Tin-doped Indium Oxide Films Research Articles

One-Stone-for-Two-Birds Method to Improve the SnO2 Layers for High Power-per-Weight Flexible Perovskite Solar Cell Mini-modules.

Maintaining the power conversion efficiency (PCE) of flexible perovskite solar cells (fPSCs) while decreasing their weight is essential to utilize their lightweight and flexibility as much as possible for commercialization. Strengthening the interfaces between functional layers, such as flexible substrates, charge transport layers, and perovskite active layers, is critical to addressing the issue. Herein, we propose a feasible and one-stone-for-two-birds method to improve the electron transport layer (ETL), SnO2, and the interface between the ETL and perovskite layer simultaneously. In detail, poly(acrylate ammonium) (PAAm), a low-cost polymer with a long chain structure, is added into the SnO2 aqueous solution to reduce the aggregation of SnO2 nanoparticles, resulting in the deposition of a conformal and high-quality ETL film on the tin-doped indium oxide film surface. Simultaneously, PAAm addition can effectively regulate the crystallization of the perovskite films, strengthening the interface between the SnO2 film and the buried surface of the perovskite layer. The outstanding PCEs of 22.41% on small-scale fPSCs and 18.54% on fPSC mini-modules are among the state-of-the-art n-i-p type fPSCs. Moreover, the fPSC mini-module on the 20 μm-thick flexible substrate shows a comparable PCE with that of the fPSC mini-module on the 125 μm-thick flexible substrate, exhibiting a high power-to-weight of 5.097 W/g. This work provides an easy but essential direction for further applications of fPSCs in diverse scenarios.

Bi2O3 doped indium tin oxide thin films fabricated via liquid metal printing

Indium tin oxide (ITO) is a classical transparent conducting oxide (TCO), which is widely used in semiconductor industry. Reducing the cost of preparing ITO films and further improving its optoelectronic properties are urgent technological challenges to be solved. Here, we proposed to tackle this issue through doping elements in ITO films via liquid metals printing process. Conceptual experiments demonstrate the synthesis of Bi2O3 doped ITO at the centimeter scale using low-temperature fabrication techniques, which display the advantages of high uniformity, strong visible light transmission and low resistivity. The band gap decreases from 3.88 eV to 3.07 eV with increasing doping of Bi2O3 and demonstrates n-type semiconductor nature. The Schottky diodes based on doped ITO films show typical Ohmic contact. The best output current of doped ITO Schottky diodes can reach 1261.7 μA at 10 V, which is about 41 times the output current of the undoped ITO Schottky diodes. Additionally, the nanofilm resistance decreased linearly with increasing Bi mass fraction in ITO film. Moreover, Schottky diodes have good stability in the atmosphere within half a year and multilayer printing can enhance output current. The process as established here offers significant opportunities for future synthesis and fabrication processes in the electronics industries.

Reorganization Energies for Interfacial Electron Transfer across Phenylene Ethynylene Rigid-Rod Bridges.

A family of three ruthenium bipyridyl rigid-rod compounds of the general form [Ru(bpy)2(LL)](PF6)2 were anchored to mesoporous thin films of tin-doped indium oxide (ITO) nanocrystals. Here, LL is a 4-substituted 2,2-bipyridine (bpy) ligand with varying numbers of conjugated phenylenethynylene bridge units between the bipyridine ring and anchoring group consisting of a bis-carboxylated isophthalic group. The visible absorption spectra and the formal potentials, Eo(RuIII/II), of the surface anchored rigid-rods were insensitive to the presence of the phenylene ethynylene bridge units in 0.1 M tetrabutyl ammonium perchlorate acetonitrile solutions (TBAClO4/CH3CN). The conductive nature of the ITO enabled potentiostatic control of the Fermi level and hence a means to tune the Gibbs free energy change, -ΔG°, for electron transfer from the ITO to the rigid-rods. Pseudo-rate constants for this electron transfer reaction increased as the number of bridge units decreased at a fixed -ΔG°. With the assumption that the reorganization energy, λ, and the electronic coupling matrix element, Hab, were independent of the applied potential, rate constants measured as a function of -ΔG° and analyzed through Marcus-Gerischer theory provided estimates of Hab and λ. In rough accordance with the dielectric continuum theory, λ was found to increase from 0.61 to 0.80 eV as the number of bridge units was increased. In contrast, Hab decreased markedly with distance from 0.54 to 0.11 cm-1, consistent with non-adiabatic electron transfer. Comparative analysis with previously published studies of bridges with an sp3-hybridized carbon indicated that the phenylene ethynylene bridge does not enhance electronic coupling between the oxide and the rigid-rod acceptor. The implications of these findings for practical applications in solar energy conversion are specifically discussed.

Optical properties of highly-crystalline tin-doped indium oxide films in their near-zero permittivity spectral region

Transparent conducting oxides (TCOs) have recently attracted much attention in the fields of optics and photonics because of their outstanding linear and nonlinear optical response in the near-zero permittivity spectral region. The optical response of these materials can be further enhanced by optimizing the material properties through fabrication. In particular, two important TCO parameters affecting the strength of the optical interactions are the optical mobility and effective mass of free electrons. In this work, we fabricate epitaxial, highly-textured, and polycrystalline tin-doped indium oxide (ITO) films to experimentally study the effect of the crystal quality on the optical mobility and effective electron mass, and on the optical properties of the material in the near-zero permittivity spectral region. Compared to polycrystalline ITO, we report an increase in the optical mobility from 38 to 67 cm2/Vs and a reduction in the effective mass from 0.3 m0 to 0.24 m0 in oxygen-deficient epitaxially grown ITO films. The improved material parameters reduces the imaginary part of the permittivity (from 0.56 to 0.42) and results in a steeper material dispersion for the high-crystal-quality ITO films. Based on these results, an analysis of the figure of merit for nonlinear refraction reveals that epi- and tex-ITO films can achieve a stronger nonlinear response than poly-ITO samples. Our results show that controlling the free-electron optical mobility and effective mass through crystal quality along with tuning the free-electron density allows for tailoring simultaneously the near-zero-permittivity wavelength and the optical losses at that wavelength, which is of utmost importance for the ENZ photonics applications.

Optical Property Change of Silver Nanowire Thin Films in Laser Patterning Process

Silver nanowire thin films are attractive materials for flexible electrodes as an alternative for conventional tin-doped indium oxide films. An appropriate patterning process is required to apply nanowire-based transparent electrodes into the optoelectronic devices. In this paper, we report the optical property change in silver nanowire transparent electrodes during laser ablation process. We discovered that, when silver nanowires were patterned by nanosecond pulsed lasers at infrared wavelength, their optical properties were changed. The change of optical properties was caused by nanoresidues remaining on the surface. It was analyzed that the color and transparency of thin films were changed because the residual nanoparticles absorbed the visible light wavelengths where silver nanoparticles possess their peak values in the absorption spectra. The nanoparticles were derived from insufficient vaporization of silver nanowires during infrared laser ablation. In the case of using an excimer laser for patterning, the nanoparticles were not left more on the surface due to complete removal of silver nanowires, since silver has higher absorption coefficient at the wavelength of excimer laser. As a result, high-quality patterning of silver nanowire thin films could be obtained without any deterioration of optical properties in transparent electrodes.

Ultrathin, highly flexible and optically transparent terahertz polarizer based on transparent conducting oxide

Multifunctional terahertz devices hold great promise for terahertz (THz) optical systems. Here, we present an ultrathin, highly flexible and optically transparent terahertz polarizer based on tin-doped indium oxide (ITO) and flexible conformal films of polyethylene terephthalate. The flexible optical transparent polarizer (FOTP) was theoretically investigated and experimentally characterized by UV–vis spectrophotometry and THz time-domain system. In the FOTP, THz conductivity of ITO films is mainly dominated by DC conductivity. The FOTP reveals a high optical transmittance of more than 60% in the visible region, a high extinction ratio of about 20 dB in the 0.1 THz–2.5 THz and a low insertion loss below 2 dB in the 0.1 THz–1.4 THz. The proposed FOTP can significantly improve the overall performance of THz optical systems and be easily fabricated by commercial display techniques. Our concept opens up a new window for highly flexible and optically transparent THz devices.

Annealing effect on indium tin oxide thin films by DC magnetron sputtering for alkali vapor cell heating

This paper reports the annealing effect on the DC sputter transparent conducting tin-doped indium oxide (ITO) films for the alkali vapor cell heater of the chip-scale atomic sensors. ITO films with a thickness of 140 nm were deposited on BF33 glass substrates at [Formula: see text], followed by an annealing process in N2 atmosphere for 2 h at different temperatures between [Formula: see text] and [Formula: see text]. The effect of annealing on the crystal structure, surface morphology, optical, and electrical properties of ITO films was characterized. The predominant orientation of crystal face of the as-deposited and annealed ITO thin films was (222) instead of (400). After annealing at [Formula: see text] the ITO film exhibits the highest transmittance ([Formula: see text][Formula: see text]90%) to the lights at the wavelength of 780 nm, 795 nm and 894 nm regarding the probe light in a chip scale atomic device. Besides, the lowest sheet resistance and resistivity were obtained as 27.8 [Formula: see text] and [Formula: see text] separately. The refractive index and extinction coefficients results verified the crystal orientation and the transmittance results. This thin ITO film was expected to be the best candidate for the transparent heater in the chip scale atomic devices.

Study of Sputtered ITO Films on Flexible Invar Metal Foils for Curved Perovskite Solar Cells

We have studied characteristics of tin-doped indium oxide (ITO) films sputtered on flexible invar metal foil covered with an insulating SiO2 layer at room temperature to use as transparent electrodes coated substrates for curved perovskite solar cells. Sheet resistance, optical transmittance, surface morphology, and microstructure of the ITO films on SiO2/invar substrate are investigated as a function of the thickness from 50 to 200 nm. The optimized ITO film exhibits a low sheet resistance of 50.21 Ohm/square and high optical transmittance of up to 94.31% even though it is prepared at room temperature. In particular, high reflectance of invar metal substrate could enhance the power conversion efficiency of curved perovskite solar cell fabricated on the ITO/SiO2/invar substrate. In addition, critical bending radius of the 150 nm-thick ITO film is determined by lab-designed outer and inner bending tests to show feasibility as flexible electrode. Furthermore, dynamic fatigue test is carried out to show flexibility of the ITO film on invar metal substrate. This suggests that the ITO/SiO2/invar substrate can be applied as flexible electrodes and substrates for curved perovskite solar cells.

Optimization of Nano-structured Tin Doped Indium Oxide Films Grown at Substrate Temperature close to the Melting Point of Tin

Abstract For efficient utilization of In2O3:Sn (ITO) films in device structures, a low-temperature growth is always preferred. However, optical transparency and electrical conductivity of the transparent-conducting-oxide (TCO) films always hold a trade-off relation in-between. For accommodating all such stringent requirements, ITO films in the present investigation has been deposited on glass substrates using 13.56 MHz RF magnetron sputtering and optimized at temperature close to the melting point of Sn as a dopant to the In2O3 network, in order to utilize its best favorable contribution to the growth of properly doped films having balanced combination of relevant optical, electrical and nano-structural properties. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i-2017).

Fluorine- and tin-doped indium oxide films grown by ultrasonic spray pyrolysis: Characterization and application in bifacial silicon concentrator solar cells

Multi-wire metallization and interconnection for silicon solar cells is considered as a revolutionary technology for the next generation of photovoltaic modules, since it drastically reduces their cost while boosting efficiency. In this paper, we report results obtained using an innovative approach for the fabrication of bifacial low-concentrator Ag-free Cz-Si (Czochralski silicon) solar cells based on an indium fluorine oxide (IFO)/(n+pp+)Cz-Si/indium tin oxide (ITO) structure. Transparent conducting oxide (TCO) layers, IFO and ITO, acting as antireflection electrodes, were grown by ultrasonic spray pyrolysis (USP). A copper wire contact pattern was attached by low-temperature lamination simultaneously to the front and rear TCO layers as well as to the interconnecting ribbons located outside the structure (laminated grid cell (LGCell) design). In this paper, to extend the operating range of sunlight concentration ratios of LGCells, the sheet resistance of the IFO and ITO layers has been reduced to 14 and 13Ω/sq, respectively, by increasing their thickness by about three times, from ∼85 to ∼240 nm. As a result, the operating range of the LGCells has been extended to 1–7suns. In the operating range, their front-illumination efficiency varies from 18.3 to 18.9% (back-illumination efficiency from 15.1 to 15.6%). We also report for the first time the results of systematic analysis of USP IFO properties and compare them with the USP ITO properties. The effect of the IFO thickness on grain size, electrical resistivity, charge carrier concentration and mobility, refractive index, transmission and absorption spectra, as well as optical band gap has been analyzed systematically by scanning electron microscopy, transmission and reflection spectra, optical ellipsometry and Hall measurements.

Thermally ruggedized ITO transparent electrode films for high power optoelectronics.

We present two strategies to minimize laser damage in transparent conductive films. The first consists of improving heat dissipation by selection of substrates with high thermal diffusivity or by addition of capping layer heatsinks. The second is reduction of bulk energy absorption by lowering free carrier density and increasing mobility, while maintaining film conductance with thicker films. Multi-pulse laser damage tests were performed on tin-doped indium oxide (ITO) films configured to improve optical lifetime damage performance. Conditions where improvements were not observed are also described. When bulk heating is not the dominant damage process, discrete defect-induced damage limits damage behavior.

A concise way to estimate the average density of interface states in an ITO–SiOx/n-Si heterojunction solar cell

On the basis of a photon-assisted high frequency capacitance–voltage (C–V) method (1MHz C–V), an effective approach is developed to evaluate the average interface state density (Dit) of an ITO–SiOx/n-Si heterojunction structure. Tin-doped indium oxide (ITO) films with different thicknesses were directly deposited on (100) n-type crystalline silicon by magnetron sputtering to fabricate semiconductor–insulator–semiconductor (SIS) hetero-interface regions where an ultra-thin SiOx passivation layer was naturally created. The morphology of the SiOx layer was confirmed by X-ray photoelectron spectroscopy depth profiling and transmission electron microscope analysis. The thinness of this SiOx layer was the main reason for the SIS interface state density being more difficult to detect than that of a typical metal–oxide–semiconductor structure. A light was used for photon injection while measuring the C–V of the device, thus enabling the photon-assisted C–V measurement of the Dit. By quantifying decreases of the light-induced-voltage as a variation of the capacitance caused by parasitic charge at interface states the passivation quality within the interface of ITO–SiOx/n-Si could be reasonably evaluated. The average interface state density of these SIS devices was measured as 1.2–1.7×1011eV−1cm−2 and declined as the passivation layer was made thicker. The lifetime of the minority carriers, dark leakage current, and the other photovoltaic parameters of the devices were also used to determine the passivation.

Effects of processing parameters on crystalline structure and optoelectronic behavior of DC sputtered ITO thin film

DC magnetron sputtering technique has been used to deposit highly transparent and conducting films of tin-doped indium oxide (ITO) onto externally unheated glass substrate, with and without annealing. The ITO thin films were obtained by varying the working pressure and the DC power as critical process parameters. The effects of variation of the deposition parameters on the deposition rate, microstructural, electrical, and optical properties have been investigated in this paper to study electro-optical characteristics of ITO films. The microstructural, electrical and optical properties of the sputtered ITO films were systematically characterized by X-ray diffraction, atomic force microscopy, four probe electrical conductivity and optical spectroscopy. A minimum sheet resistance \(16 \,\varOmega\)/square and transmittance 85 % with a Haacke’s figure of merit \(12 \times {10^{ - 3}} \,{\varOmega ^{ - 1}}\), thickness of 230 nm and optical band gap 4.09 eV are obtained for the thin films grown on externally unheated substrate at 100 W DC power and 32 mTorr working pressure.

Understanding the role of mobility of ITO films for silicon heterojunction solar cell applications

Transparent conducting oxides (TCO) are crucial in amorphous/crystalline silicon heterojunction solar cells performance as they have to be highly conductive to ensure the transport of photogenerated charges while remaining highly transparent to the sun spectrum. The key parameter to improve the transparency/conductivity compromise of TCO is mobility, since it allows increasing conductivity without losing transparency in the infrared region. A deep understanding of the factors influencing the mobility is then fundamental, and this is the objective of this paper. For this study, thin films of tin-doped indium oxide (ITO) were prepared by magnetron sputtering with different oxygen content. They were deeply characterized by standard and Low Temperature Hall Effect measurement, scanning and transmission electron microscopy and X-ray diffraction. The impact of oxygen on the microstructure was studied and the electrical properties were deeply investigated. In particular, the different mechanisms impacting the mobility were quantified as a function of oxygen content during ITO deposition.

Tin-doped indium oxide films for highly flexible transparent conducting electrodes

With the recent growing interest in flexible electronics, many studies are being conducted on flexible transparent conducting electrodes (TCE) such as Ag nanowires, Ag nanomeshes, carbon nanotubes, and graphenes. However, it will take time for such technologies to replace Sn-doped In2O3 (ITO), which is now widely used, due to challenges with reliability, mass-production, cost, and industry infrastructure. In this study, ITO films with different thicknesses were deposited on a flexible polymer substrate to investigate their optical and electrical properties and flexibility as a function of film thickness. Regardless of thickness, the ITO films' transmittance was about 80% at ~550nm wavelength. The sheet resistances of all films were below 100Ω/sq although resistance increased with decreasing film thickness. As a result of bending tests, it was found that thinner films had a higher threshold against bending strain. The sheet resistances did not significantly change above a bending radius of ~5mm. In particular, the 50nm-thick ITO film endured to a bending radius of ~3mm, showing that it is a viable transparent electrode for flexible optoelectronics.

Optical properties of undoped and tin-doped nanostructured In2O3thin films deposited by spray pyrolysis

Tin-doped indium oxide (In 2 O 3 :Sn) thin films in different concentrations (Sn = 0, 3, 5, 8 at.%) were deposited by reactive chemical pulverisation spray pyrolysis on heated glass substrates at 500 °C. The effect of the tin dopant on the nonlinear optical properties was investigated using X-ray diffraction, transmission, electrical resistivity and third harmonic generation (THG). All films were polycrystalline, and crystallised in a cubic structure with a preferential orientation along the (400) direction. The Sn (5 at.%) doped In 2 O 3 thin films exhibited a lower resistivity of 3 × 10 -4 Ω cm, and higher transmission in the visible region of about 94%. Optical parameters, such as the extinction coefficient ( k ), refractive index ( n ) and energy band gap ( E g ), were also studied to show the composition-dependence of tin-doped indium oxide films. The nonlinear properties of the In 2 O 3 :Sn thin films have been found to be influenced by doping concentration, and the best value of χ (3) = 3 × 10 -11 (esu) was found for the 5 at.% doped sample.

Paramagnetic Meissner Effect in Electrochemically Doped Indium-Tin Oxide Films

Transparent conductive indium-tin oxide (ITO) thin films, electrochemically intercalated with alkali (Li+, Na+, K+, Rb+, Cs+), alkali earth (Mg+2, Ca+2), or complex NH\(_{4}^{+}\) ions, show tunable superconducting transitions with dome-shaped behavior of Tc versus electron density around the maximum at ∼ 5 K. On field cooling, the transition into the superconducting state is accompanied by a paramagnetic response, i.e., an increase of magnetization, rather than the usual diamagnetic Meissner response. We provide an extensive study of this so-called paramagnetic Meissner effect (PME), using DC SQUID, transport measurements and a variety of sample sizes and growth conditions. We show that the PME in electrochemically doped ITO films results from a higher Tc at the sample edges than at the center of disk-shaped samples, causing flux to be expelled towards the center of the disk, following the flux-compression theory of Koshelev and Larkin. Changing to the opposite spatial Tc profile largely removes the paramagnetic response. The paramagnetic magnetization is strongly influenced by sample geometry and flux pinning conditions. The reduction of pinning defects by thermal annealing removes the paramagnetic response. An alternation of the external magnetic field restores the usual Meissner diamagnetism.

Zero added oxygen for high quality sputtered ITO: A data science investigation of reduced Sn-content and added Zr

The authors demonstrate mobilities of >45 cm2/V s for sputtered tin-doped indium oxide (ITO) films at zero added oxygen. All films were deposited with 5 wt. % SnO2, instead of the more conventional 8–10 wt. %, and had varying ZrO2 content from 0 to 3 wt. %, with a subsequent reduction in In2O3 content. These films were deposited by radio-frequency magnetron sputtering from nominally stoichiometric targets with varying oxygen partial pressure in the sputter ambient. Anomalous behavior was discovered for films with no Zr-added, where a bimodality of high and low mobilities was discovered for nominally similar growth conditions. However, all films showed the lowest resistivity and highest mobilities when the oxygen partial pressure in the sputter ambient was zero. This result is contrasted with several other reports of ITO transport performance having a maximum for small but nonzero oxygen partial pressure. This result is attributed to the reduced concentration of SnO2. The addition of ZrO2 yielded the highest mobilities at >55 cm2/V s and the films showed a modest increase in optical transmission with increasing Zr-content.

Effect of tin-doped indium oxide film on electrodeposition of ZnO nanostructures

Surface studies are reported for the deposition of ZnO nanostructures by one-step electrodeposition method. The electrosynthesis was perfomed at the surface of tin doped indium oxide coated glass substrates in the absence of any buffer layer. The growth of ZnO nanostructures was investigated with the morphology of substrate and the deposition mode. Combined nucleation mode was observed for the ZnO independently of substrate. The results indicated the growth, morphology and density of the ZnO nanostructures are markedly influenced by both the substrate and the deposition conditions. It was observed the ZnO formation is defect site driven in case of galvanostatic deposition mode, while in case of potentiostatic deposition mode, it is dependent on the roughness of the substrate.

Electrical and optical properties of nanosized films of doped zinc and indium oxides deposited by RF magnetron sputtering at room temperature

We have compared the electrical and optical properties of nanosized films of tin-doped indium oxide (ITO) and aluminum-doped zinc oxide (AZO) deposited on silicon and glass substrates by low-power RF magnetron sputtering at room temperature. Dependences of the resistivity and optical transmission coefficient of deposited oxides on the RF radiation power are presented. The plots of resistivity versus RF sputtering power for both oxides are nonlinear, with a minimum in the region of 50 W. For AZO, this minimum has been observed for the first time. The minimum value of resistivity for AZO is about 2.9 × 10−3 Ω cm and that for ITO is about 5.4 × 10−4 Ω cm. Both oxides are characterized by high optical transmission coefficients, close to 90% in a wavelength range of 500–1000 nm.