Fluorine-doped Tin Oxide Thin Films Research Articles

Failure Mechanisms of Fluorine-Doped Tin Oxide Thin Films in Glass and Reliability Tests

Failure Mechanisms of Fluorine-Doped Tin Oxide Thin Films in Glass and Reliability Tests

Preparation and characterization of graphene-based fluorine doped tin dioxide thin films via spray pyrolysis technique

Abstract In this work, fluorine-doped tin oxide (FTO) and graphene/fluorine-doped (G-FTO) thin films were prepared using a low-cost spray pyrolysis method at a substrate temperature of 500 °C. For the FTOs, stannous chloride was dissolved in methanol and acetic acid to form the precursor solution. A 0.05 mole (M) of hydrofluoric acid was added to the precursor as an n-type impurity. The FTO thin film has an optical transmittance of 82% and electrical sheet resistance of 15 Ω/□. By meticulously integrating graphene into the optimal precursor solution of FTO, a significant improvement in the electrical conductivity of the prepared samples was achieved, leading to a reduction in the sheet resistance to 8 Ω/□ with a suitable optical transmittance of 79%. Structural, morphological, optical, and electrical properties of the prepared sample are investigated using X-ray diffraction, scanning electron microscope, UV spectroscopy, and four-point probe technique. The best performance of the FTO thin films is achieved utilizing 2.5 µmole/L of fluorine concentration at a substrate temperature of 500°C for a spraying exposer time of 20 min. The prepared sample has an electrical sheet resistance of 15 Ω/□, optical transmittance of 82%, and figure-of-merit of 91.2×10−4 Ω−1.The addition of 0.4 µmole/L of graphene to the optimum FTO samples enhances the performance by a remarkable reduction in the electrical the sheet resistance to 8 Ω/□ and an acceptable reduction in the optical transmittance of 79%. The overall value of the figure-of-merit increased to 118.3×10−4 Ω−1. The achieved results offer a high potential for adopting the prepared films for electronic and optoelectronic applications.

Fluorine-Doped Tin Oxide Thin Films with High Surface Conductance and Low Transparency for Boosting Performance in Dye-Sensitized Solar Cell Applications

Transparent conductive oxide films, like fluorine-doped tin oxide (FTO), are needed for electrochemical devices. FTO films are attractive due to their cost-effectiveness and high-temperature tolerance. Generally, solar cell fabrication requires high transmittance and low-conductivity FTOs. However, achieving both simultaneously poses a fundamental challenge. This study investigates the impact of FTO layer thickness, sheet resistance, transparency, and film morphology on optimizing the performance of dye-sensitized solar cells. To achieve this, a precursor solution containing SnCl4·5H2O and NH4F in isopropanol is sprayed onto a soda-lime glass substrate at 500 °C to form FTO films. The film thickness is varied by repeating the spray cycles. By increasing the number of spray cycles, the sheet resistance of the FTO film improves to ∼1.20 Ω □–1 with the expense of transmittance. The achieved very low sheet resistance of ∼1 Ω □–1 (∼3.54 × 10–4) Ω cm resistivity for the FTO film confirms the promise of this sequential spray pyrolysis technique in preparing highly conductive inert electrodes for various applications. Furthermore, DSCs with low transparency and sheet resistance showed higher-energy conversion efficiencies, challenging the current prerequisite of the requirement of high transmittance. The best efficiency (5.14%) is achieved with FTO films having a 34.2% transmittance and a 3.27 Ω □–1 sheet resistance, outperforming standard FTO films (4.74%) with a 10 Ω □–1 sheet resistance and an ∼83% transmittance. The results indicate that the transparency of FTO is not a dominant factor and carefully controlled light scattering and electrical properties in translucent FTO films would lead to the realization of dye-sensitized solar cells that deliver superior efficiency.

Study of fluorine-doped tin oxide thin films deposited by pneumatic spray pyrolysis and ultrasonic spray pyrolysis: a direct comparison

A comparative analysis was performed of fluorine-doped tin oxide (FTO) thin films deposited through two different systems: pneumatic spray pyrolysis and ultrasonic spray pyrolysis. The films were deposited on glass substrates at 460 °C, with varying weight ratios of fluorine to tin (F/Sn = 0.35, F/Sn = 0.50, and F/Sn = 0.65). The investigation focuses on the evolution of the film’s crystallinity, structural, morphological, transmittance, optical, and electrical properties. Resonant nuclear reaction (RNR) and energy dispersive spectroscopy (EDS) techniques were used to confirm the presence of fluorine in the FTO samples. The results show that the sample with F/Sn = 0.50 deposited through pneumatic spray pyrolysis, with a figure of merit of 34.5 × 10−3 Ω−1, exhibits the best characteristics for use as electrodes in optoelectronic devices, particularly in the fabrication of solar cells.

FTO Thin Films: Outcome of Substrate Temperature on the Structural and Optical Properties

In this work, Fluorine doped Tin Oxide (FTO) thin films are effectively deposited by JNSP technique using ammonium fluoride and tin chloride as solution composition. The influence of Substrate Temperature (ST) on the structural and optical properties of FTO thin films is investigated. XRD pattern authenticates the presence of single phase polycrystalline orthorhombic structure with favored orientation along (230) and (200) directions. The sharp band obtained between 475 and 700 cm-1 originated from asymmetric stretching vibrations of metal oxide (SnO2:F). The highest band gap energy was obtained as 3.57 eV at 425°C and lowest band gap energy was obtained as 3.49 eV at 450°C obtained from UV-Vis spectra.

Design of experiments optimization of fluorine-doped tin oxide films prepared by spray pyrolysis for photovoltaic applications

Transparent conducting oxides (TCOs) have witnessed an ever-expanding use in our lives through many optoelectronic applications, namely photovoltaic (PV) devices. Indium-tin oxide (ITO) is the most used and studied TCO, but it lacks thermal and chemical stability and indium is a scarce and toxic element. Fluorine-doped tin oxide (FTO) emerged as the most promising alternative to ITO, presenting better thermal and chemical stability. Among the numerous techniques for depositing FTO thin films over glass substrates, spray pyrolysis is the simplest and most economical, with great potential for upscaling. However, the relative importance of the experimental variables that influence the optoelectronic properties remains barely addressed. Following this premise, the present work aimed at optimizing the deposition of FTO films on soda lime glass (SLG) substrates by spray pyrolysis following a Design of Experiments (DoE) methodology. The optoelectronic properties of FTO-SLG substrates was evaluated based on their optical transmittance and sheet resistance, both combined in a figure of merit (FoM) tailored for PV applications. It was concluded that the volume of sprayed solution and the fluorine/tin ratio in the precursor have the greatest influence in the FoM, being the optimal deposition conditions a sprayed volume of 60.8 ml and a [F]/[Sn] ratio of 0.45. FTO-SLG substrates prepared with these conditions achieved a FoM of 0.680 Ω□−1/10, corresponding to a sheet resistance of 3.40 Ω□ and a transmittance equivalent to 77% of the maximum current generated in the considered spectrum. The improved FoM was validated in dye-sensitized and perovskite solar cells (DSSCs and PSCs, respectively), assembled with in-house optimized and commercial substrates. The efficiency of DSSCs was improved by 8.9% (relative), whereas PSCs achieved a light-to-power efficiency of 17% (absolute), corresponding to an improvement of 4.7% (relative).

Smartphone-based dynamic measurements of electro-optically modulated lossy-mode resonance and its biosensing applications

In this work, we discuss an application of a smartphone-based spectrometer for dynamic analysis of optical response of an electro-optically modulated lossy-mode resonance (LMR) optical fiber sensor. The LMR was achieved when a section of a multimode optical fiber core was coated with a fluorine-doped tin oxide (FTO) thin film. The FTO, thanks to its electrical properties, has been simultaneously applied as an electrochemical electrode. It has been shown that when an electrical potential is applied to the obtained dual-domain sensor, the distribution of charge carriers in the FTO changes and it can be dynamically measured optically using the smartphone-based spectrometer with a time resolution below 0.5 s. Moreover, when charge carriers' accumulation is induced at the FTO surface, the changes on the sensor surface, such as biomaterial binding, can be identified with the device. The optical label-free biosensing performance of the system has been verified using streptavidin and green fluorescent protein (GFP) as receptor and target, respectively. The outcome of optical and electrical measurements, acquired simultaneously, were compared. It has been found that the system can detect concentration of GFP as low as 1 ng/mL. It must be noted that the smartphone-based dynamic optical measurements were possible with only the device, a low-cost detachable adapter, and a custom-made software application. Electrical measurements using a smartphone with such low-cost modifications are hardly possible. The setup can be further simplified using just a battery for setting the potential difference, thus establishing electro-optical modulation of the sensor. Such a system may be considered as suitable for a broad spectrum of sensors and their label-free biosensing applications.

Etching characteristics and surface properties of fluorine-doped tin oxide thin films under CF4-based plasma treatment

Etching characteristics and surface properties of fluorine-doped tin oxide thin films under CF4-based plasma treatment

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.

Effective Recycling Method for Silicon Photovoltaic Modules With Electrical Sacrificial Layer

Several countries have shown interest in the development of methods for recycling photovoltaic (PV) modules because the number of end-of-life modules is expected to increase owing to the increasing use of PV modules. Generally, physical, chemical, and thermal (incineration) methods are used for separating glass from the PV module when the end-of-life modules are recycled. In the physical method, the ethylene vinyl acetate (EVA) is cut using a heated knife or wire, whereas in the chemical method, the EVA is dissolved using chemicals. Among the treatment methods, the thermal method is widely used, wherein EVA is burned at high temperatures. In this article, a structure wherein a sacrificial layer is located between the front glass and EVA is proposed. Herein, a fluorine-doped tin oxide (FTO) thin film was used as a sacrificial layer and was delaminated using transparent conductive oxide corrosion assisted by voltage and moisture in a thin-film solar cell, after which the front glass was easily separated from the EVA. The experiment proceeded by delaminating the FTO thin film deposited on the front glass and separating EVA from the front glass. Finally, after creating a minimodule structure, the front glass was released from the EVA.

Functional fluorine-doped tin oxide coating for opto-electrochemical label-free biosensors

Sensors operating in multiple domains, such as optical and electrochemical, offer properties making biosensing more effective than those working in a single domain. To combine such domains in one sensing device, materials offering a certain set of properties are required. Fluorine-doped tin oxide (FTO) thin film is discussed in this work as functional optically for guiding lossy modes and simultaneously electrochemically, i.e. as a conductive material for a working electrode. Performance of the FTO-based optical fiber lossy-mode resonance (LMR) sensor in both optical and electrochemical domains is analyzed. Additionally, to enhance applicability of the sensor, its probe-like reflection configuration has been developed. It is found that FTO may be considered as a promising alternative for other thin conductive oxides (TCO), such as indium tin oxide (ITO) that has been often applied up to date in various dual-domain sensing concepts. In the optical domain, the sensitivity of the FTO-LMR sensor to external refractive index (RI) has reached 450 nm/RIU in the RI range of 1.33–1.40 RIU. In the electrochemical domain, in turn, the response for FTO electrode in 1,1′-Ferrocenedimethanol solution has been reached with RedOx current low peak-to-peak separation. In contrast to the ITO-LMR sensors, the FTO-LMR counterparts exhibit a significant influence of applied potential on LMR wavelength shift in a wide potential range. It is shown using streptavidin as a target biomaterial that label-free biosensing applications of the FTO-LMR approach are possible. The dual-domain functionality allows for cross-verification between readouts received in both the domains, as well as enhancement of optical sensitivity when cross-domain interactions are applied.

Effects of sub-picosecond direct laser interference patterning on the optoelectronic properties of fluorine-doped tin oxide thin films

An increase in the angular spread of incident light was obtained in FTO thin films after the generation of periodic micro- and nano-structures with infrared sub-picosecond Direct Laser Interference Patterning.

Effects of 7 MeV proton irradiation on microstructural, morphological, optical, and electrical properties of fluorine-doped tin oxide thin films

Effects of 7 MeV proton irradiation on microstructural, morphological, optical, and electrical properties of fluorine-doped tin oxide thin films

Evolution of defects and charge carrier transport mechanism in fluorine-doped tin oxide thin films upon thermal treatment

Fluorine-doped tin oxide (FTO) thin films were prepared by a radio frequency magnetron sputtering technique. The defects and charge carrier transport behavior in FTO thin films were evaluated during the transition process from amorphous to nanocrystalline structures. The stable lattice structure in FTO thin films was obtained as the annealing temperature reached 400 °C. Positron annihilation results indicated that defect evolution in the FTO thin films was shown in two stages, formation and reduction of vacancies/vacancy clusters. The carrier mobility of the FTO thin films annealed at 600 °C was enhanced twice the amount than that of the unannealed samples. The correlation between the results obtained from positron annihilation and the Hall effect revealed the importance of defect scattering in deciding the charge carrier mobility. A defect scattering mechanism was proposed to interpret the noticeable increment of carrier mobility in FTO thin films after thermal treatment.

Dye-Sensitized Solar Cell for Building-Integrated Photovoltaic (BIPV) Applications

One of the important research directions in the field of photovoltaics is integration with construction. The integration of solar cell systems with a building can reduce installation costs and help optimize the used space. Among the few literature reports on photovoltaic roof tiles, solutions with silicon and thin film solar cells dominate. An interesting solution may be the application of dye-sensitized solar cells. In addition to their interesting properties, they also have aesthetic value. In the classic arrangement, they are constructed using glass with a transparent conductive layer (TCL). This article describes replacing a classic glass counter electrode with an electrode based on a ceramic tile and nickel foil. First, a continuous and homogeneous fluorine-doped tin oxide (FTO) thin film was developed so that the above-mentioned substrate could be applied. The atomization method was used for this purpose. Then, nanocolloidal platinum paste was deposited as a catalytic material using the screen printing method. The electrical parameters of the manufactured DSSCs with and without a counter electrode tile were characterized by measuring their current–voltage characteristics under standard AM 1.5 radiation. A dye-sensitized solar cell integrated with ceramic tiles and nickel foil was produced and displayed an efficiency of over 4%. This solution makes it possible to expand their construction applications. The advantage of this solution is full integration with construction, while simultaneously generating electricity. A dye-sensitized solar cell was built layer-by-layer on a ceramic tile and nickel foil.

Influence of texture coefficient on the electrical properties of spray-deposited fluorine-doped tin oxide thin film

Fluorine-doped tin oxide (FTO) thin films were deposited onto a glass substrate using the spray pyrolysis technique, and the substrate temperature was varied from 450 to 550 °C with steps of 25 °C. A considerable change was observed for the texture, which was found to be influential on the morphological and electrical characteristics of the FTO thin films. Although the FTO film deposited at 450 °C was highly textured along the (200) orientation, a considerable reduction was observed for TC(200) after 500 °C. On the contrary, the TC(301) and TC(200) started to grow by increasing the substrate temperature to the extent of being the completely dominant planes at 550 °C. As a result, the mobility of the films met a constant reduction from 24.20 cm2 V−1 s−1 for 450 °C to 11.40 cm2 V−1 s−1 for 550 °C. The carrier concentration reached its maximum at 500 °C (3.86 × 1020 cm−3) and declined with a further increase of the deposition temperature. The best resistivity of 8.25 × 10−4 Ω cm corresponding to a 16 Ω/sq sheet resistance and average transmittance of 85.32% was achieved at 500 °C. The aforementioned results led to a considerable figure of merit of 12.8 × 10−3 Ω−1 which is indicative of a high-quality spray-deposited FTO thin film.

Controller of fluorine­doped tin oxide thin films deposition via cycles and annealing temperatures by spin coating techniques

Fluorine-doped tin oxide (FTO) thin films have been deposited by the modified spin coating method at 3000 rpm using tin (II) chloride dehydrate (SnCl 2 ×2H 2 O) as a precursor, ammonium fluoride (NH 4 F) as a dopant and ethanol as a solvent. The aim of this research is to find out the quality of the thin film based on the number of cycles (3, 4, 5, and 6 cycles) and annealing temperature (300, 400 and 500 °C). The variation of annealing temperature and number of cycles can affect the crystal structure of the FTO thin film, crystal size and grain size. Increasing the number of cycles and annealing temperature can lead to larger crystallite size and lower dislocation density, so that electrons between the grains can move easily. The large grain can reduce the grain boundary, increasing the electron mobility and decreasing the resistivity. XRD analysis shows that the structure of SnO 2 polycrystalline with the most dominant crystal plane (110) is formed in this research when compared to the intensity of other structures. The resistivity value decreases with increasing the annealing temperature and number of cycles. In addition, transparency value also decreases along with increasing the annealing temperature and number of cycles. The optimum results of resistivity and transparency values obtained in this research are 1.692´10 -2 Ω×cm and 69.232 % at 500 °C and 5 cycles. These results can be used as a reference for further study to optimize the production of fluorine-doped tin oxide (FTO) thin film with spin coating. Therefore, many factors that affect the production of fluorine-doped tin oxide (FTO) thin film, either dissolving stage or deposition process on the substrate surface still need to be studied deeply to obtain the optimum result

Realization of highly conducting and transparent SnO2 thin films by optimizing F/Sn molar ratio for electrochemical applications

In the present work, fluorine-doped and undoped tin oxide thin films were deposited on microscopic glass substrate by nebulized spray pyrolysis technique at a constant substrate temperature of 350 °C. The influence of fluorine doping on the physical properties of tin oxide has been investigated by depositing the films by varying the F/Sn precursor molar ratio. The structural, morphological, chemical, optical and electrical properties of the films were characterized by X-ray diffractometer, transmission electron microscope, selected area electron diffraction, field emission scanning electron microscope, X-ray photoelectron spectroscopy, ultraviolet visible near infrared spectroscopy, and Hall effect measurements. The results suggest that deposited films are well adhered and uniformly deposited on the substrate. The structural analysis exhibit that the films are highly polycrystalline, crystallized in tetragonal structure with preferred orientations perpendicular to (200), (211) and (110) planes, and without any secondary phases. Optical transmittance greater than 75% in the visible region is obtained with an optical bandgap energy lying in the range 3.98 – 4.07 eV. Minimum resistivity, for optimized fluorine doped on tin oxide thin films, was in the range of 9.002×10−4 Ω-cm at room temperature. Hall Effect measurements show that the fluorine-doped films are degenerate semiconductors with n-type electrical conductivity. The analysis results show that device quality, highly transparent and stable fluorine doped tin oxide thin films which are having least resistivity values for the minimum doping concentration of 6.1% of fluorine can be prepared by nebulizer spray pyrolysis technique.

Effects of low-dose γ-irradiation on the structural, morphological, and optical properties of fluorine-doped tin oxide thin films

This paper presents the effects of low-dose γ-irradiation on the structural, morphological, and optical properties of Fluorine-doped tin oxide (FTO) thin films for application as a passive thermal control coating in future miniaturized lightweight spacecraft. Commercial-grade FTO films on glass substrate (Pilkington Ltd, UK) with a bulk density of 2.5 g/cm3, sheet resistance of 12 Ω.sq-1, coating thickness of 450 nm, optical band-gap of 3.80 eV, a carrier concentration of 1.50×1020 cm−3 and a mobility of 15 cm2/Vs were irradiated at room temperature and atmospheric pressure using a 60Co gamma source (with gamma energies of 1.17 MeV and 1.33 MeV) at iThemba Laboratory for Accelerator Based Sciences, Cape Town, South Africa. Each sample was exposed to γ-rays for a different span of time to achieve a series of different integrated absorbed doses of 20, 30, and 50 Gy, at a dose rate of 0.207 Gy/min. Evolution in structural properties of the films was characterized using a Bruker AXS D8 Advance XRD with Cu-Kα (λ = 1.54056 Å) scanned in the 2θ degree range of 20 – 80 degrees. Surface properties were analyzed using a VEECO Dimension 1100 AFM machine. Meanwhile, variations in optical transmittance of the films was investigated using a Cary 5000 UV-vis-NIR spectrophotometer of Varian, Inc. model internal DRA- 2500 in the wavelength range of 200 – 2500 nm. XRD results indicate an enhancement of crystallization after irradiation, slight peak shifts, and variations in crystallite sizes with increasing dose. Surface roughness decreased with increasing dose and the grain structures also seen to vary with dose. No significant variations in optical transmittance of the FTO films.

Opto-electronic properties of cerium-doped FTO thin films prepared using Nebulizer spray technique for TCO application

Nebulizer spray pyrolysis, a facile thin film deposition method was adopted to fabricate pristine fluorine-doped tin oxide (FTO) and cerium (Ce) doped FTO films. Structure-opto-electronic nature have been analyzed for the prepared films. X-Ray diffraction shows the tetragonal and polycrystalline nature with decrease in size of the crystallite on increasing Ce concentration. Raman spectral analysis exhibited Raman active mode, IR active mode and stretching vibration mode of Sn-O2 band. Smoothness of the film was increased with increasing doping concentration confirmed from AFM study. Photoluminacence (PL) analysis exposed the band edge and blue/green emissions in UV and visible regions. Transmittance of the films were increased with rising the doping concentration of Ce and highest transmittance of 81% was obtained for 1.5 wt.% Ce. Bang gap value was increased from 3.90 eV to 4.00 eV for pristine to 1.5 wt.% Ce doped film. High conductivity and carrier concentration were obtained for the doped films. The maximum figure of merit 3.2 × 10-3 Ω-1 was noted for 1.5 wt.% Ce doped film. Since the prepared film has highest transmittance and electrical conductivity, this may perform as an TCO material in optoelectronics.