Transparent Conductive Oxide Thin Films Research Articles

Towards sustainable solar cells: unveiling the latest developments in bio-nano materials for enhanced DSSC efficiency

Abstract Fossil fuels—instrumental in powering the nineteenth-century Industrial Revolution—are now under heightened scrutiny due to environmental concerns and carbon emissions. Consequently, there is a global impetus towards achieving carbon-neutral energy production, with solar energy emerging as a cornerstone in this transition. Over the past three decades, dye-sensitized solar cells (DSSCs) have gained increasing prominence due to their unique advantages. This review elucidates several crucial elements essential to DSSC construction, notably bio-nano materials, prized for their structural flexibility, cost-effectiveness and high molar absorption coefficient. It delves into the intricate relationship between molecular structure and DSSC performance, showcasing significant advancements with light-to-power conversion efficiencies reaching 11%. A comprehensive analysis of the photovoltaic performance of DSSCs utilizing bio-nano-based dyes offers invaluable insights into the state of this rapidly evolving industry. Key components under scrutiny include transparent conductive oxide (TCO) layers, physical techniques for metal oxide deposition onto TCO thin films, diverse dye variants and foundational knowledge of components ripe for growth and enhancement. Moreover, the review outlines the latest breakthroughs in the field, providing glimpses into the current status of prototype DSSCs.

Investigation of electrothermal properties of indium-tin-oxide thin films

Transparent conductive oxide (TCO) thin films are highly sought-after for their unique characteristics of conducting electricity and transmitting visible light, making them ideal conductive coating materials for electronic devices. We carried out a comprehensive analysis of the deposition, optical, electrical, and structural properties of ITO and Ag/ITO thin films on glass substrates in this study. The weight ratio of the deposited metals was 1:10, 2:10, and 4:10[Formula: see text]wt.% (Sn:In) for ITO films and 1:1:10[Formula: see text]wt.% (Ag:Sn:In) for Ag–ITO film. The films were annealed at 300°C using a program controller furnace. We employed infrared cameras to analyze the surface temperature profiles of these thin films under external voltage supply. We also investigated the resistivity behavior of both ITO and Ag–ITO films, analyzing them with regard to Mott’s variable range hopping (VRH) model and the fluctuation-induced tunneling model. Scanning electron microscope images revealed that adding Ag increased the grain size of ITO thin films. The average grain size for ITO thin film was determined as 186[Formula: see text]nm, while it was found to be 270[Formula: see text]nm for Ag–ITO thin film. Furthermore, incorporating Ag into the ITO thin film resulted in a reduction of 21.5% in transmittance over the complete visible range of the electromagnetic spectrum when compared to the ITO thin film without Ag as measured by ultra-visible spectrophotometer. The figure of merit was obtained as [Formula: see text] for ITO and [Formula: see text] for Ag–ITO thin films. However, the resistance of the ITO thin film was calculated to be 9.58[Formula: see text]k[Formula: see text], while that of the Ag–ITO film was found to be 6.99[Formula: see text]k[Formula: see text]. The ITO thin film that included Ag exhibited a lower electrical resistivity due to the larger grain size caused by doped Ag atoms in the structure, leading to less electron scattering at the grain boundaries and a resulting decrease in resistivity as determined by four-point probe system. Thermal imaging camera measurements revealed that the surface temperature of the ITO thin film decreased with the addition of Ag under high voltage application, but not under low voltage. When a voltage of 350[Formula: see text]V and 250[Formula: see text]V was applied to the thin films, the ITO film exhibited a surface temperature of 73.9°C and 50.4°C, whereas under identical conditions, the Ag–ITO film showed a surface temperature of 62°C and 44.1°C, respectively. Furthermore, both films exhibited exponentially increasing surface temperature behavior under a certain voltage, suggesting that they have potential for transparent heaters and high-voltage/low-current applications.

A Comprehensive Investigation of the Mechanical and Tribological Properties of AZO Transparent Conducting Oxide Thin Films Deposited by Medium Frequency Magnetron Sputtering.

This paper presents a detailed analysis of aluminium-doped zinc oxide (AZO) thin films and considers them a promising alternative to indium tin oxide in transparent electrodes. The study focusses on critical properties of AZO, including optical, electrical, and mechanical properties, with potential applications in displays, photovoltaic cells, and protective coatings. The deposited AZO thin films are characterised by excellent optical and electrical parameters, with transparency in the visible light range exceeding 80% and resistivity of 10-3 Ω·cm, which gives a high value of figure of merit of 63. Structural analysis confirms the nanocrystalline nature of as-deposited AZO thin films, featuring hexagonal ZnO, orthorhombic Al2O3, and cubic Al2ZnO4 phases. The study includes nanoindentation measurements, which reveal exceptional hardness (11.4 GPa) and reduced elastic modulus (98 GPa), exceeding typical values reported in the literature, highlighting their protective potential. Abrasion tests have shown extraordinary scratch resistance due to the lack of impact on topography and surface roughness up to 10,000 cycles. This comprehensive study demonstrated that as-deposited AZO thin films are multifunctional materials with exceptional optical, electrical, and mechanical properties. The findings open up possibilities for a variety of applications, especially in protective coatings, where the combination of hardness, scratch resistance, and transparency is both rare and valuable.

Progress in the Synthesis and Application of Transparent Conducting Film of AZO (ZnO:Al).

Due to the excellent performance and low cost of the new aluminum-doped zinc oxide (AZO) film, it is expected to replace the mature indium-doped tin oxide (ITO) film. The research status and progress of AZO transparent conductive films are summarized in this review. Moreover, the structure, optoelectronic properties, and conductive mechanism of AZO thin films are also detailed. The thin films' main preparation processes and the advantages and disadvantages of each process method are mainly discussed, and their application fields are expounded. AZO thin films with multicomponent composite structures are one of the promising development directions in transparent conductive oxide (TCO) thin films. The development of various preparation processes has promoted the production and application of thin films on a broad scale. Finally, some improvement schemes have been proposed to improve the comprehensive performance of the film. The industrialization prospects of the AZO film, as well as its great development potential in the digital world, are discussed.

EFFECTIVE MgO /ALUMINA / ITO NANO HETEROSTRUCTURE AS SMART MATERIAL FOR LIGHT-EMITTING DIODE

Transparent conducting oxides (TCO) offer the uncommon functional combination of being both transparent and electrically conductive. For this reason, this study is concerned with the preparation of the triple heterojunction consisting of magnesium oxide, alumina, and ITO using a pulsed laser deposition method with a laser intensity of 3 J. Alumina bulk pellets in propanol were irradiated (Nd:YAG) at a wavelength of 1064 nm. Laser ablation was performed at a laser intensity of 3 J and deposited on ITO, which was then left to dry for 24 hours. The same method was used to attain magnesium nanoparticles, which were spin-coated on the previous sample and dried in a 500 °C oven for 4 hours. Then the properties of nanoparticles were investigated using X-ray diffraction, UV spectroscopy, and scanning electron microscopy (SEM). The results were obtained by UV and XRD analyses. From SEM images, the average size of the synthesized nanoparticles was determined to be about 25–35 nm. Aluminum oxide, MgO, and ITO are 1-D nanostructured semiconductors that function as transparent conducting oxide thin film while also increasing absorption in the visible spectrum. ITO is identified as an appropriate electrode material for infrared photoelectric devices.

Structural, electrical and optical properties of samarium fluoride doped SnO2 transparent conducting oxide thin films for optoelectronic device applications

In this study, p-type transparent tin oxide (SnO2) based semiconductor thin films were deposited onto glass substrates by sol-gel dip-coating method using samarium-trifluoride (SmF3) as acceptor dopant. The films were prepared by co-doping 2 mol.% of SmF3 into SnO2 (SFTO), followed by annealing temperature at 475 °C. XRD analysis results showed that the films exhibited the tetragonal rutile SnO2 phase. The p-type conductance of the SFTO films were confimed by Hall effect and Seebeck coefficient measurements. Resistivity and mobility of the SmF3 doped SnO2 film is 7.83 × 10–3Wcm and 7.57 cm2 V–1 s–1, respectively, which reduce in comparing with those of un-doped SnO2 film. Carrier concentration is large increase from –9.34 ´ 1018 cm–3 for un-doped- to +1.05 × 1020 cm–3 for SmF3 doped-SnO2 film. The p-type SFTO film showed a high transmittance of 74.3% at 550 nm, with band gap energy of 3.63 eV. Furthermore, a transparent p-SnO2:SmF3/n-ZnO:Al (Al doping level of 2 mol.%) heterojunction was fabricated on alkali-free glass substrates. The I-V curve measurement for the p-n heterojunction diode showed a typical rectifying characteristic with a forward turn-on voltage of 1.55 V. With obtained properties, the p-type SFTO film holds great promise for optoelectronic devices applications.

Effect of Sr-doped on physical and photoluminescence properties of SnO2 transparent conducting oxide thin films

Effect of Sr-doped on physical and photoluminescence properties of SnO2 transparent conducting oxide thin films

Improvement of the uniformity of structural and electrical properties of transparent conductive Al-doped ZnO thin films by inductively coupled plasma-assisted radio frequency magnetron sputtering

Transparent conductive Al-doped Zinc oxide thin films were deposited on glass substrates by conventional radio frequency magnetron sputtering (C-RFMS) and inductively coupled plasma-assisted radio frequency magnetron sputtering (ICP-RFMS) methods. The structural and electrical properties of films were studied as a function of the radial position (r) of the substrate in both methods. A good thickness uniformity was obtained in ICP-RFMS, while a significant decrease in film thickness was observed at r=30mm (erosion zone) in C-RFMS. The c-axis orientation was achieved in all positions in ICP-RFMS, while crystallinity was degraded at r≥25mm in C-RFMS. Low resistivity ρ of the order of 10−4Ωcm was obtained at all positions in ICP-RFMS, while ρ was rapidly increased at r≥30mm in C-RFMS. In ICP-RFMS, high-energy ion bombardment is suppressed due to the modified plasma density profile and lower space potential. As for transparency, the sample prepared at r=0mm in ICP-RFMS showed an average visible transmittance of 81%, higher than that in C-RFMS. Throughout the study, it was demonstrated that ICP-RFMS method was promising to improve the radial distribution of structural, electrical, and optical properties of Al-doped ZnO thin films.

A comparative study on Ga3+, Ti4+, and Bi5+-doped SnO2 transparent conducting oxide thin films deposited by the spin coating method

A comparative study on Ga3+, Ti4+, and Bi5+-doped SnO2 transparent conducting oxide thin films deposited by the spin coating method

Review of the Chosen Methods of Producing Front Contacts to Transparent Conductive Oxides Layers in Photovoltaic Structures

It is well known that PV thin films can be deposited by an extensive range of more or less expensive and complicated techniques (such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), pulsed laser deposition, atomic layer deposition (ALD)). The present paper focuses on TCO layers applied by chosen techniques, including mainly the ALD and CVD methods. Thin layers of transparent conductive oxides constitute a well-known group of materials with unique properties. Oxides such as ZnO, SnO2, and In2O3 are the most significant materials of this type; some of them are discussed in the paper. From the application point of view in the photovoltaic industry, the goal is to apply a method that will provide the highest value of electric charge conductivity while maintaining the minimum value of absorption in the layer and a reduced value of the reflection coefficient. The implementation of significant achievements in the coming decade is for developing guidelines for metallization processes and TCO layers deposited by the ALD method. The work contains chosen engineering processes, including the fabrication of transparent conductive oxides (TCO) thin films applied to silicon substrates by ALD and CVD for application as emitter conductive coatings in photovoltaic structures and the fabrication front metallization of solar cell using different techniques, including among others laser techniques. Moreover, the work also contains predictions about solar cells, which will be among the most prevalent solar cells in mass production using thin- and thick-film technology.

SnO2: Investigation of optical, structural, and electrical properties of transparent conductive oxide thin films prepared by nebulized spray pyrolysis for photovoltaic applications

• Tin based conducting oxide material is prepared using the starting material Tin (II)Chloride. • The molar ratio of the material varies from 0.1 M to 0.5 M by dissolving in isoproponal and a few drops of Hydrochloric Acid (HCl) for fine dissolution. • The material crystallinity and grain size has been improved while the prepared SnO 2 substrates were annealed. • The morphological study reveals that the grain size and stoichiometric of the prepared material increases when the molar concentration increases with annealing temperature. EDX studies authenticate the presence of required elements (Sn = 85.75 % & O = 11.31 %) and after annealing it shows the elimination of unwanted elements. The optical band gap values are increased from 3.71 eV to 3.75 eV for with and without samples due to quantum confinement effect. Hall Effect studies shows that after annealing the resistivity will be decreased in the order of 10 -3 Ω cm. • FTIR analysis was used to compare the bending and stretching vibrations of the functional groups associated with the O-sn-O bond for both annealed and non-annealed samples. In the present investigation, we are focused on the preparation of Tin based conducting oxide material. The starting material used is Tin (II)Chloride. The molar ratio of the material varies from 0.1 M to 0.5 M by dissolving in isoproponal and a few drops of Hydrochloric Acid (HCl) for fine dissolution. The well-clean Micro slides were coated using the Nebulizer Spray Pyrolysis (NSP) process at a deposition temperature of 350 °C ± 10 °C and annealed at 300 °C for three hours. The structural, optical, electrical, thickness, functional, and morphological studies are validated with and without annealing. The material crystallinity and grain size has been improved while the prepared SnO 2 substrates were annealed. The morphological study reveals that the grain size and stoichiometric of the prepared material increases when the molar concentration increases with annealing temperature. EDX studies authenticate the presence of required elements (Sn = 85.75 %& O = 11.31 %) and after annealing it shows the elimination of unwanted elements. FTIR analysis was used to compare the bending and stretching vibrations of the functional groups associated with the O-sn-O bond for both annealed and non-annealed samples. The optical band gap values are increased from 3.71 eV to 3.75 eV for with and without samples due to quantum confinement effect. Hall Effect studies shows that after annealing the resistivity will be decreased in the order of 10 -3 Ω cm.

Structural, electrical, and optical properties of rare-earth Sm3+ doped SnO2 transparent conducting oxide thin films for optoelectronic device applications: Synthesized by the spin coating method

Various concentrations of Sm (1, 2, 3, 4, and 5 at%) doped SnO2 thin films were synthesized by the sol-gel spin coating method and investigated the structural, optical, and electrical properties. According to X-ray diffraction studies, all deposited films exhibited the polycrystalline rutile tetragonal structure. The average crystallite size decreased with Sm doping concentration in SnO2, while the dislocation density and lattice strain values were increased. Both XPS and Raman spectra confirm that Sm3+ enters the host SnO2. The higher average optical transmittance is above 86% in pure SnO2, while Sm: SnO2 films exhibit a decreasing trend with the increase of Sm doping concentration and reached up to 77% in 5 at% Sm: SnO2 film. The optical bandgap energy increased with the increase of Sm doping concentration up to 3 at % Sm: SnO2 film (4.23 eV) which is attributed to the Moss-Burstein (MB) effect and then slightly decreased for 4 at% and 5 at% Sm: SnO2 films. Further, the room temperature sheet resistance and resistivity values were found to decrease with the increase of Sm doping concentration up to 3 at % Sm: SnO2 film then it slightly increased in 4 and 5 at% Sm: SnO2 films. Additionally, the efficiency parameter figure of merit (φ) for all the deposited films was calculated.

Embedded nanopattern for selectively suppressed thermal conductivity and enhanced transparency in a transparent conducting oxide film

Transparent conductive oxide (TCO) thin films are cornerstones in many optoelectronic applications including displays, photovoltaics and touchscreens. In these devices, thin films with simultaneous high optical transparency and electrical conductivity are needed. Ideally, heat generated during normal device operation must ideally be compensated for to achieve optimum functionality. One possible way to address the thermal management problem is adding thermoelectric (TE) properties to TCO films. However, improving TE properties while maintaining optimal electrical conductivity and optical transparency is challenging: thermal and electrical transport properties are deeply intertwined. Here, we demonstrate an approach allowing for independent optimization of optical transparency, electrical conductivity and thermal conductivity. An embedded nanopattern structure is filled with indium tin oxide (ITO) and sandwiched between two ITO layers. The resulting triple-layered structure exhibits reduced thermal conductivity and excellent electrical conductivity. This is made possible by electron channels in the embedded ITO nanopattern that electrically connect top and bottom layers, while at the same time limiting phonon-mediated heat conduction. The filling fraction and thickness of the nanopattern are adjusted to improve optical transmission, achieving transparency higher than bare ITO film. The result is a transparent TCO triple layer film with simultaneous high TCO and thermoelectric figures of merit.

A combinatorial study on ZnO-In2O3-SnO2 system: The effects of different postgrowth annealing conditions on optical and electrical properties

ZnO-In2O3-SnO2 (ZITO) thin film library was produced via the combinatorial approach. The films were deposited using a magnetron sputtering system. Varying ZITO compositions were obtained in a single deposition run by employing a custom-made triangular type of substrate carrier magazine. The effect of various postgrowth annealing atmospheres on the electrical and optical properties of the films were examined. Air, Ar, forming gas (Ar+4 vol% H2), and successive annealing under forming gas + argon atmospheres were studied. Room temperature (RT) deposited films were identified either crystalline or amorphous depending on the location of the substrate on the holder. All these samples exhibited average visible transmittance (Tvis) below 75 % and sheet resistance (RS) higher than 50 Ω/□. Annealing under air atmosphere improved the optical and electrical properties of the films significantly, but not simultaneously for the same composition. Although better optical improvement was achieved by annealing under Ar and increase in electrical conductivity after annealing under forming gas, optimum properties have been obtained with the latter condition. Tvis values above 85 % and RS values below 50 Ω/□ were attained. On the other hand, successive annealing did not provide any advantage in reaching optimal samples when compared to single gas atmosphere annealings. Further, increasing the annealing temperature were found to be beneficial particularly for the conductivity of many compositions. Finally, this study has introduced a systematic approach to produce transparent conductive oxide thin films with reduced indium content that can be suitable for many optoelectronic applications.

Transparent conductive SnO2 thin films via resonant Ta doping

Transparent conductive oxide (TCO) thin films are highly desired as electrodes for modern flat-panel displays and solar cells. Alternative indium-free TCO materials are highly needed, because of the scarcity and the high price of indium. Based on the mechanism of resonant doping, Ta has been identified as an effective dopant for SnO2 to achieve highly conductive and transparent TCO. In this work, we fabricated a series of Ta-doped SnO2 thin films (Sn1−xTaxO2, x = 0.001, 0.01, 0.02, 0.03) with high conductivity and high optical transparency via a low-cost sol-gel spin coating method. The Sn0.98Ta0.02O2 film achieves the highest electrical conductivity of 855 S cm−1 with a carrier concentration of 2.3 × 1020 cm−3 and high mobility of 23 cm2 V−1 s−1. The films exhibit a very high optical transparency of 89.5% in the visible light region. High-resolution X-ray photoemission spectroscopy and optical spectroscopy were combined to gain insights into the electronic structure of the Sn1−xTaxO2 films. The optical bandgaps of the films are increased from 3.96 eV for the undoped SnO2 to 4.24 eV for the Sn0.98Ta0.02O2 film due to the occupation of the bottom of conduction band by free electrons, i.e., the Burstein-Moss effect. Interestingly, a bandgap shrinkage is also directly observed due to the bandgap renormalization arising from many-body interactions. The double guarantee of transparency and conductivity in Sn1−xTaxO2 films and the low-cost growth method provide a new platform for optoelectronic and solar cell applications.

Surface Morphology of Textured Transparent Conductive Oxide Thin Film Seen by Various Probes: Visible Light, X-rays, Electron Scattering and Contact Probe.

Fluorine-doped tin oxide thin films (SnO2:F) are widely used as transparent conductive oxide electrodes in thin-film solar cells because of their appropriate electrical and optical properties. The surface morphology of these films influences their optical properties and therefore plays an important role in the overall efficiencies of the solar cells in which they are implemented. At rough surfaces light is diffusely scattered, extending the optical path of light inside the active layer of the solar cell, which in term improves light absorption and solar cell conversion efficiency. In this work, we investigated the surface morphology of undoped and doped SnO2 thin films and their influence on the optical properties of the films. We have compared and analysed the results obtained by several complementary methods for thin-film surface morphology investigation: atomic force microscopy (AFM), transmission electron microscopy (TEM), and grazing-incidence small-angle X-ray scattering (GISAXS). Based on the AFM and TEM results we propose a theoretical model that reproduces well the GISAXS scattering patterns.

Comparative Studies of Undoped/Al-Doped/In-Doped ZnO Transparent Conducting Oxide Thin Films in Optoelectronic Applications

In this paper, undoped, Al-, and In-doped zinc oxide thin films were deposited. Film growth was performed using the sol–gel technique. The method included (a) preparing homogeneous and stable solutions of zinc acetate 2-hydrate, (b) mixing them with aluminum nitrate and indium acetate in 2-methoxyethanol and 2-aminoethanol solutions with various concentrations, and (c) spin coating them onto transparent glass substrates. After thermal annealing, the films showed a high transparency (80–90%) and good stability. Using typical diagnostic tools, the structural, morphological, optical, and electrical film properties were investigated and linked to the dopant type, and concentrations in view of optoelectronics were investigated.

Structural, electrical, and optical properties of spin-coated Bi:SnO2 transparent conducting oxide thin films

We synthesized different concentrations of Bi (1, 2, 3, 4, and 5 at %) doped SnO2 (Bi:SnO2) thin films using the sol-gel spin coating method. The XRD studies confirmed that all deposited films exhibit polycrystalline tetragonal rutile structure. Raman spectra displayed three fundamental bands at 473, 631, and 774 cm−1, which correspond to the Raman modes Eg, A1g, and B2g. The average transmittance is above 76% for all films. The optical bandgap energy increased from 3.91 eV for pure SnO2 to 4.22 eV for 3 at% Bi:SnO2 film and slightly decreased for 4 and 5 at % Bi:SnO2 films. The sheet resistance (Rsh) and resistivity (ρ) values decreased up to 38.8 Ω/□ and 1.62 × 10−3 Ω-cm, respectively, in 3 at % Bi: SnO2 thin film, and then slightly increased for 4 and 5 at % Bi: SnO2 films.

Nonreciprocal Epsilon-Near-Zero-Dielectric Bilayers: Enhancement of Nonreciprocity from a Nonlinear Transparent Conducting Oxide Thin Film at Epsilon-Near-Zero Frequency

We envision the use of an indium tin oxide (ITO) thin film as part of a bilayered silicon-photonics subwavelength device to boost nonlinearity-assisted all-passive and ultrafast nonreciprocal behavior. Asymmetric $p$-polarized oblique excitation of a mode near the epsilon-near-zero frequency, with a highly confined and enhanced normal electric field component and large absorption, allows one to harness the strong subpicosecond nonlinear response of ITO for the generation of notable nonreciprocal performance in an ultracompact two-port element. Although the results are limited by loss, we find the optimal operational point and the maximum attainable nonreciprocal transmittance ratio of the metasurface versus light intensity---including an apparent upper bound slightly over 2---and we perform exhaustive numerical simulations considering nonlinear processes of both anharmonic and thermal nature that validate our predictions, including steady-state and pulsed-laser excitation.

Deep UV transparent conductive oxide thin films realized through degenerately doped wide-bandgap gallium oxide

Deep UV transparent thin films have recently attracted considerable attention owing to their potential in UV and organic-based optoelectronics. Here, we report the achievement of a deep UV transparent and highly conductive thin film based on Si-doped Ga2O3 (SGO) with high conductivity of 2500 S/cm. The SGO thin films exhibit high transparency over a wide spectrum ranging from visible light to deep UV wavelength and, meanwhile, have a very low work-function of approximately 3.2 eV. A combination of photoemission spectroscopy and theoretical studies reveals that the delocalized conduction band derived from Ga 4s orbitals is responsible for the Ga2O3 films’ high conductivity. Furthermore, Si is shown to act as an efficient shallow donor, yielding high mobility up to approximately 60 cm2/Vs. The superior optoelectronic properties of SGO films make it a promising material for use as electrodes in high-power electronics and deep UV and organic-based optoelectronic devices.