Transparent Zinc Oxide Research Articles

Multifunctional Silver Nanoparticle Interlayer-Modified ZnO as the Electron-Injection Layer for Efficient Inverted Organic Light-Emitting Diodes.

The insufficient electron injection constitutes the major obstacle to achieving high-performance inverted organic light-emitting diodes (OLEDs). Here, a facile electron-injection architecture featuring a silver nanoparticle (AgNPs) interlayer-modified sol-gel-derived transparent zinc oxide (ZnO) ultrathin film is proposed and demonstrated. The optimized external quantum efficiencies of the developed inverted fluorescent and phosphorescent OLEDs capitalized on our proposed electron-injection structure reached 4.0 and 21.2% at a current density of 20 mA cm-2 and increased by a factor of 1.90 and 2.86 relative to a reference device without the AgNP interlayer, while simultaneously reducing the operational voltage and substantially ameliorating the device efficiency. Detailed analyses reveal that the local surface plasmon resonance emanated from AgNPs plays three meaningful roles simultaneously: suppressing the surface plasmon polariton mode loss, aiding in energy-level alignments, and inducing and reinforcing the local exciton-plasmon coupling electric field. Among these interesting and multifunctional roles, the enhanced local exciton-plasmon coupling electric field dominates the electron injection enhancement and substantial increases the device efficiency. Additionally, the light-scattering effect also helps in recovering the trapped light energy flux and thus improves the device efficiency. The proposed approach and findings provide an alternative path to fabricate high-performance inverted OLEDs and other related organic electronic or optoelectronic devices.

Investigating Zinc Ketoiminates as a New Class of Precursors for Solution Deposition of ZnO Thin Films.

Zinc oxide (ZnO) has been recognized as one of the most promising metal oxide semiconductor material for processing low-cost thin film transistors (TFTs). Within the scope of this work, we demonstrate a simple, stabilizer free and very efficient chemical solution deposition (CSD) route to grow high quality ZnO layers. The identification of a highly soluble zinc ketoiminate precursor that undergoes hydrolysis under ambient conditions with the facile cleavage of the ligands was the key to develop a simple and straightforward process for ZnO thin films under mild process conditions. Upon heat treatment at moderate temperatures, the precursor decomposes cleanly yielding polycrystalline ZnO thin films, which was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composition was investigated employing complementary techniques such as X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) which revealed high purity ZnO layers. The functional properties in terms of transparency and optical band gap were determined by ultraviolet-visible (UV-Vis) spectroscopy. The transparent ZnO semiconductor thin films serve as active channel layer of thin film transistors (TFT) which was demonstrated by spin coating of the precursor. Subsequent curing in ambient air, yields a 10 nm film that is sufficient to fabricate working TFTs test structures.

Enhanced brightness of methylammonium lead tribromide perovskite microcrystal-based green light-emitting diodes by adding hydrophilic polyvinylpyrrolidone with oleic acid-modified ZnO quantum dot electron transporting layer

In designing highly efficient perovskite light-emitting diodes (PeLEDs), the most significant process is to deposit perovskite film without pinholes and vacancies because discontinuous film results in high leakage current. To fabricate a continuous methylammonium lead tribromide (MAPbBr3) film, a hydrophilic polymer, polyvinylpyrrolidone (PVP), was added to the MAPbBr3 precursor solution. Due to the increased wettability of the precursor solution, a full surface coverage of MAPbBr3-PVP composite film without pinholes was produced. Moreover, zinc oxide (ZnO) quantum dot (QD) was synthesized by hydrothermal process in order to use as an electron transporting layer (ETL), and surface modification of QD was performed by oleic acid (OA) molecules in order to increase spatial distribution in the anti-solvent of perovskite. It was found that, due to the reduced agglomeration of QDs during a spin-coating process, a smooth and highly transparent OA-modified ZnO (OA-ZnO) QD layer was obtained. Thus, the PeLED prepared by using MAPbBr3-PVP composite film and OA-ZnO QD layer exhibited an excellent device performance of a maximum luminance of 11095.1 cd m−2 at 6 V and a maximum current efficiency of 6.79 cd A−1 at 4 V. Therefore, it is believed that adding PVP to perovskite materials and using OA-ZnO QD layer as an ETL are effective way to develop perovskite-based high performance LEDs.

Characteristics of transparent indium zinc oxide electrode prepared on poly(ethylene naphthalate) by radio frequency magnetron sputtering for flexible dye-sensitized solar cells

In this study, for the use as a transparent electrode in flexible dye-sensitized solar cells (DSSCs), the indium zinc oxide (IZO) thin films on unheated poly(ethylene naphthalate) (PEN) substrate in pure argon ambient by radio frequency (RF) magnetron sputtering method have been prepared, and their characteristics with respect to RF power were investigated. It has been found that the IZO films on PEN show a dense amorphous structure and the surface microstructure of the films is hardly sensitive to the RF power. The electrical and optical properties of RF magnetron sputtered IZO thin films on PEN are strongly influenced by RF power. At a RF power of 60 W, it is obtained the IZO thin film with the sheet resistance of about 7.65 Ω/sq. and optical transmittance of about 80% at 550 nm wavelength, resulting in the highest value for figure of merit. The flexible DSSC device embedded with the transparent IZO electrode deposited at 60 W shows the high power conversion efficiency, which is the value of 4.7% under simulated air mass 1.5 irradiation.

Multiaxial and Transparent Strain Sensors Based on Synergetically Reinforced and Orthogonally Cracked Hetero‐Nanocrystal Solids

AbstractWearable strain sensors are widely researched as core components in electronic skin. However, their limited capability of detecting only a single axial strain, and their low sensitivity, stability, opacity, and high production costs hinder their use in advanced applications. Herein, multiaxially highly sensitive, optically transparent, chemically stable, and solution‐processed strain sensors are demonstrated. Transparent indium tin oxide and zinc oxide nanocrystals serve as metallic and insulating components in a metal–insulator matrix and as active materials for strain gauges. Synergetic sensitivity‐ and stability‐reinforcing agents are developed using a transparent SU‐8 polymer to enhance the sensitivity and encapsulate the devices, elevating the gauge factor up to over 3000 by blocking the reconnection of cracks caused by the Poisson effect. Cross‐shaped patterns with an orthogonal crack strategy are developed to detect a complex multiaxial strain, efficiently distinguishing strains applied in various directions with high sensitivity and selectivity. Finally, all‐transparent wearable strain sensors with Ag nanowire electrodes are fabricated using an all‐solution process, which effectively measure not only the human motion or emotion, but also the multiaxial strains occurring during human motion in real time. The strategies can provide a pathway to realize cost‐effective and high‐performance wearable sensors for advanced applications such as bio‐integrated devices.

Mechanical performance of indium zinc oxide films deposited on coating-treated PMMA substrates

Three types of primer layers, including polyurethane (PU), acrylic, and silicone coatings, were developed and deposited on the poly(methylmethacrylate) (PMMA) substrates. Amorphous transparent indium zinc oxide (IZO) films deposited by direct current magnetron sputtering at room temperature on primer-treated and untreated PMMA substrates were investigated ex situ in terms of surface morphology, adhesion, nanoindentation and electrical properties. AFM images show that the microstructure of IZO films was determined by the morphology of the primer layers. IZO films deposited on silicone and acrylic-treated PMMA substrates presented the least surface roughness, which proved that the silicone and acrylic primer layers were more effective to get a dense surface. Nano-scratch tests indicated that the adhesion of IZO films deposited on substrate treated by silicone-based primer layers was superior to that on PU-treated and untreated substrate, which can be attributed to the better mechanical matches of the IZO/primer/PMMA system and the large values of hardness of the silicone primer, which can counterbalance the indentation load and prevent the failure of the films.

Structural, morphological, composition and optical properties of undoped zinc oxide thin films prepared by spray pyrolysis method: effect of solution concentrations

The aim of this paper is the study of transparent undoped zinc oxide thin films obtained by spray pyrolysis technique on glass substrates heated at 350 °C from 0.1 to 0.4 mol solution concentrations using zinc acetate dehydrate as precursor. The X-ray diffraction patterns and Raman spectrometry with respect to Urbach energy and wurtzite structure, show that the maximum value of the high frequency intensity E2 and the optimal value of the optical gap are obtained at 0.2 mol concentration. Furthermore, an appropriate transparency is obtained and that makes these films suitable for photovoltaic windows layer cells.

Reduction in connecting resistivity and optical reflection loss at intermediate layer for mechanically stacked multijunction solar cells

Reduction in the connecting resistivity and optical reflection loss at the intermediate region of mechanically stacked multijunction solar cells are discussed. The top and bottom substrates were bonded using an epoxy-type adhesive with dispersed transparent and conductive indium tin oxide (ITO) particles. The connecting resistivity of the intermediate layer was substantially decreased to 0.12 Ω cm2 for the stacked Si substrates with 40 nm surfaces roughened by SF6/Ar plasma irradiation. The optical reflectivity of the stacked GaAs and Si substrates was well decreased by the insertion of 130-nm-thick transparent and conductive indium gallium zinc oxide (IGZO) layers at the interfaces between the semiconductor substrates and the intermediate adhesive. The IGZO layers functioned as antireflection layers and provided high effective absorbance to the bottom Si substrates for light wavelength regions, in which the top GaAs substrate was transparent and the bottom Si substrate was opaque. The effective absorbencies at incident light angles between 0 and 50° ranged from 0.94 to 0.95 for the stacked GaAs and Si structure with IGZO layers, and from 0.80 to 0.82 for the structure without IGZO layers.

Pressure effect on structural and electrical properties of AZO thin films annealed in N2/H2 atmosphere

Transparent and conductive aluminum-doped zinc oxide (AZO) thin films were developed using a sol-gel method and annealed in 95 N2/5 H2 forming gas. The pressure effects of forming gas on the structural and electrical properties, and the underlying mechanisms were investigated. XPS analysis reveals that the fraction of the chemisorbed oxygen in the annealed film in 0.01 MPa 95 N2/5 H2 did not exhibit any apparent change compared to the non-annealed films, while the oxygen vacancy content exhibited a remarkable increase. When pressure goes up to 0.03 MPa, significant changes of both the oxygen vacancy concentration and the chemisorbed oxygen content were observed in the annealed films. At 0.03 MPa, the films displayed a perfect orientation along the c-axis and exhibited the lowest resistivity of 1.6 × 10−3 Ω·cm. Our study shows that it is possible to optimize the oxygen distribution and improve the electrical property of AZO film by adjustment of the forming gas pressure.

Effect of ambient air flow on resistivity uniformity of transparent Ga-doped ZnO film deposited by atmospheric pressure plasma jet

Transparent gallium-doped zinc oxide films were deposited on large area (117 mm × 185 mm) glass substrates by atmospheric pressure plasma jet method, using two different enclosure conditions—with and without side opening boundary. The opening allows gas exchange between the growth ambient and outside atmosphere. The spatial resistivity distribution was apparently influenced by the air flow field. The case with side opening has higher overall non-uniformity, and the film near the opening has the highest resistivity, caused by considerable reduction in carrier concentration (−32%) and mobility (−15%). Computer fluid dynamics simulations show that air was drawn in, through the side opening, from outside atmosphere, resulting in a much higher oxygen mass fraction (+50%) near the opening. As such, the film near the opening was deposited in O-rich conditions. The degradation of electrical conductivity in O-rich conditions cannot be explained by oxygen vacancies. We suggest that it is due to the formation of dopant-defect complex GaZn−VZn (the lowest formation energy) and reduction of hydrogen impurity (reduced hydrogen partial pressure) in O-rich conditions. Therefore, the tool enclosure, gas flow field, and scanning trajectory must be carefully designed to achieve minimum resistivity non-uniformity on large-area substrates.

Effect of doping concentration, solvent proportions and solution aging on the figure of merit of chemically sprayed ZnO:F thin films

Undoped zinc oxide (ZnO) and fluorine doped zinc oxide (ZnO:F) thin films were deposited on sodalime glass substrates by the ultrasonic chemical spray technique. The effect of the relevant deposition variables, namely, doping concentration, solvent proportions and solution aging on the Haacke´s Figure of Merit, φM, of ZnO:F thin films, is reported for the first time. φM was evaluated from the optical and electrical characteristics of the films. A wide range of F/Zn doping from 5 to 90 at%, in the starting solution, was used due to the high volatility of F during the deposition process and the concomitant poor incorporation into the ZnO lattice. In order to have F-doped solutions with high chemical stability, a mix of acetic acid:water:methanol, at different volume proportions, were tested as solvent; nevertheless the φM magnitudes remain unchanged, irrespective of solvent proportions. Regarding solution aging, despite it is a deposition variable that no plays any role in similar wide band gap semiconductor oxides, in the case of ZnO:F films, φM was significantly influenced through the electrical transport properties. Complementary information on structural and morphological characteristics of deposited ZnO:F thin films, for films with high φM, is also reported. From the results, optimization of deposition variables was achieved, as highly conductive and transparent ZnO:F thin films with a maximum, φM = 7.57 × 10−3 (Ω/□)−1, were deposited with a doping concentration of 30 at%, solvent proportion of 50:50:900, and an aging of 37 days. The obtained results show that ZnO:F thin films are potential candidates for transparent conductive oxide applications.

Solution-processed all-oxide solar cell based on electrodeposited Cu2O and ZnMgO by spray pyrolysis

The paper reports on all-solution-processed, all-oxide solar cells, based on an electrodeposited Cu2O absorber. The transparent indium-doped zinc oxide (IZO) contact and buffer layers of zinc oxide or zinc magnesium oxide (Zn1−xMgxO) were fabricated by ultrasonic spray pyrolysis. The cells were completed with graphite paste top contacts. The focus was set on using exclusively environment-friendly and low-cost raw materials, deposited from aqueous solutions without organic solvents. The latter is especially important for spray pyrolysis, where high process temperatures restrict the use of flammable solvents. The developed spray pyrolysis recipes yielded conductive (25 Ω/sq.) and transparent IZO and various compositions of transparent Zn1−xMgxO layers, with a linear dependence of the energy band gap (3.28–3.50 eV) as a function of the Mg content (0–16 mol %), as seen for layers deposited by vacuum-based techniques. Solar cells with a Zn0.88Mg0.12O buffer showed an improved photovoltaic performance compared to cells with ZnO buffer or without buffer, reaching a power conversion efficiency of 0.67% with a short-circuit current density of 3.76 mA/cm2, an open-circuit voltage of 0.34 V and a fill factor of 52.7%. The study correlated the improved cell performance with structural and electronic properties of the heterojunction.

A simple and transparent well-aligned ZnO nanowire array ultraviolet photodetector with high responsivity

Well-aligned zinc oxide (ZnO) nanowire arrays were grown on an interdigital patterned fluorine tin oxide (FTO)-coated glass substrate by a facile chemical bath deposition at low temperature. Morphology, crystalline structure, and optical properties of the ZnO nanowire arrays were analyzed in detail. The results revealed that the ZnO nanowires had wurtzite structure, typically ∼40–60 nm in diameter, and ∼700–800 nm in length, a great number of highly uniform and dense nanowires grew vertically on the substrate to form the well-aligned ZnO nanowire arrays, which had very high optical transmission (>86%) in the visible light region. In addition, the performance of ZnO nanowire arrays ultraviolet (UV) photodetector was systematically examined. The photosensitivity (S), responsivity (R), response and decay time of the photodetector were 703 at +0.2 V, 113 A/W at +5 V, 23 s and 73 s respectively. Also, the photoresponse mechanism of the UV photodetector was illuminated in terms of the oxygen adsorption-photodesorption process.

P-1.14: The Influence of Dual-channel on the Performance of Self-Align Top-Gate IGZO Thin Film Transistors

In this work, fully transparent dual-layer channel self-aligned top-gate amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are fabricated on glass substrates. Dual-layer channel is consist of indium gallium zinc oxide with different partial pressure of oxygen while sputtering. An oxygen-rich IGZO was deposited to control the threshold voltage and an oxygen-poor IGZO was then deposited to modulate device mobility. The device exhibited the excellent performances, including: a field effect mobility of 5.33 cm2/Vs, a suitable threshold voltage of 1.68V, a sub-threshold swing of 0.54V/dec and a high on/off current ratio. Furthermore, the devices also shows great stability under bias stress.

Red/green/blue selective phototransistors with a hybrid structure of quantum-dots and an oxide semiconductor

Color-selective phototransistors have been developed using a hybrid film of quantum-dots (QDs) and an oxide semiconductor. The zinc oxide (ZnO) phototransistor with QDs with a 2.96 eV band gap showed a photocurrent when illuminated by 450 nm light. The device with QDs with a 2.28 eV band gap started to show a photocurrent under 520 nm light, and the device with QDs with a 1.95 eV band gap showed a photocurrent under light with a wavelength of 635 nm. The photocurrent with low-energy photons, such as visible light, originated when small band-gap QDs absorbed and converted visible light into photoelectrons, and the transparent wide band-gap ZnO supplied a conductive channel in the conduction band to allow the photocurrent to flow through the device. Based on those results, we developed a color-selective phototransistor that can separate red, green, and blue light using a hybrid structure of ZnO and multilayer QDs. The device showed photoresponsivity values of 0.032, 0.053, and 0.26 mA/W to red, green, and blue light, respectively, which are different enough to distinguish the color of the visible light. Therefore, we fabricated and characterized a photogating inverter to convert the color of visible light into an electrical voltage signal. Our results show that the hybrid film of ZnO and QDs could be a feasible way to develop a highly transparent, full-color image sensor.

Investigation of Gate-Stacked In-Ga-Zn-O TFTs with Ga-Zn-O Source/Drain Electrodes by Atmospheric Pressure Plasma-Enhanced Chemical Vapor Deposition.

Atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD) was employed for the fabrication of indium gallium zinc oxide thin-film transistors (IGZO TFTs) with high transparent gallium zinc oxide (GZO) source/drain electrodes. The influence of post-deposition annealing (PDA) temperature on GZO source/drain and device performance was studied. Device with a 300 °C annealing demonstrated excellent electrical characteristics with on/off current ratio of 2.13 × 108, saturation mobility of 10 cm2/V-s, and low subthreshold swing of 0.2 V/dec. The gate stacked LaAlO3/ZrO2 of AP-IGZO TFTs with highly transparent and conductive AP-GZO source/drain electrode show excellent gate control ability at a low operating voltage.

Pulsed laser deposited hexagonal wurzite ZnO thin-film nanostructures/nanotextures for nanophotonics applications

The high-quality and transparent thin-film zinc oxide (ZnO) nanostructures/nanotextures deposited on glass and silicon substrates using pulsed laser deposition (PLD) technique are reported. A solid-state, Nd-YAG laser was used for the PLD process. The films were deposited (i) at room temperature of 25°C (as deposited), (ii) at 150°C, (iii) at 300°C, (iv) at 450°C, and (v) at 600°C and annealed in the vacuum chamber. The depositions were also carried out at different laser repetition rates such as 10 and 5 Hz. UV spectroscopy and photoluminescence (PL) spectroscopy were carried out for optical studies. X-ray diffraction studies were carried out for all samples and analyzed the effects of the laser repetition rate, deposition, and annealing temperatures on the structural properties. Field-emission scanning electron microscope images are recorded for the best-structured samples. The electrical parameters were calibrated using the Hall effect measurement system and the IV characterization was performed using a CHI Electrochemical workstation. The deposition temperature has a significant effect on the microstrain and dislocation density of the ZnO thin film and optical phenomena with various electrical parameters, including the electron mobility, conductivity, and magnetoresistance. These promising results are suitable conditions for nanophotonics applications.

Characterization of conductive Al-doped ZnO thin films for plasmonic applications

Highly conductive and transparent Al-doped zinc oxide films were produced by RF magnetron sputtering for plasmonic applications in the infrared region of the spectrum. These films were characterized using Fourier transform infrared spectroscopy, the Hall effect, Rutherford backscattering spectroscopy and spectral data analysis. Analysis of the results shows a carrier concentration of up to 2.6 × 1020 cm−3, as well as transmission over 80% near the plasma frequency where plasmonic properties are expected. The plasma frequency was calculated from the spectroscopy measurements and subsequent data analysis, and was in agreement with the results from the Hall effect measurements and the free electron gas (Drude) model. Based on these results, the Al-doped zinc oxide thin films are well-suited for plasmonic applications in the infrared region.

Structural, Optical and Luminescence Properties of ZnO Thin Films Prepared by Sol-Gel Spin-Coating Method: Effect of Precursor Concentration

Transparent zinc oxide (ZnO) thin films are fabricated by a simple sol-gel spin-coating technique on glass substrates with different solution concentrations (0.3–1.2 M) using zinc acetate dehydrate [Zn(CH3COO)2·2H2O] as precursor and isopropanol and monoethanolamine (MEA) as solvent and stabilizer, respectively. The molar ratio of zinc acetate dehydrate to MEA is 1.0. X-ray diffraction, ultraviolet-visible spectroscopy and photoluminescence spectroscopy are employed to investigate the effect of solution concentration on the structural and optical properties of the ZnO thin films. The obtained results of all thin films are discussed in detail and are compared with other experimental data.

Influence of Aluminum concentration and substrate temperature on the physical characteristics in chemical sprayed ZnO:Al thin films

The continuous interest in the synthesis and properties study of materials has permitted the development of semiconductor oxides. Zinc oxide (ZnO) with hexagonal wurzite structure is a wide band gap n-type semiconductor and interesting material over a wide range. Chemically sprayed aluminium-doped zinc oxide thin films (ZnO:Al) were deposited on soda-lime glass substrates starting from zinc pentanedionate and aluminium pentanedionate. The influence of both the dopant concentration in the starting solution and the substrate temperature on the composition, morphology, and transport properties of the ZnO:Al thin films were studied. The structure of all the ZnO:Al thin films was polycrystalline, and variation in the preferential growth with the aluminium content in the solution was observed: from an initial (002) growth in films with low Al content, switching to a predominance of (101) planes for heavily dopant regime. The crystallite size was found to decrease with doping concentration and range from 33 to 20 nm. First-order Raman scattering from ZnO:Al, all having the wurtzite structure . The assignments of the E2 mode in ZnO:Al differ from previous investigations. The film composition and the dopant concentration were determined by Auger Electron Spectroscopy (AES); these results showed that the films are almost stoichiometric ZnO. The optimum deposition conditions leading to conductive and transparent ZnO:Al thin films were also found. In this way a resistivity of 0.03 Ω-cm with a (002) preferential growth, were obtained in optimized ZnO:Al thin films.