Transparent Conducting Oxide Materials Research Articles

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.

Temperature Dependence on Structural Properties of Liquid Phase Synthesized ZnO

Transparent conducting oxide material, ZnO nanoparticles has been synthesized using inexpensive and eco-friendly synthesis procedures with less or environmental pollutants and no liquid waste products. The effect of the temperatures on the structural properties for the synthesized ZnO nanocrystals has been investigated. In this study, we report an easy, low-cost, re-producible method for synthesizing ZnO nanoparticles by means of the liquid phase method. The ZnO nanocrystals were synthesized using the wet chemical route and the effect of temperature variation on the structural properties of investigated synthesized using powder x-ray diffractogram (XRD). The temperatures for the synthesis were varied from 120 °C to 200 °C in steps of 20 °C. The results show that, during the first stage of the synthesis of ZnO (at 120 °C), the XRD diffraction pattern confirms the cubic structure of zinc peroxide and the XRD pattern of the samples obtained at temperatures of 140 °C, 160 °C, 180 °C and 200 °C were confirmed to be hexagonal (wurtzite) crystal structure of ZnO. The XRD diffraction patterns of the 140 °C and 160 °C samples show some impurity phases which were associated with the zinc acetate by-product which is a colloid complex of water and methyl succinate and were removed by evaporation as temperatures were increased to 180 °C and 200 °C respectively. As temperature increases, the peak of the diffractograms of the sample becomes sharper and narrow indicating a decrease in width. A shift in peak positions to higher angles was observed and the positional parameter, bond angle, β, average crystallite size, APF, number of unit cells and density generally increase with temperature. However, the lattice parameters ‘a’ and ‘c’, bond lengths b and b1, bond angle, α, dislocation density, strain and unit cell volume were found to generally decrease with temperature.

A Brief Review of Transparent Conducting Oxides (TCO): The Influence of Different Deposition Techniques on the Efficiency of Solar Cells

Global-warming-induced climate changes and socioeconomic issues increasingly stimulate reviews of renewable energy. Among energy-generation devices, solar cells are often considered as renewable sources of energy. Lately, transparent conducting oxides (TCOs) are playing a significant role as back/front contact electrodes in silicon heterojunction solar cells (SHJ SCs). In particular, the optimized Sn-doped In2O3 (ITO) has served as a capable TCO material to improve the efficiency of SHJ SCs, due to excellent physicochemical properties such as high transmittance, electrical conductivity, mobility, bandgap, and a low refractive index. The doped-ITO thin films had promising characteristics and helped in promoting the efficiency of SHJ SCs. Further, SHJ technology, together with an interdigitated back contact structure, achieved an outstanding efficiency of 26.7%. The present article discusses the deposition of TCO films by various techniques, parameters affecting TCO properties, characteristics of doped and undoped TCO materials, and their influence on SHJ SC efficiency, based on a review of ongoing research and development activities.

Influence of oxygen on the optical, electrical, and heating properties of gallium-doped zinc oxide (GZO) films

Thin-film transparent heaters (TFTHs) are gaining popularity in optoelectronics and a variety of domestic applications, including smart windows, car defrosters, and other devices. The deposition and characterization of TFTHs made of gallium-doped zinc oxide (GZO) are presented in this work. GZO thin films were deposited via pulsed laser deposition on glass substrates with varying oxygen partial pressures from 0 to 10 mTorr during deposition. The samples demonstrated very low sheet resistance values between 5 and 17 Ω/sq from 0 to 10 mTorr, respectively. UV/vis transmission spectra revealed that TFTHs have a high optical transparency above 80%. GZO-based TFTHs demonstrated a consistent and repeatable joule heating effect, with temperatures reaching 76 °C with a low input voltage of 10 V. This research could guide the future use of GZO as a transparent conducting oxide material for many potential cost-effective applications from low-powered electronics to lightweight and wearable devices.

Hydrolysis and condensation of monobutyltin chloride: reaction process analysis with DFT.

As the initial process of preparing transparent conductive oxide materials from monobutyltin chloride (MBTC) to tin oxide, the hydrolysis and condensation of MBTC to form a dimer Sn2 play a critical role. However, the specific mechanism of this process is still unclear. Here we develop a step-by-step searching method based on density functional theory calculation and empirical chemical criteria to determine possible reaction pathways and reveal the most likely reaction mechanism. The wave function analyses of various intermediate species provide more insights into the changes of atomic charge population, chemical bond strength, and coordination situation of central tin in the reaction process. Further investigation on the ring-containing Sn2 reveals the existence of unique three-center four-electron (3c-4e) interactions to stabilize the four-membered Sn2O2 ring structure, which serves as the true driving force for dimerization reaction. These results provide a more detailed understanding of the hydrolysis and condensation process of MBTC and would be helpful for the future optimization of the preparation process of tin oxide films.

Electrically switchable Casimir forces using transparent conductive oxides

Casimir forces between charge-neutral bodies originate from quantum vacuum fluctuations of electromagnetic fields, which exhibit a critical dependence on material's electromagnetic properties. Over the years, in situ modulation of a material's optical properties has been enabled through various means and has been widely exploited in a plethora of applications such as electro-optical modulation, transient color generation, bio- or chemical sensing, etc. Yet Casimir force modulation has been hindered by difficulty in achieving high modulation signals due to the broadband nature of the Casimir interaction. Here we propose and investigate two configurations that allow for in situ modulation of Casimir forces through electrical gating of a metal-insulator-semiconductor junction comprised of transparent conductive oxide (TCO) materials. By switching the gate voltage on and off, a force modulation of &gt;400 pN is predicted due to substantive charge carrier accumulation in the TCO layer, which can be easily measured using state-of-the-art force measurement techniques in an atomic force microscope. We further examine the influence of the oxide layer thickness on the force modulation, suggesting the importance of the fine control of the oxide layer deposition. Our work provides a promising pathway for modulating the Casimir effect in situ with experimentally measurable force contrast.

Effect of Laser Scribing on Coating, Drying, and Crystallization of Absorber Layer of Perovskite Solar Cells

Large‐area perovskite solar modules fabrication has been demonstrated with a rapid process of large‐area slot‐die coating, drying, and crystallization using near‐infrared radiation in ambient air, in which the laser‐scribing process is applied to fabricate the modules. However, defective coating of perovskite layer near laser‐scribed P1 line which isolates the front electrode of transparent conductive oxide (TCO) results very low module efficiencies. Therefore, systematic study is conducted to investigate the root cause, mechanism and solution of the defective coating and crystallization of the perovskite layer. Scanning electron microscope, energy‐dispersive X‐ray spectroscopy, and atomic force microscopy are used to characterize the TCO film before and after P1 scribing. It is found that P1 laser‐scribing process changes surface morphology of TCO at the area near P1 line, which decreases the surface wettability and results discontinuous coating of precursor solution near P1 lines. The absence of TCO material in the P1 trench induces nonuniform heating during NIR annealing step, which is verified by thermal analysis via numerical simulation. After tuning laser process recipes, a large module with an active area of 46 cm2 is fabricated with a power conversion efficiency of 7.2% and geometry fill factor of 93.8%.