New natively textured surface Al-doped ZnO-TCOs for thin film solar cells via magnetron sputtering

Natively textured surface aluminum doped zinc oxide (ZnO:Al) thin films were directly deposited via pulsed direct current (DC) reactive magnetron sputtering on glass substrates. During the reactive sputtering process, the oxygen gas flow rate was varied from 8.5 sccm to 11.0 sccm. The influences of oxygen flow rate on the structural, electrical and optical properties of naturally textured ZnO:Al TCO thin films with milky surface were investigated in detail. Gradual oxygen growth (GOG) technique was developed in the reactive sputtering process for textured ZnO:Al thin films. The light-scattering ability and optical transmittance of the natively textured ZnO:Al TCO thin films can be improved through gradual oxygen growth method while maintaining a low sheet resistance. Typical natively textured ZnO:Al TCO thin film with crater-like surface exhibits low sheet resistance (R_s ～ 4 Ω), high transmittance (T_a > 85%) in visible optical region and high haze value (12.1%).     

Formation of F-doped ZnO transparent conductive films by sputtering of ZnF2

Fluorine-doped ZnO transparent conductive thin films were successfully deposited on glass substrate by radio frequency magnetron sputtering of ZnF₂. The effects of rapid thermal annealing in vacuum on the optical and electrical properties of fluorine-doped ZnO thin films have been investigated. X-ray diffraction spectra indicate that no fluorine compounds, such as ZnF₂, except ZnO were observed. The specimen annealed at 500 °C has the lowest resistivity of 6.65 × 10^? 4 Ω cm, the highest carrier concentration of 1.95 × 10²¹ cm^? 3, and the highest energy band gap of 3.46 eV. The average transmittance in the visible region of the F-doped ZnO thin films as-deposited and annealed is over 90%.     

Effects of intermediate metal layer on the properties of Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayers deposited on polymer substrate

Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayer films were deposited on polyethersulfone (PES) substrate at room temperature. The multilayer films consisted of intermediate Ag metal layers, top and bottom Ga–Al doped ZnO layer. The multilayer with PES substrate had advantages such as low sheet resistance, high optical transmittance in visible range and stable mechanical properties. From the results, sheet resistances of multilayer showed 9 Ω/sq with 12 nm of Ag metal layer thickness. Average optical transmittance of multilayer film showed 84% in visible range (380–770 nm) with 12 nm of Ag metal layer thickness. Moreover the multilayers showed stable mechanical properties than single-layered Ga–Al doped ZnO sample during the bending test due to the existence of ductile Ag metal layer.     

The low temperature synthesis of Al doped ZnO films on glass and polymer using pulsed co-magnetron sputtering: H2 effect

It has been reported that a small amount of hydrogen in argon plasma induces an increase in the crystallite size of the as-deposited films. In addition, control of the hydrogen partial pressure is expected to improve the carrier mobility by increasing the crystallinity of the film (larger crystal size and lower grain boundary effects). Al doped ZnO (AZO) films were deposited by co-CFUBM (closed field unbalanced magnetron) sputtering. The ultimate aim was to deposit transparent films on a polymer substrate with a low electrical resistivity. Therefore, the structural, optical and electrical properties of AZO films were investigated as a function of the hydrogen partial pressure. A minimum resistivity and maximum transparency of 8 × 10^− 4 Ω cm and 88.1% were obtained, respectively. A critical P_H2 was expected to improve the carrier mobility by increasing the crystallinity of the film. However, above this value, conductivity reduced due to the formations of oxides such as ZnO and Al₂O₃ in the AZO films.     

Effects of substrate parameters on structure and optical properties of ZnO thin films fabricated by pulsed laser deposition

Highly oriented zinc oxide thin films have been grown on quartz, Si (1 1 1) and sapphire substrates by pulsed laser deposition (PLD). The effect of temperature and substrate parameter on structural and optical properties of ZnO thin films has been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectra and PL spectra. The experimental results show that the best crystalline thin films grown on different substrate with hexagonal wurtzite structure were achieved at growth temperature 400–500 °C. The growth temperature of ZnO thin film deposited on Si (1 1 1) substrate is lower than that of sapphire and quartz. The band gaps are increasing from 3.2 to 3.31 eV for ZnO thin film fabricated on quartz substrate at growth temperature from 100 to 600 °C. The crystalline quality and UV emission of ZnO thin film grown on sapphire substrate are significantly higher than those of other ZnO thin films grown on different substrates.     

Influence of Ar/O2 ratio on the properties of transparent conductive ZnO:Ga films prepared by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films with highly (002)-preferred orientation were deposited on glass substrates by DC reactive magnetron sputtering method in Ar + O₂ ambience with different Ar/O₂ ratios. The structural, electrical, and optical properties were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The resistivity and optical transmittance of the ZnO:Ga thin films are of the order of 10^− 4 Ω cm and over 85%, respectively. The lowest electrical resistivity of the film is found to be about 3.58 × 10^− 4 Ω cm. The influences of Ar/O₂ gas ratios on the resistivity, Hall mobility, and carrier concentration were analyzed.     

Preparation of aluminum foil-supported nano-sized ZnO thin films and its photocatalytic degradation to phenol under visible light irradiation

The zinc oxide thin films on aluminum foil have been successfully prepared by sol–gel method with methyl glycol as solvent. The film was characterized by means of XRD, TG, UV–vis, SEM and AFM, which show that the ZnO/Al film is formed by a layer of ZnO nano-sized particles with average diameter of 52.2 nm. Under the initial concentration of 20 mg/L phenol solution (500 mL) and visible light irradiation time of 3 h, more than 40% of the initial phenol was totally mineralized using two pieces of ZnO/Al thin film as photocatalyst with an efficient irradiation area of 400 cm². It is a promising visible light responded photocatalyst for the activation of O₂ at room temperature to degrade organic pollutants.     

Influence of the molar concentration and substrate temperature on fluorine-doped zinc oxide thin films chemically sprayed

The effect of both the molar concentration of the starting solution and the substrate temperature on the electrical, morphological, structural and optical properties of chemically sprayed fluorine-doped zinc oxide (ZnO:F) thin films deposited on glass substrates is analyzed in this work. All the starting solutions employed were aged for 10 days before the deposition. The results show that as the molar concentration increases, a decrease in the electrical resistivity values is obtained, reaching the minimum resistivity in films ZnO:F deposited from a 0.4 M solution at 500 °C. A further increase in the molar concentration leads to a very slight increase in the resistivity. On the other hand, as the substrate temperature is increased, the resistivity decreases and a tendency towards to minimum value is evidenced; taking the molar concentration as parameter, minimum values are reached at 500 °C. The obtaining of ZnO:F thin films, with a resistivity as low as 7.8 × 10^− 3 Ω cm (sheet resistance of 130 Ω/□ and film thickness of 600 nm) measured in as-deposited films is reported here for the first time. The concurrent effect of the high molar concentration of the starting solution, the substrate temperature values used, and the ageing of the starting solution, which might cause polymerization of the zinc ions with the fluorine species, enhance the electrical properties. The structure of the films is polycrystalline, with a (002) preferential growth. Molar concentration rules the surface morphology as at low concentration an hexagonal and porous structure is developed changing to a uniform compact and small grain size surface in the films deposited with the high molar concentrations.     

Structural and functional properties of ZnO thin films grown on Si substrates by air assisted USP method from non-aqueous solutions at low-temperature

In this work, we deals with the processing and characterization of transparent conducting ZnO thin films on p-type Silicon substrates (1 0 0) by air assisted Ultrasonic Spray Pyrolysis (USP) method. The thin films from different Zn acetate precursor solution concentrations (0.1, 0.2, 0.3 and 0.4 M) were deposited at several temperatures (400, 450 and 500 °C) with thickness from ～100 to ～500 nm. The effects of precursor solution concentration, deposition time and temperature on the structural, morphological, optical, and electrical properties of ZnO films were studied by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV–Vis-NIR spectroscopy, and Hall Effect techniques, respectively. It has been shown that on the ZnO film surface, the preferred orientation, the average crystallite size, the electrical resistivity and the RMS surface roughness depend on the substrate temperature. The grown films have showed a good adhesion and an excellent optical transmission of about 80–95% within the visible range (400–800 nm) and a direct band gap from 3.35 to 3.23 eV with the increase of the substrate temperature and the deposition time. All the PL spectra have exhibited a typical green-yellow emission band. Additionally photovoltaic (PV) activities of n-ZnO/p-Si heterostructures fabricated are investigated.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Room temperature deposition of IZTO transparent anode films for organic light-emitting diodes

This study was to investigate anodic electrode IZTO films deposited by pulsed DC magnetron sputter at room temperature with various oxygen partial pressures onto glass substrate and to analyze the structural, electrical, and optical properties, as well as the relationship between the chemical binding state of the surface and the characteristics of IZTO films. In addition, the prepared IZTO films were used to fabricate the organic light emitting diodes (OLEDs) as an anode layer to study the device performances. The IZTO film deposited at optimal oxygen partial pressure of 2.0% in sputtering process showed the best properties, such as a low electrical resistivity and high optical transmittance of <5.1 × 10^?4 Ω cm and >80% in the visible wavelength of 400–800 nm, respectively. The OLED characteristics with the optimum condition showed good brightness and the lowest turn-on voltage of >10,000 cd/m² and 4.67 V. These results indicate that IZTO films can be a promising candidate as an alternative TCO electrode material for flexible and OLED devices.     

Natively textured surface aluminum-doped zinc oxide transparent conductive layers for thin film solar cells via pulsed direct-current reactive magnetron sputtering

Natively textured surface aluminum-doped zinc oxide (ZnO:Al) layers for thin film solar cells were directly deposited without any surface treatments via pulsed direct-current reactive magnetron sputtering on glass substrates. Such an in-situ texturing method for sputtered ZnO:Al thin films has the advantages of efficiently reducing production costs and dramatically saving time in photovoltaic industrial processing. High purity metallic Zn-Al (purity: 99.999%, Al 2.0 wt.%) target and oxygen (purity: 99.999%) were used as source materials. During the reactive sputtering process, the oxygen gas flow rate was controlled using plasma emission monitoring. The performance of the textured surface ZnO:Al transparent conductive oxides (TCOs) thin films can be modified by changing the number of deposition rounds (i.e. thin-film thicknesses). The initially milky ZnO:Al TCO thin films deposited at a substrate temperature of ~ 553 K exhibit rough crater-like surface morphology with high transparencies (T ~ 80-85% in visible range) and excellent electrical properties (ρ ~ 3.4 × 10^− 4 Ω cm). Finally, the textured-surface ZnO:Al TCO thin films were preliminarily applied in pin-type silicon thin film solar cells.     

Characteristics of Al-doped c-axis orientation ZnO thin films prepared by the sol–gel method

Transparent conducting ZnO thin films doped with Al have been prepared by sol–gel method, which were characterized by X-ray diffraction, atomic force microscopy and ultra-violet spectrometer. The films showed a hexagonal wurtzite structure and high preferential c-axis orientation. The optical transmittance spectra of the films showed the transmittance higher than 85% within the visible wavelength region. A minimum resistivity of 6.2 × 10⁻⁴ Ω cm was obtained for the film doped with 1.5 mol.% Al, preheated at 300 °C for 15 min and post-heated at 530 °C for 1 h.     

Structural,optical and electrical characterization of ZnO:Ga thin films for organic photovoltaic applications

Gallium-doped zinc oxide (ZnO:Ga) films were prepared on glass substrates by RF magnetron sputtering. The effect of growth temperature on microstructure, optical and electrical properties of the films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometer and four-point probe. The results show that all the films are polycrystalline and (002) oriented, and that the growth temperature significantly affects the microstructure and optoelectrical properties of the films. The film deposited at 670 K has the largest grain size of 71.9 nm, the lowest resistivity of 8.3 × 10^? 4 Ω?cm and the highest figure of merit of 2.1 × 10^? 2 Ω^? 1. Furthermore, the optical energy gaps and optical constants were determined by optical characterization methods. The dispersion behavior of the refractive index was also studied using the Sellmeir's dispersion model and the oscillator parameters of the films were obtained.     

Oxygen plasma power dependence on ZnO grown on porous silicon substrates by plasma-assisted molecular beam epitaxy

ZnO thin films were deposited on porous silicon by plasma-assisted molecular beam epitaxy using different radio frequency power settings. Optical emission spectrometry was applied to study the characteristics of the oxygen plasma, and the effects of the radio frequency power on the properties of the ZnO thin films were evaluated by X-ray diffraction, scanning electron microscopy, and photoluminescence. The grain sizes for radio frequency powers of 100, 200, and 300 W were 46, 48, and 62 nm, respectively. In addition, the photoluminescence intensities of the ultraviolet and the visible range increased at 300 W, because the density of the atomic oxygen transitions increased. The quality of the ZnO thin films was enhanced, but the deep-level emission peaks increased with increasing radio frequency power. The structural and optical properties of the ZnO thin films were improved at the radio frequency power of 300 W. Moreover, the optical properties of the ZnO thin films were improved with porous silicon, instead of Si.     

The fabrication and application of ZnO:Al thin films in low-frequency inductively coupled plasma fabricated silicon solar cell

A home-made radio frequency magnetron sputtering is used to systematically study the structural, electrical, and optical properties of aluminum doped zinc oxide (ZnO:Al) thin films. The intensity of the (002) peak exhibits a remarkable enhancement with increasing film thickness. Upon optimization, we achieved low resistivity of 4.2 × 10^− 4 Ω cm and high transmittance of ~ 88% for ZnO:Al films. Based on the present experimental data, the carrier transport mechanism is discussed. It is found that the grain boundary scattering needs to be considered because the mean free path of free carrier is comparable to the grain size. The 80 nm-ZnO:Al thin films are then deposited onto low-frequency inductively coupled plasma fabricated silicon solar cells to assess the effect of ZnO:Al thin films on the performance of the solar cells. Optimized ZnO:Al thin films are identified as transparent and conductive oxide thin film layers.     

Deposition of nanocrystalline ZnO by wire explosion technique and characterization of the films' properties

ZnO films deposited on glass, quartz and Al on silicon mono-crystal Si (100) substrates by using the wire explosion technique were investigated by X-ray diffraction (XRD), UV–VIS spectroscopy, scanning electron (SEM) and atomic force microscopy (AFM) measurements. X-ray diffraction measurements have shown that ZnO films are mainly composed of (100), (002) and (101) orientation crystallites. The post-deposition thermal treatment at 600 °C temperature in air has shown that the composite of Zn/ZnO film was fully oxidized to ZnO film. The XRD spectra of the film deposited in oxygen atmosphere at room temperature present high intensity dominating peak at 2h = 36, 32° corresponding to the (101) ZnO diffraction peak. The small fraction of the film (7%) corresponds to the (002) peak intensity at 2h = 34, 42°. This result indicates the good crystal quality of the film and hexagonal wurtzite-type structure deposited by zinc wire explosion. The optical absorption spectra shows the bands at 374, 373 and 371 nm corresponding to deposition conditions. The SEM analysis shows that ZnO films presented different morphologies from fractal network to porous films depending on deposition conditions. AFM analysis revealed the grain size ranges from 50 nm to 500 nm. The nanoneedles up to 300 nm in length were found as typical structures in the film. It was demonstrated that the wire explosion technique is a feasible method to produce ZnO crystalline thin films and nanostructures.     

Transparent conducting zinc oxide thin film prepared by off-axis rf magnetron sputtering

Highly conducting and transparent ZnO : Al thin films were grown by off-axis rf magnetron sputtering on amorphous silica substrates without any post-deposition annealing. The electrical and optical properties of the films deposited at various substrate temperatures and target to substrate distances were investigated in detail. Optimized ZnO : Al films have conductivity of 2200 S cm^-1 and average transmission in the visible range is higher than 85%. The conductivity and mobility show very little temperature dependence.     

Wide bandgap Mg-doped ZnAlO thin films for optoelectronic applications

Magnesium-doped ZnAlO thin films were grown on quartz substrate by ablating the sintered target with a KrF excimer laser. The effect of growth temperature from 30 °C to 700 °C on structural, optical, and electrical properties has been studied. These films are highly transparent in visible spectrum with average transmittance of 82%. The films grown at low temperature are amorphous while films grown at high temperature are crystalline in nature. These films are highly oriented along (0 0 2) direction. The electrical conductivity, carrier concentration, and electron mobility is found to increase with increase in temperature and then decreases with further increase in temperature. The bandgap is found to vary from 3.86 eV to 4.00 eV for various films.     

Effect of sputtering power on the electrical and optical properties of Ca-doped ZnO thin films sputtered from nanopowders compacted target

In the present work, we have deposited calcium doped zinc oxide thin films by magnetron sputtering technique using nanocrystalline particles elaborated by sol–gel method as a target material. In the first step, the nanoparticles were synthesized by sol–gel method using supercritical drying in ethyl alcohol. The structural properties studied by X-ray diffractometry indicates that Ca doped ZnO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy (TEM) measurements have shown that the synthesized CZO is a nanosized powder. Then, thin films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature. The influence of RF sputtering power on structural, morphological, electrical, and optical properties were investigated. It has been found that all the films deposited were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (0 0 2) crystallographic direction. They have a typical columnar structure and a very smooth surface. The as-deposited films show a high transmittance in the visible range over 85% and low electrical resistivity at room temperature.