Transparent Conducting Oxide Materials Research Articles

Improved electrical contact properties in Indium-free silicon heterojunction solar cells with amorphous SnO2 TCO layers

Silicon heterojunction (SHJ) solar cells are recognized as one of the most efficient architectures in silicon-based photovoltaic devices. However, the reliance on indium (In)-based transparent conductive oxides (TCO) is anticipated to constrain their production capacity due to the critical and economically volatile nature of In. Recently, low-temperature-grown amorphous SnO2 (a-SnO2) films have been explored as an earth-abundant alternative TCO material. In this study, we examine the electrical contact properties of a-SnO2 layers employed as TCO layers in SHJ cells, focusing on their interaction with the underlying carrier selective contact layers. Our findings indicate that a stack of doped amorphous silicon (a-Si:H) and a-SnO2 exhibits relatively high specific contact resistivity, leading to a significant reduction in the device's fill factor. To address this issue, we propose two approaches: the insertion of a thin ZnO-based TCO layer between a-Si:H and a-SnO2, and the use of nanocrystalline silicon layers in place of a-Si:H. Both approaches effectively reduce the contact resistivity, resulting in improvements in fill factor and conversion efficiency comparable to those of benchmark device with In-based TCOs. Based on these findings, we demonstrate a high-efficiency, In-free, SnO2-based SHJ cell.

Al concentration-dependent electrical modulation of Al-doped ZnO thin film using atomic layer deposition

A series of 150-nm-thick Al-doped ZnO (AZO) thin films with various Al doping concentrations were deposited by atomic layer deposition technique to determine their applicability in transparent electronic devices. For incorporation into transparent electrodes, the electrical properties of AZO films must be modulated to minimize the parasitic effect. The results show that AZO thin films with various Al dopant concentrations had different work-functions and electrical contact properties, while the other physical characteristics were not significantly changed. Hence, AZO thin films can be used as transparent conducting oxide materials and are potential alternatives for the currently used indium-tin-oxide (ITO) thin films.

Effects of ALD Deposition Cycles of Al2O3 on the Morphology and Performance of FTO-Based Dye-Sensitized Solar Cells

In dye-sensitized solar cells (DSSCs), materials classified as Transparent Conducting Oxides (TCOs) have the capacity to conduct electricity and transmit light at the same time. Their exceptional blend of optical transparency and electrical conductivity makes them popular choices for transparent electrodes in DSSCs. Fluorine Tin Oxide (FTO) was utilized in this experiment. The optical and electrical characteristics of TCOs may be negatively impacted by their frequent exposure to hostile environments and potential for deterioration. TCOs are coated with passivating layers to increase their performance, stability, and defense against environmental elements including oxygen, moisture, and chemical pollutants. Because of its superior dielectric qualities, strong chemical stability, and suitability with TCO materials, aluminum oxide (Al2O3) was utilized as a passivating layer for the FTO. In this research work, Al2O3 was deposited via atomic layer deposition (ALD) to form thin mesoporous layers as a passivator in the photoanode (working electrode). The work focuses on finding an appropriate thickness of Al2O3 for optimum performance of the dye-sensitized solar cells. The solar simulation and sheet resistance analysis clearly showed 200 cycles of Al2O3 to exhibit an efficiency of 4.31%, which was the most efficient performance. The surface morphology and topography of all samples were discussed and analyzed.

Large Mid‐Infrared Magneto‐Optic Response from Doped Cadmium Oxide at Its Epsilon‐Near‐Zero Frequency

AbstractThe epsilon‐near‐zero (ENZ) frequency regime of transparent conducting oxide materials is known to yield large enhancements in their optical nonlinearity and electro‐optic response. Here, Faraday rotation is investigated in Gd and In‐doped CdO films and it is found that the Verdet constant peaks at values >3 105 deg T−1 m−1 near the ENZ frequency, which is tunable in the wavelength range 2 < λ< 10 µm by varying the doping concentration. These results are among the highest reported to date in the mid‐infrared spectral range and are in good agreement with the Drude model, which confirms that the magneto‐optic response of doped CdO derives from its free carriers. The combination of a tunable Verdet constant, low optical loss compared to other plasmonic materials, and the ability to deposit CdO on Si with no loss in performance make this material a promising platform for integrated magneto‐optic and magnetoplasmonic devices that operate across the mid‐infrared.

Investigation of Optical and Electric Properties of Post-Annealed Graphene: In2O3:ZnO Thin Film

An investigation of the optical and electric properties of post-annealed In2O3:ZnO:Graphene thin films deposited by a thermionic vacuum arc deposition technology was performed. The post-annealed effects were defined by an investigation of the sample’s optical and electric properties. The lowest band gap value of 3.22 eV for the deposited thin film was obtained. Deposited thin films were transparent. The sample AA2 can be used as a transparent conductive oxide material with a resistance of 95 Ω cm−1. Sample AA2 was annealed at 400 °C for 30 min, and sample AA1 was annealed at 150 °C for 15 min. The graphene peaks for the samples were detected using a Fourier transform infrared spectra. The indium and zinc atomic ratios of the sample were approximately 2% and 10%, respectively. As a result, the deposited sample AA2 is a good candidate for use as transparent conductive oxide. Deposited films have high transparency and relatively low resistance. Finally, graphene is a good doping material for semiconductors.

Magneto-optical transport properties of the nanostructured transparent conducting oxides

A comparative study of the optical absorption properties of the nanostructured transparent conducting oxides (TCOs) such as zinc oxide (ZnO), cadmium oxide (CdO), and gallium oxide (Ga2O3) in the presence of a magnetic field B has been performed. The cyclotron resonance absorption power in the TCO materials of the symmetric Pöschl–Teller quantum well (SPTQW) and the full width at half maximum (FWHM) are obtained by applying the operator projection method, the confined phonon model of Huang–Zhu, and the profile technique. Our main results are as follows: The order of the absorption power intensity in these TCOs from strongest to weakest is Ga2O3, ZnO, and CdO, whereas that of the FWHM from largest to smallest is CdO, ZnO, and Ga2O3. This is because the optical phonon frequency in CdO is the smallest, while that in Ga2O3 is the largest. The influences of the magnetic field strength, the thickness, and the temperature on the FWHM in ZnO, CdO, and Ga2O3 become more significant as the phonon is confined. The optical absorption properties of the TCOs are remarkably enhanced due to the confinement of phonon, and those of CdO are the most dominant among the Ga2O3, ZnO, and CdO. The results of our study can provide particular insights for the design of optoelectronic devices.

Indium-free nonmetal and Nb co-doped anatase TiO2 transparent conductive oxide materials for photovoltaic applications: From first-principles calculations to macroscopic simulation

Various researchers have attempted to design indium-free transparent conductive materials. This study first employed density functional theory combined with the Hubbard U parameter to predict the photoelectric properties of nonmetal (B, C, N, F, P, and S) and Nb co-doped anatase TiO2. The results indicate that Ti0.875Nb0.125O1.96875N0.03125, Ti0.9375Nb0.0625O1.96875F0.03125, Ti0.875Nb0.125O1.96875P0.03125 and Ti0.9375Nb0.0625O1.96875S0.03125 possess characteristics of n-type semiconductors with high transmittance, exceptional thermal stability and wide bandgap. Notably, Ti0.9375Nb0.0625O1.96875S0.03125 exhibits optimal electronic conductivity due to its lower effective mass and higher electron concentration. Then, we used the SCAPS-1D solar cell simulation software to simulate the macroscopic characteristics of the MASnI3-based perovskite solar cell with Ti0.9375Nb0.0625O1.96875S0.03125 transparent conductive oxide layer based on the microscopic properties computed at the density functional theory level. A maximum efficiency of 27.17 % is obtained by regulating the thickness, electron affinity, and defect density of Ti0.9375Nb0.0625O1.96875S0.03125 layer and the thickness of MASnI3 absorber layer. The findings highlight the tremendous potential of Ti0.9375Nb0.0625O1.96875S0.03125 as an indium-free transparent conductive oxide candidate material for photovoltaic applications.

Thermal conduction in polycrystalline or amorphous transparent conductive oxide films

With the widespread utilization of transparent conductive oxides (TCO) in various electronic devices, it is beneficial to revisit the fundamentals of heat conduction to formulate a comprehensive physical understanding for thermal properties of TCOs with the aim of improving the thermal design of electronic devices. For degenerate polycrystalline TCO films, both free electrons and phonons act as heat carriers, where free electron contribution can be calculated based on the Wiedemann-Franz law.Interestingly, the phonon thermal conductivity remains almost constant for degenerated polycrystalline TCO films with different dopant concentrations, suggesting the existence of dopant-induced minimum phonon thermal conductivity. For degenerate amorphous TCO film, free electrons act as heat carriers along the conduction path formed by the orbital overlap of cations, which also obey the Wiedemann-Franz law. Moreover, the atomic vibration contribution to thermal conductivity almost keeps unchanged for amorphous TCO films deposited under different conditions, indicating the existence of a minimum thermal conductivity caused by the scattering of vibrational mode due to structural randomness appeared in the bond angle. We anticipate that these fundamental understanding can provide a guide for the discovery of TCO materials with optimized thermal properties.

Fabrication and Characterization of Nanostructured Tin doped Indium Oxide Coatings by the Instrument of Spray Pyrolysis

Nanostructured indium tin oxide (ITO) coating is one of the transparent conductive oxides (TCO) materials utilized as a transparent electrode. Due to its high demand in various applications like liquid crystal displays, touch screens, light emitting devices, and solar cells, ITO coatings have garnered significant research attention, owing to their excellent properties of high visible light transmittance and low resistance. Nanostructured coating of tin -doped Indium Oxide (ITO) was fabricated on glass slides utilizing the instrument of chemical spray pyrolysis (CSP), with varying levels of Sn-doping at 0, 3, 6, and 9 wt%. The effect of tin content on the many physical characteristics of the resulting coatings has been examined. The analysis of x-ray diffraction (XRD) displayed the characteristic orientations. The coatings have a polycrystalline cubic lattice structure along (400) as the preferred growth direction. Morphological measurements indicate that the samples possess a highly uniform surface and the grain size for the ITO samples is 100 nm displaying a nanostructure for all samples. The optical transmittance was measured over 75% for coating with tin content equal to 0wt%, while the transmittance of the Sn-doped films can range from 78% to 84% at 700 nm and the values of the direct bandgap were measured as 3.6, 3.65, 3.675, and 3.7eV for Sn doping 0, 3, 6, and 9 wt% respectively. In the visible area, the nanostructured ITO coatings exhibit elevated values of transmittance which makes them suitable for various optoelectronic applications such as window materials in solar cells. The results indicate a desirable reduction in the electrical resistivity with rising the number of carriers per unit volume and mobility with increasing tin content in the samples. The minimum electrical resistivity and maximum carrier concentration were achieved for ITO coating with tin content equal to 9wt%. The incorporation of Sn dopant significantly changes the overall electrical properties of indium oxide films, this is favorable for transparent conducting oxide.

Advancements in Transparent Conductive Oxides for Photoelectrochemical Applications.

Photoelectrochemical cells (PECs) are an important technology for converting solar energy, which has experienced rapid development in recent decades. Transparent conductive oxides (TCOs) are also gaining increasing attention due to their crucial role in PEC reactions. This review comprehensively delves into the significance of TCO materials in PEC devices. Starting from an in-depth analysis of various TCO materials, this review discusses the properties, fabrication techniques, and challenges associated with these TCO materials. Next, we highlight several cost-effective, simple, and environmentally friendly methods, such as element doping, plasma treatment, hot isostatic pressing, and carbon nanotube modification, to enhance the transparency and conductivity of TCO materials. Despite significant progress in the development of TCO materials for PEC applications, we at last point out that the future research should focus on enhancing transparency and conductivity, formulating advanced theories to understand structure-property relationships, and integrating multiple modification strategies to further improve the performance of TCO materials in PEC devices.

Design and fabrication of indium tin oxide for high performance electro-optic modulators at the communication wavelength

In recent years, transparent conductive oxides(TCO) based electro-optic modulators has garnered significant attention due to its epsilon-near-zero(ENZ) effect to enhance the local optical field and produce a large refractive index change in the vicinity of ENZ wavelength, thereby enabling substantial optical field modulation at micrometer size. The modulators manipulate the light field by altering the carrier concentration in TCO through an electric field. Therefore, the modulator's performance is closely related to the TCO's material behavior. In this paper, the effect of carrier concentration and mobility of indium tin oxide(ITO) on the modulation efficiency, depth and bandwidth was analyzed and it is found that ITO with the carrier concentration near 1 × 1020 cm−3 and mobility as high as 80 cm2/Vs is beneficial to the electro-optic modulators with large modulation depth and bandwidth. Specifically, our research shows that the carrier concentration and mobility of ITO films can be tunned over a wide range from 2.2 × 1019cm−3 to 7.7 × 1020cm−3 and 7.2 cm2/Vs to 82.3 cm2/Vs respectively, by changing doping concentration, deposition conditions and annealing parameters. As a result, ITO film integrated on a 3.5-μm-long silicon waveguide with an MOS structure can achieves a high modulation bandwidth of over 40 GHz at the optical communication wavelength.

Enhanced photocatalytic activity of graphene oxide incorporated ZnO nanorods doped with post-transition metals

Photocatalytic activity of graphene oxide incorporated pure and selected post-transition metal doped zinc oxide nanorods were investigated for the degradation of methylene blue dye. Thin film seed layers were deposited on microscopic glass slides using an automated spray pyrolysis technique at a substrate temperature of 425 °C. Aluminium, gallium, and indium were the metals used for doping. Graphene oxide content in the precursor solution was fixed at 0.00375 g/L. Nanorods of the aforesaid transparent conducting oxide materials were grown by aqueous chemical growth technique, vertically over the respective as-deposited seed layers. Structural and optical properties of the nanorods were studied. Growth of the vertical nanorods was confirmed by scanning electron microscopy. All the nanorod samples were utilized as catalysts for repeated cycles of photocatalysis and the graphene oxide incorporated indium doped zinc oxide nanorod was found to be an efficient and stable photocatalyst by degrading 96.1 % of methylene blue dye in 180 min under simulated solar irradiation.

Superior Conductivity of Transparent ZnO/MoS2 Composite Films for Optoelectronic and Solar Cell Applications.

The use of transparent conductive oxides in optoelectronics created a revolution where new-generation materials with high transmittance, low sheet resistance values, durability, and portability can be achieved without decreasing efficiency or increasing costs. Transparent ZnO/MoS2 sandwich-structured conductive composite films were produced in this study via the sol-gel method, which is considered the most efficient method due to its simple process and low cost. The crystal structure properties of ZnO/MoS2 were characterized via X-ray diffraction (XRD) patterns. The crystal sizes of ZnO films doped with different amounts of MoS2 were determined. A UV-visible absorption spectrometer was used to perform the spectroscopic analysis of the film. The area under the absorption curve and the full width of the half-maxima of absorbance data were calculated. Using these values, the optimum amount of MoS2 was determined for the best additive distribution. In addition, in order to determine the best transparent conductive material, resistance values measured via the four-point probe method were compared for different MoS2 additive amounts. The optical and electrical characterizations of transparent ZnO/MoS2 conductive oxide films were investigated. According to the parameters obtained via UV-vis spectroscopy, XRD, and four-point probe measurements, the most effective dispersion that exhibits a low width ratio and high resonance ratio was found for ZnO/MoS2 with a doping amount of 4 mg, the crystallite size of the films was found to be within the range of 21.5 and 24.6 nm, and these observations demonstrated a figure-of-merit value of more than 4.8 × 10-2 with respect to these sandwich-structured films. Compared to the values of previous studies on various transparent ZnO-doped conductive oxide materials, it is possible to claim that these new films have a structure that is very similar to the transparent conductivity characteristics of other films, and they may even be superior relative to some MoS2 amounts.

Study of the electronic properties of pure nanostructured hexagonal Zinc Oxide by DFT method

(ZnO) Zinc oxide is considered a semiconducting material from the family of transparent conductive oxide materials. Our study aims to study the electronic properties of pure Nano-sized hexagonal zinc oxide using the DFT method using the (GGA-PBE) approximation and the (HSE03) approximation, as we demonstrated through our study on the unit cell In the large cell (3×3×3) and the small cell (1×1×1), zinc oxide has a direct energy gap in the (GGA-PBE) approximation, and its value is (e V) 1.74) and in the (HSE03) approximation, the value of the energy gap is (e V2.79). The difference in the two approximations is very clear, and it is evidence that when using the (GGA-PBE) approximation for the DFT method, it reduces the value of the energy gap for zinc oxide, and when using the (HSE03) approximation, the energy gap increases because it is more mathematically accurate, even though it takes more time to calculate.

First-principles study on transition-metal doping and band-structure modulation in ZnO

Transparent conducting oxides (TCOs) have both the electrical conductivity of a metal and the optical transparency of an insulator. Due to this unique feature, TCO is utilized in various applications such as flat panel displays, solar cells, light emitting diodes, and smart windows. At present, Sn-doped In<sub>2</sub>O<sub>3</sub> (ITO) is the most widely used in the TCO market because of the superior materials properties. However, due to the demand for higher conductivity, instability of indium supply and high price, research to find new TCO materials has been continuously conducted. In this study, to develop a new TCO based on ZnO, we investigate the thermal stability of the transition metal dopants Sc and V and their effect on the band structure of ZnO using first-principles calculations. Our results show that Sc and V are efficient donors that can generate one free electron by substituting Zn when doped into ZnO. Furthermore, by analyzing the band structure of the doped system and calculating the electron effective mass, we show that Sc and V doping can be an important strategy to develop ZnO-based high-performance TCOs.

Transparent Conducting Oxide Nanocrystals: Synthesis, Challenges, and Future Prospects for Optoelectronic Devices

Flexible transparent electrodes are prerequisites of next‐generation electronic devices. Most of the synthesis process of conventional transparent conducting oxides (TCOs) require high vacuum and high temperature, which hinder its application in flexible devices. Colloidal TCO nanocrystals (NCs) can be potential candidates in this regard. But till date, the electrical performances are not promising for commercial applications. Therefore, a detailed understanding of synthesis, electrical transport, and challenges is required for further development of colloidal NC‐based transparent electrode. Herein, notable works with emphasis on synthesis, postsynthesis modification, along with film deposition techniques are summarized. The comparative studies of electrical performance of promising TCO materials with its thin‐film counterpart are presented to draw future prospects of TCO NCs as commercial transparent electrodes.

All-optical passive photonic diodes based on perovskite and transparent conducting oxide material

Low dimensional perovskite emerging as a highly promising class of functional materials for semiconductor optoelectronic applications have drawn great attention. Here, we report the nonlinear absorption of low-dimensional perovskite PEA2PbI4 and transparent conducting oxide material Aluminum-doped zinc oxide (AZO) with operating spectral window in telecommunications. Then we fabricate all-optical diodes with nonreciprocity factor of 10.1 dB based on the reverse saturable absorber (PEA2PbI4) and the saturable absorber (AZO). The results show the potential applications of perovskite-based materials in all-optical diode, and may pave way for the development of high-performance photonic devices.

Optically Transparent MIMO Antenna with Polarisation Diversity for Vehicular Communications

ABSTRACT A unique multiple-input-multiple-output (MIMO) adaptive intelligent antenna for vehicular communications is addressed in this article. It has a high degree of transparency that can be integrated with the windscreen for intelligent vehicular communications. The proposed diversity antenna has four monopole radiators oriented in orthogonal directions to obtain polarisation diversity. The optically transparent nature is realised using a soda-lime substratum of size 50 × 50 mm2 coated with Transparent Conductive Oxides (TCO). The Aluminium Zinc Oxide (AZO) is sputtered on top of a Fluorine Tin Oxide (FTO) to enhance the material’s conductivity with dual-conductive layer. The fabricated MIMO antenna has a bandwidth of 10 GHz and functions in the entire UWB range (2 to 12 GHz). By incorporating concentric circles into the ground, high confinement between nearly located antenna elements is achieved. The antenna has a peak gain of 2.9 dBi as measured. The Envelope Correlation Coefficient (ECC) of the antenna in the entire Ultra-wideband (UWB) region attributed to the TCO material shows a very low correlation among the antenna elements. Because of diversity gain of the proposed vehicular antenna is ˃ 9.8 dB, it can also operate with low transmission power. The findings indicate that the antenna is pertinent for current intelligent vehicles that require multiple communications without aesthetic hindrance.

Fabrication of High Transmittance and High Mobility Transparent Conductive Oxide Films: Hydrogen-doped Indium Oxide

Designing and fabricating high-performance transparent conductive oxides (TCOs) is an attractive area for optoelectronic devices that require both high transparency and electrical conductivity. In this study, we introduce a hydrogen doping of indium oxide (IHO) as a TCO material with enhanced transparency while maintaining high conductivity by optimizing the carrier mobility, carrier concentration, and thickness. The typical IHO with a thickness of 200 nm exhibits a relatively lower carrier concentration (~2.10*1020 cm−3), compared to the traditional TCO like indium tin oxide and results in a higher NIR transmission of over 55% at 2500 nm, while the high carrier mobility of 87 cm2 V−1 s−1 endows it a lower sheet resistance of 15 Ω/sq. Our research provides valuable insights into the TCO and can be a general strategy to enhance light utilization for energy-efficient optoelectronic devices. Our work provides valuable insights into how the properties of TCOs can be tuned by controlling their microstructure and doping. The results show that hydrogen doping is an effective strategy to achieve the desired optical and electrical characteristics for efficient utilization of light in optoelectronics.

Comparative Performance Evaluation of Transparent Conducting Oxides With Different Mobilities for All-Optical Switching in Silicon

All-optical switching is an appealing approach for signal processing, optical communications or sensing systems. In this work, we compare the performance of doped cadmium oxide, aluminum doped zinc oxide, and indium tin oxide as transparent conducting oxide (TCO) materials with different mobilities in thin-film configuration integrated into a hybrid silicon photonic waveguide. Our results reveal the best operational parameters and trade-offs for enabling high-performance and energy-efficient switching by using TCOs with moderate mobility but more environmental-friendly. Extinction ratios of 10 dB∙μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and insertion losses of 2 dB∙μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> are achieved by an AZO/Si amplitude switch with an energy consumption of only 90 fJ. These results reveal that cadmium-free TCO materials can also be leveraged to build high-performance all-optical switches in silicon.