV-Vis-Nir scanning spectrophotometer. Taking phenol as pollutants, further study of the effect of different annealing temperature and Ag dopant amount of ZnO films on photocatalytic properties was carried out. The results showed that, the optimal annealing temperature on photocatalytic degradation of phenol in this experiment was 300 °C, the best molar ratio of ZnO and Ag was 30:1, which was better than pure ZnO film greatly. Excellent adhesion, recyclable and efficient degradation Ag doped ZnO thin films were found in this experiment.

UV enhancement in polycrystalline Ag-doped ZnO films deposited by the sol–gel method

Undoped and Ag doped ZnO thin films are deposited by the sol–gel spin coating method. XRD spectra with prominent peaks along (100) (002) (101) show the polycrystalline nature of thin films. The particle size lies between 10 to 28nm as estimated by Debye‐Scherrer method and 10 to 20nm as estimated by WH plot method. Surface topology is studied by atomic force microscopy (AFM). Transmission spectra show that all the films are highly transparent (70–90%) in the visible and IR spectral region and absorption occurs near 370nm. Sharp UV emission at 393nm is observed in photoluminescence spectra of the films along with a broad green emission. Emission intensity of UV peak increases as amount of Ag incorporated into ZnO increases. It is enhanced 7 times by Ag doping in ZnO thin film. The intensity of green peak enhances at higher Ag doping percentage.

Solar photocatalytic activity of sol–gel prepared Ag-doped ZnO thin films

Pure and silver doped ZnO thin films over glass substrate were prepared by sol–gel spin-coating method. Prepared films were calcined at different temperatures. X-ray diffraction and UV–Vis spectroscopy were used to characterize the prepared samples. The photocatalytic activity under solar irradiation of the prepared thin films was tested for the degradation of three azo reactive dyes namely Reactive Red 195, Reactive yellow 145 and Reactive orange 122 as an organic pollutant. 6 wt.% Ag doping ratio showed the highest photocatalytic activity. Various operational parameters such as pH of the solution and initial concentration of the dye have been investigated.

Characteraction of Ag-doped ZnO thin film synthesized by sol–gel method and its using in thin film solar cells

Pure 2% and 4% Ag-doped ZnO thin films have been synthesized on glass substrates by sol–gel method. The structure, morphology and optical properties of the samples have been studied by X-ray diffractometer (XRD), scanning probe microscope, UV–vis spectrophotometer, respectively. The XRD result shows that the pure ZnO has a wurtzite hexagonal structure, no phase segregation is observed. The surface morphology of pure ZnO thin film shows that the grains are growing preferentially along the c-axis orientation perpendicular to the substrates. The transmittance spectra reveal that all samples have high transmittance above 90% in visible region. With Ag doping content increase, a red shift is observed. The performance of Ag-doped ZnO films using in thin film solar cells are simulated. The results show that 4% Ag-doped ZnO thin film can greatly improve the absorption of the cells. Compare to pure ZnO, solar cell's energy conversion efficiency improvement of 2.47% is obtained with 4% Ag doped ZnO thin film.

Highly stable non-polar p-type Ag-doped ZnO thin films grown on r-cut sapphire

Non-polar p-type Ag-doped ZnO thin films were grown on r-cut sapphire substrates by pulsed laser deposition. Films deposited at a substrate temperature above 250°C were shown to be (112¯0) oriented (a-plane) according to X-ray diffraction, and maintained p-type behavior after one year according to Hall-effect measurements. Hole carrier concentrations lie in the range of 3.1×1016–5.3×1017cm−3, mobilities in the range of 0.3–1.5cm2V−1s−1, and resistivities in the range of 43–136Ωcm. Optical transmittance measurements indicate a decrease in band gap of ∼0.07–0.08eV for the p-type films. Characteristic stacking fault features were observed along the (011¯2) plane in the p-type films by transmission electron microscopy.

Enhancement of p-type conduction in Ag-doped ZnO thin films via Mg alloying: The role of oxygen vacancy

ZnO, ZnMgO, Ag-doped ZnO (ZnO:Ag), and Ag-doped ZnMgO (ZnMgO:Ag) thin films have been prepared by pulsed laser deposition. All the films have a preferred orientation with the c-axis perpendicular to the substrates. Hall-effect measurements indicate that the ZnO:Ag film exhibits p-type conduction, but obviously worse than that of the ZnMgO:Ag film. A comparative study of p-type ZnO:Ag and ZnMgO:Ag films using photoluminescence and x-ray photoelectron spectroscopy measurements shows that the enhanced p-type conduction in ZnMgO:Ag film is closely related to the increase of the activation energy of the intrinsic donors and the suppression of charge-compensating oxygen-related defects after Mg incorporation.

Oxidative degradation of acid orange 7 using Ag-doped zinc oxide thin films

Ag-doped ZnO thin films with preferred c-axis orientation along (002) have been prepared by spray pyrolysis technique in aqueous medium on to the corning glass substrates. The effect of Ag-doping on to the photoelectrochemical, structural, morphological, optical, luminescence, electrical and thermal properties has been investigated. XRD and Raman study indicates that the films have hexagonal (wurtzite) crystal structure. The effect of Ag loading on the photocatalytic activity of Ag-doped ZnO in the degradation of azo dye is studied and results are compared with pure ZnO. The results show that the rate of degradation of azo dye over Ag-doped ZnO is much higher as compared to pure ZnO. Ag doping in ZnO is highly effective and can significantly enhance the photocatalytic degradation and mineralization of azo dye. The enhancement of photocatalytic activity of Ag-doped ZnO thin films is mainly due to their smaller crystallite size and capability for reducing the electron–hole pair recombination. Kinetic parameters have been investigated in terms of a first order rate equation. The rate constant (−k) for this heterogeneous photocatalysis is evaluated as a function of the initial concentration of original species. Substantial reduction in azo dye is achieved as analyzed from COD and TOC studies.

Size dependent electron–phonon coupling in N, Li, In, Ga, F and Ag doped ZnO thin films

Polarized micro-Raman measurements are performed to study the phonon modes of N, Li, In, Ga, F and Ag doped ZnO thin films, grown by spray pyrolysis on corning glass substrates. The E2high mode displays a visible asymmetric line shape. The size and dopant dependence onto coupling strength between electron and LO phonon is experimentally estimated.

High quality p-type Ag-doped ZnO thin films achieved under elevated growth temperatures

By correlating the effects of substrate temperature, oxygen pressure and laser energy on the electrical and microstructural properties of Ag-doped ZnO films grown on a sapphire (0001) substrate, p-type conductivity is achieved under various substrate temperatures in the wide range of 250–750 °C. All of the samples were deposited by pulsed-laser deposition under various designed conditions. Hall measurements indicate that the best conductivity is achieved in Ag–ZnO films under a substrate temperature of 500 °C, a partial oxygen pressure of 250–300 mTorr and laser energy between 330 and 345 mJ. The hole-carrier concentration is 2.29 × 1018 cm−3, the resistivity is 0.9 Ω cm and the mobility is 3.03 cm2 V−1 s−1. Transmission-electron microscopy (TEM) studies on the p-type films reveal similar microstructural properties to one another, but different properties to that of the n-type films deposited at the same temperatures with different deposition parameters.

Photocatalytic and antibacterial activities of Ag-doped ZnO thin films prepared by a sol–gel dip-coating method

Silver-doped ZnO thin films with various loadings of Ag in the range of 0–10 mol% were prepared by the sol–gel dip-coating method. All prepared films show X-ray powder diffraction patterns that matched with ZnO in its wurtzite structure. The grain size decreased as the Ag loading increased. The prepared films, under UV blacklight illumination, produced a photocatalytic degradation of methylene blue, rhodamine B and reactive orange solutions. Furthermore, they inhibited the growth of Escherichia coli bacteria under UV blacklight irradiation and to a lesser extent in dark conditions. The photocatalytic and antibacterial activities of the prepared films increased with Ag loading, presumably because Ag enhanced the efficiency of generation of superoxide anion radicals (•O2 −) and hydroxyl radicals (•OH).

Electrical properties and Raman scattering investigation of Ag doped ZnO thin films

Ag-doped ZnO thin films were deposited on quartz glass substrates by a radio-frequency (RF) magnetron sputtering technique at room temperature (RT). The influence of Ag doping content on the electrical and Raman scattering properties of ZnO films were systematically investigated by Hall measurement system and Raman scattering spectrum. Two additional local vibrational modes (LVMs) at 230.0 and 394.5 cm −1 induced by Ag dopant in ZnO:Ag films were observed by Raman analyses at RT, corresponding to Ag atoms located at O sites (LV M Zn−Ag) and Zn sites (LV M Ag−O) in ZnO lattice. Moreover, we further studied the effect of donor Ag O and acceptor Ag Zn defects on the electrical properties of ZnO:Ag films. The results indicate that O-rich condition is preferred to suppress the formation of Ag O defects and enhance Ag Zn defects. The p-type ZnO:Ag film was achieved by properly optimizing the annealing conditions under O-rich condition.

Characterization of Ag Doped P-Type ZnO Thin Films Prepared by Electrostatic-Enhanced Ultrasonic Spray Pyrolysis

In this paper, the structure, electrical and optical properties and stabilities of Ag doped p-type ZnO thin films, prepared by electrostatic-enhanced ultrasonic spray pyrolysis were investigated. XRD and Hall data analyses indicated that the resistivity of 4at. % Ag doped p-type ZnO was low, without Ag2O phase separation. The optical transmission spectra illustrated that optical band gaps decreases with the gradual increase of Ag dopant. Moreover, ZnO: Ag films placed for 10 days still showed p-type, but the optical transmittance decreased, suggesting that AgZn in the ZnO: Ag thin films captured electrons to generate Agi, which reunited to be Ag nano-particles and decreased the optical transmittance of ZnO: Ag.