Transparent Conducting Oxide Applications Research Articles

Transparent Conductive Titanium and Fluorine Co-doped Zinc Oxide Films.

Aerosol-assisted chemical vapor deposition (AACVD) was used to deposit highly transparent and conductive titanium or fluorine-doped and titanium-fluorine co-doped ZnO thin films on glass substrate at 450 °C. All films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-Vis spectroscopy, scanning electron spectroscopy (SEM), and four-point probe. The films were 600-680 nm thick, crystalline, and highly transparent (80-87 %). The co-doped film consisted of 0.70 at % titanium and 1 at % fluorine, and displayed a charger carrier mobility, charge carrier concentration, and a minimum resistivity of 8.4 cm2 V-1 s-1, 3.97×1020 cm-3, and 1.69×10-3 Ω cm, respectively. A band gap of 3.6 eV was observed for the co-doped film. Compared to the undoped and singly doped films, the co-doped film displayed a notably higher structure morphology (more homogenous grains with well-defined boundaries) suitable for transparent conducting oxide applications.

High-performance p-type V2O3 films by spray pyrolysis for transparent conducting oxide applications.

High-quality epitaxial p-type V2O3 thin films have been synthesized by spray pyrolysis. The films exhibited excellent electrical performance, with measurable mobility and high carrier concentration. The conductivity of the films varied between 115 and 1079 Scm-1 while the optical transparency of the films ranged from 32 to 65% in the visible region. The observed limitations in thinner films' mobility were attributed to the nanosized granular structure and the presence of two preferred growth orientations. The 60nm thick V2O3 film demonstrated a highly competitive transparency-conductivity figure of merit compared to the state-of-the-art.

Development of nanostructured silver layers via colloidal lithography for AZO/Ag/AZO transparent conductive oxide applications

Development of nanostructured silver layers via colloidal lithography for AZO/Ag/AZO transparent conductive oxide applications

Cation-cation co-doped ZnO thin films for transparent conductive oxide applications

This paper presents a recent study on the structural and transparent conductive properties of sol–gel spin-coated ZnO films, focusing on the effects of cation-cation co-doping. The co-doping combinations investigated include (Sn-Ga), (Ga-Co), and (Ga-Mg). All the films exhibit a ZnO hexagonal wurtzite crystal structure with varying crystallite sizes. Interestingly, the films deposited on glass substrates show a high degree of texture along the (002) lattice plane. Among the (Ga-Sn) co-doped ZnO films deposited on glass substrates, the film with 1 at% Sn-Ga co-doping demonstrates the most promising results in terms of both transparency and electrical conductivity. On quartz substrates, the (Ga-Co) co-doped ZnO films with a composition of 3 at% Ga and 1 at% Co exhibit significantly enhanced optical transmittance and high electrical conductivity, making them promising candidates for optoelectronic applications. Furthermore, the (Ga-Mg) co-doping results in improved optical transmittance and high electrical conductivity for the ZnO films deposited on glass substrates with a composition of 1 at% Ga and 3 at% Mg. The observed results on cation-cation co-doped ZnO films represent an exciting and novel advancement in the field of TCO materials. The findings contribute significantly to the ongoing progress and understanding of co-doped ZnO films as efficient TCO materials for various optoelectronic applications.

Recent Progress in Solution Processed Aluminum and co-Doped ZnO for Transparent Conductive Oxide Applications.

With the continuous growth in the optoelectronic industry, the demand for novel and highly efficient materials is also growing. Specifically, the demand for the key component of several optoelectronic devices, i.e., transparent conducting oxides (TCOs), is receiving significant attention. The major reason behind this is the dependence of the current technology on only one material-indium tin oxide (ITO). Even though ITO still remains a highly efficient material, its high cost and the worldwide scarcity of indium creates an urgency for finding an alternative. In this regard, doped zinc oxide (ZnO), in particular, solution-processed aluminum doped ZnO (AZO), is emerging as a leading candidate to replace ITO due to its high abundant and exceptional physical/chemical properties. In this mini review, recent progress in the development of solution-processed AZO is presented. Beside the systematic review of the literature, the solution processable approaches used to synthesize AZO and the effect of aluminum doping content on the functional properties of AZO are also discussed. Moreover, the co-doping strategy (doping of aluminum with other elements) used to further improve the properties of AZO is also discussed and reviewed in this article.

Electrical and Structural Properties of Semi-Polar-ZnO/a-Al2O3 and Polar-ZnO/c-Al2O3 Films: A Comparative Study.

In this work, the properties of ZnO films of 100 nm thickness, grown using atomic layer deposition (ALD) on a-(100) and c-(001) oriented Al2O3 substrate are reported. The films were grown in the same growth conditions and parameters at six different growth temperatures (Tg) ranging from 100 °C to 300 °C. All as-grown and annealed films were found to be polycrystalline, highly (001) oriented for the c-Al2O3 and highly (101) oriented for the a-Al2O3 substrate. The manifestation of semi-polar-(101) and polar (001)-oriented ZnO films on the same substrate provided the opportunity for a comparative study in terms of the influence of polarization on the electrical and structural properties of ZnO films. It was found that the concentration of hydrogen, carbon, and nitrogen impurities in polar (001)-oriented films was considerably higher than in semi-polar (101)-oriented ZnO films. The study showed that when transparent conductive oxide applications were considered, the ZnO layers could be deposited at a temperature of about 160 °C, because, at this growth temperature, the high electrical conductivity was accompanied by surface smoothness in the nanometer scale. On the contrary, semi-polar (101)-oriented films might offer a perspective for obtaining p-type ZnO films, because the concentration of carbon and hydrogen impurities is considerably lower than in polar films.

A review of various single layer, bilayer, and multilayer TCO materials and their applications

Since fabricating the first transparent conductive oxide (TCO) material, several investigations and applications have been reported in such fields as portable and flexible electronics, solar cells and sensors about this material. This wide range of applications is because of the immense potential in this area and the demands for new devices and technologies. TCOs are used in many areas, such as energy generation, energy-saving, and sensors. In this review, various types of single-layer, bilayer and multilayer TCO materials and their optical and electrical properties, various deposition techniques and applications are investigated. It is shown how manipulation of effective parameters such as doping, growth method and temperature can change the electrical and optical properties. This can lead researchers to proper control on TCO fabricated layers to improve them in their desired context.

Modification in the physical properties of nanocrystalline ZnO thin films by Sn/Ni co-doping for transparent conductive oxide applications

In this paper, the modification in the physical properties of spin-coated ZnO thin films upon Sn/Ni co-doping has been presented. All the films possess the hexagonal wurtzite structure of ZnO with varying surface morphologies. Among all the films, the optical transmittance beyond 550 nm wavelength is maximum for the 1 at% Ni-doped ZnO (1NZO) and (1 at% Sn + 1 at% Ni) co-doped ZnO (1T1NZO) films. The optical band gap for the pristine ZnO film is 3.26 eV, which decreases upon doping and co-doping. The PL spectra of the films exhibit the UV emission corresponding to excitonic transitions and the blue and green emissions related to native defects in the ZnO structure. The room-temperature electrical conductivity is found maximum in the 1T1NZO film. The existence of 1T1NZO film with improved optical transmittance and high electrical conductivity supports its use in transparent conductive oxide applications.

Characterization broadband omnidirectional antireflection ITO nanorod films coating

Three-dimensional (3D) nanostructure electrode based on the transparent conductive oxide (TCO) is an alternative and effective approach for increasing the performance of next-generation photovoltaic and optoelectronic devices. In this work, we prepared the vertically aligned indium tin oxide nanorods (ITO-NRs) film on silicon (100) wafer and commercial ITO thin-film coated glass substrate (ITO-TF/glass) by the glancing angle deposition (GLAD) technique. The morphologies of the ITO-NRs films were confirmed by field-emission scanning electron microscope (FE-SEM). The grazing-incident X-ray diffraction (GIXRD) observed that the ITO-NRs were formed as amorphous and nanocrystalline phase. The photoemission spectra revealed the atomic percentage of elements in ITO-NRs, and the work function of the ITO-NRs was found to increase as a function of layer thickness. To simply demonstrate their feasibility in TCO applications, the ITO-NRs films were deposited on ITO-TF/glass. We found that the resistivity of ITO-NRs on ITO-TF/glass was higher than that of a bare ITO-TF/glass substrate, which can explain through the surface recombination loss. Besides, by precisely tunning the layer thickness of ITO-NRs films, the optical transmittance was enhanced at 85.5–90.0% over the broad wavelength in the visible region with omnidirectional AR characteristic which is superior to that in conventional ITO-TF/glass. Our thickness dependence of the ITO-NRs properties discloses promising 3D TCO nanostructure in wide application.

Effect of the triple (Al, Ga, In) doping in ZnO nanostructures on its transmission, conductivity, and stability for TCO applications

We report the effect of simultaneous doping of three elements aluminum (Al), gallium (Ga) and indium (In), in ZnO nanostructures on its transmission, conductivity, and stability. The triply doped ZnO nanostructures have been synthesized using co-precipitation method and the material has been characterized by various techniques. The results are compared with the undoped ZnO as well as ZnO doped with individual elements (i.e., Al/Ga/In). All the samples have been found possessing hexagonal wurtzite structure. The transparency, conductivity as well as stability (when exposed to high temperature and humidity) of the triply doped ZnO are found better than individually doped ZnO. Our results suggest that doping of three elements may give rise to significant improvement in the properties (transmission, conductivity, and stability), as required for transparent conductive oxide (TCO) applications.

Substrate temperature effect on structure and properties of sputtered polycrystalline transparent conducting oxide films of La-doped BaSnO3

Lanthanum doped barium tin oxide (LBSO) film is an impressive alternative for expensive transparent conducting oxides film such as indium tin oxide. The LBSO films are grown on quartz substrate by co-sputtering a barium tin oxide ceramic target and a lanthanum metal target in Ar/O2 plasma at different substrate temperatures ranging from 500 oC to 730 oC keeping all the other parameters constant. The resulting LBSO films are all polycrystalline in nature and their thickness varies from 520-540 nm. UV-visible absorption spectra of the films show blue shift and increasing optical band gap with increasing substrate temperatures. As the substrate temperature arises up to 650 oC, the optical transparency, Hall mobility, carrier concentration and electrical conductivity of the films all increase due to improving film crystallinity, more oxygen vacancies and higher La dopant incorporation. At optimum substrate temperatures at and above 650 oC, the representative values of optical transmittance, mobility, carrier concentration, and resistivity are ~90 %, 21 cm2/V-s, 5.5 x 1019 cm-3 and 3.4 x 10-3 Ω.cm, respectively. This understanding of varying substrate temperature effect on crystal structure, morphology, electrical, and optical properties of thin film can be further utilized to explore various transparent conducting oxide applications.

Facile Synthesis of Highly Conductive Vanadium-Doped NiO Film for Transparent Conductive Oxide

Metal-oxide-based electrodes play a crucial role in various transparent conductive oxide (TCO) applications. Among the p-type materials, nickel oxide is a promising electrically conductive material due to its good stability, large bandgap, and deep valence band. Here, we display pristine and 3 at.%V-doped NiO synthesized by the solvothermal decomposition method. The properties of both the pristine and 3 at.%V:NiO nanoparticles were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Raman spectroscopy, ultraviolet–visible spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). The film properties were characterized by atomic force microscopy (AFM) and a source meter. Our results suggest that incorporation of vanadium into the NiO lattice significantly improves both electrical conductivity and hole extraction. Also, 3 at.%V:NiO exhibits a lower crystalline size when compared to pristine nickel oxide, which maintains the reduction of surface roughness. These results indicate that vanadium is an excellent dopant for NiO.

Performance optimization of transparent and conductive Zn1-xAlxO thin films for opto-electronic devices: An experimental & first-principles investigation

In the present work, a combination of the experimental techniques with first principle density functional theory (DFT) based calculations has been employed to study the performance of the aluminum doped ZnO (AZO) thin films as transparent conducting oxide (TCO) material. The AZO thin films with varying doping concentration (0 wt% to 10 wt%) and having thickness (<100 nm) were deposited on silicon substrate using pulsed laser deposition. Various structural, optical and electrical properties of the films have been explored using a variety of the experimental techniques e.g. X-ray diffraction, X-ray reflectivity, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and current-voltage characteristic measurements. The different physical properties are observed following interesting trends where the characteristics property shows an optimum response at a particular doping concentration (5 wt%). These trends are correlated and explained based on the structural evolution in the nanostructured AZO thin films on varying doping concentration. Moreover, the prepared films are found to be having significantly high transmission and low resistivity making them useful for TCO application. The experimental findings for the Al-doped ZnO are supported by DFT calculations. Overall, our study provides important inputs to control the properties of Al doped ZnO films for their applications in optoelectronic devices.

Enhanced Electrical Mobilities of Laser Annealed Ga Doped ZnO Thin Films.

In this study, Ga-doped ZnO thin films were prepared, and their potential for transparent conducting oxide applications was assessed. To increase the electrical mobility and reduce the resistance of Ga-doped ZnO thin films, CO₂ laser annealing was employed. Recently, the use of transparent conducting oxides (TCOs) have increased, particularly ZnO-based TCOs have been intensively investigated for display applications. To enhance the electrical and optical properties of ZnO thin films, Ga was used as a dopant. First, Ga-doped ZnO thin-film precursors were prepared by the sol-gel method. Subsequently, Ga-doped ZnO thin films were coated on glass substrates by spin coating. Electrical furnace treatment and rapid thermal annealing were employed to obtain and anneal a wurtzite ZnO based structure. The electrical and optical properties of the annealed thin films were optimized by varying the Ga doping concentration. Via Ga doping and optimized laser annealing, the resistivity of the ZnO film could be decreased from 16.32 Ω· cm to 0.45 Ω·cm; notably, the transmittance was similar (85%) in the 380-800 nm range. The transmittance properties of the films are not presented in this paper. Moreover, after an optical CO₂ laser annealing process, the conductivity of the films improved by more than 40 times. Furthermore, the electrical properties (mobility, resistivity, and bulk and sheet concentrations) of the CO₂-laser-annealed Ga-doped ZnO thin films were optimized.

Effect on the reduction of the barrier height in rear-emitter silicon heterojunction solar cells using Ar plasma-treated ITO film

In this study, we investigated the effect of plasma treatment on an indium tin oxide (ITO) film under an ambient Ar atmosphere. The sheet resistance of the plasma-treated ITO film at 250 W (37.6 Ω/sq) was higher than that of the as-deposited ITO film (34 Ω/sq). Plasma treatment was found to decrease the ITO grain size to 21.81 nm, in comparison with the as-deposited ITO (25.49 nm), which resulted in a decrease in the Hall mobility. The work function of the Ar-plasma-treated ITO (WFITO=4.17 eV) was lower than that of the as-deposited ITO film (WFITO = 5.13 eV). This lower work function was attributed to vacancies that formed in the indium and oxygen vacancies in the bonding structure. Rear-emitter silicon heterojunction (SHJ) solar cells fabricated using the plasma-treated ITO film exhibited an open circuit voltage (VOC) of 734 mV, compared to SHJ cells fabricated using the as-deposited ITO film, which showed a VOC of 704 mV. The increase in VOC could be explained by the decrease in the work function, which is related to the reduction in the barrier height between the ITO and a-Si:H (n) of the rear-emitter SHJ solar cells. Furthermore, the performance of the plasma-treated ITO film was verified, with the front surface field layers, using an AFORS-HET simulation. The current density (JSC) and VOC increased to 39.44 mA/cm2 and 736.8 mV, respectively, while maintaining a WFITO of 3.8 eV. Meanwhile, the efficiency was 22.9% at VOC = 721.5 mV and JSC = 38.55 mA/cm2 for WFITO = 4.4 eV. However, an overall enhancement of 23.75% in the cell efficiency was achieved owing to the low work function value of the ITO film. Ar plasma treatment can be used in transparent conducting oxide applications to improve cell efficiency by controlling the barrier height.

Thermal stability study of niobium doped SnO2 thin film for transparent conducting oxide application

Abstract The temperature-dependent electrical property of niobium (Nb) doped SnO2 (NTO) films were investigated for optoelectronic applications. Temperature-dependent electrical properties of the films show two different conduction processes between 200 °C and 450 °C, as calculated by Arrhenius approaches. In the metal oxide system increase in temperature may be possible to reduce oxygen formation energy, this leads to create more oxygen vacancies. The conductivity of NTO film increased up to 250 °C due to thermally generated free carrier concentration. The electrical conductivity decreased beyond 250 °C due to decreased free carrier mobility because of rapid defect formation at higher temperatures. Generally, free carrier collision, charge carrier absorption by native oxygen, and ionized impurity scattering are predominant factors which affect the mobility of free carrier at different temperature ranges. More importantly, the NTO film deposited at 1.5 wt % of Nb doping concentration in SnO2 system shows better optical transmittance and electrical resistivity than other films. The maximum resistivity of 6.45 × 10−4 Ω cm, sheet resistance of 25.94 Ω/□, optical transmittance of 82%, and thermal stability of 250 °C indicates the suitability of NTO thin films for potential applications in optoelectronic devices.

Improved electrical properties of laser annealed In and Ga co-doped ZnO thin films for transparent conducting oxide applications

In this research, dopants with same stoichiometric composition of In and Ga were varied in the range of 1–4 mol% to increase the electrical conductance and optical transmittance. The total sum of 2 mol% of In and Ga co-doped ZnO thin films showed the lowest sheet resistance of 15.9 kΩ/sq. and high transmittance of more than 90% at 380 nm after rapid thermal annealing (RTA) and CO2 laser annealing. Based on scanning electron microscopy images and calculations using the Scherrer formula, the grain sizes were measured and were compared for the increase of In and Ga dopants. The RTA and CO2 laser annealed ZnO thin films co-doped with 2 mol% of In and Ga exhibited a higher energy band gap of 3.29 eV than those of other specimens. The root mean square (RMS) values of the surface roughness were extracted from atomic force microscopy (AFM) images, and the lowest RMS value of 22 nm was obtained for the RTA and CO2 laser annealed ZnO thin films co-doped with 2 mol% of In and Ga. We believe that this increase in the energy band gap is related to the blue shift in the dopant ionization process of In and Ga dopants. And these RTA and CO2 laser annealing can improve the ionization of In and Ga dopants, which is related to the increased energy band gap.

Some physical properties of nanostructured Al doped ZnO thin films synthesized by RF magnetron sputtering at room temperature

In this research, AZO thin films were deposited on glass substrates with 70 W, 100 W and 125 W RF powers at room temperature by RF magnetron sputtering technique. The structural, optical and surface properties of the produced thin films were investigated. According to the obtained results, the investigated thin films had a crystalline structure and they showed high transparency in the visible region. The increase of RF power produced thicker films. Relatively thicker AZO films produced with higher RF power exhibited greater number of interference fringes in the reflectance and transmittance spectra. The refractive index values of the film produced with 125 W RF power were considerably lower than those of the films produced with 70 W and 100 W due to the decreased packing density. The optical energy band gap values of the produced AZO thin films were higher than that of undoped ZnO films. This expansion resulted from the Burstein–Moss effect. However, the band gap energy value as well as the roughness of the film surface decreased like refractive index with an increase in RF power, especially after 100 W. As a result, the values corresponding to the optical and surface properties can be tuned and AZO thin films can be produced by RF magnetron sputtering technique as promising candidates for optoelectronic devices and transparent conductive oxide applications.

Strain Modulated Optoelectronic Properties of CdO Monolayer

We studied the effect of biaxial tensile and compressive strain on the electronic and optical properties using the density function theory. Electronic properties are investigated in terms of the electronic band structure and density of states. CdO monolayer exhibits a direct bandgap ∼ 1.35 eV using a modified Becke–Johnson approximation. The value of bandgap decreases under both biaxial tensile and compressive strains. Moreover, direct to indirect electronic bandgap transition is observed above 8% tensile strain, whereas direct bandgap nature is conserved under compressive strain. The effective mass of an electron is nearly insensitive to strain, whereas hole effective mass shows linear increment with strain and a sudden jump at the electronic transition point of above 8% tensile strain. The noticed low reflectivity in unstrained and compressive strained conditions suggests that the CdO monolayer may be a promising material for transparent conducting oxide applications.

Laser annealing effects on Ga dopants for ZnO thin films for transparent conducting oxide applications

Ga-doped ZnO (GZO) thin films were prepared for transparent conducting oxide (TCO) applications. For the first time, Ga was successfully employed as an n-type dopant in ZnO materials. For the ionization process of the Ga dopant, an optical annealing process with a high energy was employed. The optimized contents of Ga dopants were tested and analyzed for the TCO applications. Additionally, different types of optical annealing processes were employed and tested for device applications. Before the optical annealing process, furnace annealing was performed as a basic process, and then rapid thermal annealing (RTA) or CO2 laser annealing processes were performed alternately or sequentially. In our experiment, we found that the sequence of the optical annealing process was important for the effectiveness of the annealing owing to the differences in the penetration depth of the wave and the applied energy density. We confirmed that a specific sequential combination of the RTA process and the CO2 laser annealing process can yield high-quality transparent conducing oxide thin films. GZO thin films post annealed using a sequential RTA and CO2 laser annealing methods exhibited the lowest conductance and transmittance values. Also, by introduction of Ga dopant, thin film can obtain high thermal and chemical stability due to its low reactivity and strong resistance to oxidation.