Fluorine-doped SnO2 Thin Films Research Articles

Solvent effect on the optoelectronic properties of fluorine doped SnO2 thin films prepared by spray-pyrolysis

This work explores the effects of choice of solvent on the optoelectronic properties of spray-pyrolyzed fluorine (F)-doped tin oxide (SnO2) thin films deposited on glass substrates over an area of 5 × 5 cm2. A 2-methoxyethanol (C3H8O2) and ethylene glycol (C2H6O2) admixture in varying proportions is used as solvent. The volume of C2H6O2 is varied as 0, 25, 50, and 100 ml in the above admixture. The XRD patterns reveal successful formation of tetragonal SnO2 lattice without any structural change. Upon changing the volume of C2H6O2 in C3H8O2, the textured growth changes from (110) direction to (211) direction. The film thickness is found to vary significantly with varying volume of the mixed solvents. Transmittance is found to increase and reach a maximum value of 75% (at 550 nm) for the film deposited with only C2H6O2. The photoluminescence emission data reveals that the overall intensity of violet emission is found to quench upon increasing the volume of C2H6O2. The sheet resistance is found to decrease gradually with increasing volume of C3H8O2 and is found to be the lowest with a value of 6.34 Ω/□ for complete 100 ml of C3H8O2. The surface wettability nature of the thin films obtained from contact angle measurements indicate changeover from hydrophobic to hydrophilic nature (104.4° to 52.2°) with increasing C2H6O2 vol in the admixed solvent. Among all these samples, the film prepared with 100% C2H6O2 solvent shows highest figure of merit value of 3.02×10–3 Ω–1. The optimal film prepared with complete C2H6O2 solvent has surface work function of 4.69 eV and shows highest power conversion efficiency of 2.21% when used in a dye-sensitized solar cell compared to devices fabricated using other admixed solvents. In the solvent admixture, higher volume of C3H8O2 is beneficial for obtaining low sheet resistance, whereas higher volume of C2H6O2 leads to high transmittance, thereby permitting to fix the solvent concentration based on the need for optical transparency and electrical sheet resistance as per custom requirements for a specific optoelectronic application.

Properties of fluorine-doped SnO2 thin films by a green sol–gel method

Fluorine doped tin oxide (FTO) films were fabricated on a glass substrate by a green sol–gel dip-coating process. Non-toxic SnF2 was used as fluorine source to replace toxic HF or NH4F. Effect of SnF2 content, 0–10mol%, on structure, electrical resistivity, and optical transmittance of the films were investigated using X-ray diffraction, Hall effect measurements, and UV–vis spectra. Structural analysis revealed that the films are polycrystalline with a tetragonal crystal structure. Grain size varies from 43 to 21nm with increasing fluorine concentration, which in fact critically impacts resultant electrical and optical properties. The 500°C-annealed FTO film containing 6mol% SnF2 shows the lowest electrical resistivity 7.0×10−4Ωcm, carrier concentration 1.1×1021cm−3, Hall mobility 8.1cm2V−1s−1, optical transmittance 90.1% and optical band-gap 3.91eV. The 6mol% SnF2 added film has the highest figure of merit 2.43×10−2Ω−1 which is four times higher than that of un-doped FTO films. Because of the promising electrical and optical properties, F-doped thin films prepared by this green process are well-suited for use in all aspects of transparent conducting oxide.

In Situ Incorporation of Pt Nanoparticles in Fluorine-doped SnO2 Nanocomposite Thin Films by a One-step Synthesis

Abstract Incorporation of one-step-synthesized Pt nanoparticles (NPs) enhanced the electrical properties of direct-patternable fluorine (1.06 atom %)-doped SnO2 thin films without significant degeneration of the structural or optical properties. A fluorine-doped SnO2 thin film with 0.5 atom % Pt NPs showed slightly lower electrical resistivity than the pristine fluorine-doped SnO2 thin film due to the larger positive contribution of the reduction-catalytic effect of Pt NPs than the negative contribution from halide bond formation between fluorine ions and Pt NPs. However, above 0.5 atom % Pt NPs incorporation, the electrical resistivity of the fluorine-doped SnO2 thin film increased because the effects caused by halide bond formation are greater than those of the reduction-catalytic effect. Direct-patterning of fluorine-doped SnO2 thin films, after spin coating, was successfully performed with a line width of 60 µm.

High Performance ZnO-SnO2:F Nanocomposite Transparent Electrodes for Energy Applications

Enhancing the propagation length of light without sacrificing the electro-optical properties of transparent electrodes is of particular interest to solar cells for reaching higher efficiency. This can typically be achieved by nanostructured electrodes but all too often at the expense of complexity and cost-effectiveness. In this work, we demonstrate the simple and low-cost fabrication of a new type of ZnO-SnO2:F nanocomposite thin film by combining spin-coated ZnO nanoparticles on glass with fluorine-doped SnO2 thin films deposited by atmospheric spray pyrolysis. The resulting nanocomposites exhibit a dual surface morphology featuring rough ZnO-SnO2:F nanostructures along with the original smooth SnO2:F thin film. By readily modulating the surface morphology of ZnO-SnO2:F nanocomposite thin films with the initial ZnO NP surface coverage, the scattering efficiency of the incident light can remarkably be controlled over the 400-1100 nm solar spectrum wavelength range. High quality hazy ZnO-SnO2:F thin layers are therefore formed with an averaged haze factor ranging from 0.4 to 64.2% over the 400-1100 nm solar spectrum range while the sheet resistance is kept smaller than 15 Ω/sq for an average total optical transmittance close to 80%, substrate absorption and reflection included. Eventually, optical simulations using Fourier transform techniques are performed for computing the obtained haze factors and show good agreement with experimental data in the 400-1100 nm solar spectrum wavelength range. This opens up additional opportunities for further design optimization of nanoengineered transparent electrodes.

Enhanced preferential orientation and electrical property of fluorine-doped SnO2 thin films via barrier layer

Polycrystalline fluorine-doped SnO2 thin films with SiCxOy or SixSnyO2 barrier layer are deposited on glass substrates by atmospheric pressure chemical vapor deposition (APCVD) method. The effect of barrier layer on structure and electrical property of FTO films was investigated. Results show that the inserting of barrier layer, especially the SiCxOy layer, has led to the improved crystallinity and the enhanced preferential orientation along the (200) crystallographic plane. SnO2:F/SiCxOy/Glass films with larger grain size and a columnar growth structure exhibited lower resistivity (~4.9×10−4), higher reflectance in the mid-far-infrared region (~80%) and lower emissivity (0.16), while maintaining high transmittance in the visible range. The SiCxOy film has therefore been considered as a more ideal potential barrier layer for FTO thin film production.

Optical and Structural Characterization of Fluorine-Doped SnO2 Thin Films Prepared by Spray Ultrasonic

Optical and Structural Characterization of Fluorine-Doped SnO2 Thin Films Prepared by Spray Ultrasonic

Electron scattering mechanisms in fluorine-doped SnO2 thin films

Polycrystalline fluorine-doped SnO2 (FTO) thin films have been grown by ultrasonic spray pyrolysis on glass substrate. By varying growth conditions, several FTO specimens have been deposited and the study of their structural, electrical, and optical properties has been carried out. By systematically investigating the mobility as a function of carrier density, grain size, and crystallite size, the contribution of each physical mechanism involved in the electron scattering has been derived. A thorough comparison of experimental data and calculations allows to disentangle these different mechanisms and to deduce their relative importance. In particular, the roles of extended structural defects such as grain or twin boundaries as revealed by electron microscopy or x-ray diffraction along with ionized impurities are discussed. As a consequence, based on the quantitative analysis presented here, an experimental methodology leading to the improvement of the electro-optical properties of FTO thin films is reported. FTO thin films assuming an electrical resistivity as low as 3.7 · 10−4 Ω cm (square sheet resistance of 8 Ω/◻) while retaining good transmittance up to 86% (including substrate effect) in the visible range have been obtained.

Fluorine-doped SnO2 thin films deposited on polymer substrate for flexible transparent electrodes

Fluorine-doped SnO2 (FTO) thin films are deposited by ultrasonic spray pyrolysis on preheated polyimide (PI) substrates. Their structural, electro-optical and electro-mechanical properties are investigated versus both growth temperature and film thickness. FTO thin films exhibit textured columnar grain morphology and preferred orientations along the <101>, <301>, <211> and <200> are favored depending on growth temperature and film thickness. The films deposited on PI substrate at 380°C present the best compromise in terms of electro-optical properties with a low electrical resistivity of 8.9×10−4Ωcm, a mobility of 17.9cm2/V·s combined with an optical transmittance up to 79.4% at 780nm. Eventually, a figure of merit of 2.3×10−3Ω−1 is obtained. The electro-mechanical properties are studied during controlled fatigue testing and analyzed according to the energy-based Griffith's criterion.

Preferential orientation of fluorine-doped SnO2 thin films: The effects of growth temperature

Polycrystalline fluorine-doped SnO2 thin films with a given thickness of about 250nm have been grown by ultrasonic spray pyrolysis with a growth temperature in the range of 360–480°C. A texture transition from 〈101〉 to 〈100〉 and 〈301〉 crystallographic orientations has experimentally been found by X-ray diffraction measurements as growth temperature is raised, revealing that a process of abnormal grain growth has occurred. The texture effects have been investigated within a thermodynamic approach considering that grain growth is driven by the minimization of total free energy. The anisotropic character of the physical quantities and the effects of growth temperature have been shown both on the surface energy per unit volume through its dependence on the oxygen chemical potential and on the strain energy density through its variation with the elastic strain and biaxial modulus. Importantly, it is demonstrated by thermodynamic simulations that the oxygen chemical potential increases with growth temperature in the spray pyrolysis conditions, showing that the atmosphere is less and less reducing. For low growth temperature, it is revealed that the 〈101〉 preferred orientation is due to surface energy minimization since the (101) reduced surfaces have a surface energy lower than the (100) reduced surfaces. In contrast, as growth temperature is raised, the 〈100〉 crystallographic orientation becomes predominant owing to strain energy minimization. A texture map is finally determined, revealing the expected texture as a function of elastic strain and oxygen chemical potential.

Thickness effects on the texture development of fluorine-doped SnO2 thin films: The role of surface and strain energy

Polycrystalline fluorine-doped SnO2 thin films have been grown by ultrasonic spray pyrolysis with a thickness varying in the range of 40 to 600 nm. A texture transition from ⟨110⟩ to ⟨100⟩ and ⟨301⟩ crystallographic orientations has experimentally been shown by x-ray diffraction measurements as film thickness is increased, showing that a process of abnormal grain growth has occurred. The texture effects are considered within a thermodynamic approach, in which the minimization of total free energy constitutes the driving force for grain growth. For very small film thickness, it is found that the ⟨110⟩ preferred orientation is due to surface energy minimization, as the (110) planes have the lowest surface energy in the rutile structure. In contrast, as film thickness is increased, the ⟨100⟩ and ⟨301⟩ crystallographic orientations are progressively predominant, owing to elastic strain energy minimization in which the anisotropic character is considered in the elastic biaxial modulus. A texture map is eventually determined, revealing the expected texture as a function of elastic strain and film thickness.

Structural analysis of monolayered and bilayered SnO2 thin films

Mono- and bilayered undoped and fluorine doped SnO2 thin films have been successfully prepared at optimized postdeposition temperatures of 590 and 610°C by the atmospheric pressure chemical vapor deposition method. The microstructural properties of as-deposited films were thoroughly examined using the Rietveld refinement of powder-like XRD patterns, while the film surface has been probed using atomic field microscopy. The structural parameters were correlated to the deposition parameters and interesting findings were revealed. Finally, the specific electrical resistivity of the thin films has been measured and correlated with the optical transmittance.

Characteristic of Low Resistivity Fluorine-Doped SnO2 Thin Films Grown by Spray Pyrolysis

Transparent conducting oxide films of fluorine-doped SnO2 (FTO) were deposited on glass substrates by spray pyrolysis in order to determine the effect of spray solution concentration. These films were prepared with different F-doping concentrations from 0 to 33 mol %. The films were all polycrystalline with tetragonal crystal structures. The best electro-optic properties were achieved with a fluorine doping concentration of 17 mol % at a substrate temperature of 500 °C. These conditions resulted in a film with an average transmittance of 82%, a resistivity of 4.0 ×10-4 Ω cm, a carrier concentration of 4.7 ×1020 cm-3 and a mobility of 34 cm2 V-1 s-1.

Dispersion of resonant Raman peaks of CO and OH in SnO2, Mo1−xFexO2 thin films and SiO2 bulk glass

Resonance Raman (RR) peaks of CO and OH stretching modes and their higher harmonics have been observed superimposed on the photoluminescence (PL) spectrum of SnO2 thin films. Commercial fluorine doped SnO2 thin films deposited by sputtering on glass and SnO2 thin films deposited on Si by laser ablation have been studied. The dispersions of CO and OH stretching RR modes are ∼600 cm−1 eV−1 and 800 cm−1 eV−1, respectively. The dispersion of the third harmonic of the CO stretching mode is ∼2000 cm−1 eV−1. Similar dispersion of the RR peak of CO stretching modes and higher harmonics superimposed on PL spectra has been observed in Mo1−xFexO2 thin films and SiO2 bulk glass. Large dispersion of RR peaks seems to be a common property of oxides with impurities of CO and OH.

Thermoelectric power of SnO2 anisotropic thin films

A calculation of thermoelectric power in fluorine-doped SnO2 thin films is carried out using the Boltzmann transport theory and including anisotropic effects over material as well as the degeneracy grade of the samples. Curves of thermoelectric power in dependence of the temperature and concentration of F-impurities are reported. Finally, the computed values are compared with those obtained experimentally.

Atmospheric pressure deposition of fluorine-doped SnO2 thin films from organotin fluorocarboxylate precursors

Nine organotin fluorocarboxylates R n SnO 2 CR f (n = 3, R = Bu, R f = CF 3 , C 2 F 5 , C 3 F 7 , C 7 F 15 ; R = Et, R f = CF 3 , C 2 F 5 ; R = Me, R f = C 2 F 5 ; n = 2, R = Me, R f = CF 3 ) have been synthesized; key examples have been used to deposit fluorine-doped SnO 2 thin films by atmospheric pressure chemical vapour deposition. Et 3 SnO 2 CC 2 F 5 , in particular, gives high-quality films with fast deposition rates despite adopting a polymeric, carboxylate-bridged structure in the solid state, as determined by X-ray crystallography. Gas-phase electron diffraction on the model compound Me 3 SnO 2 CC 2 F 5 shows that accessible conformations do not allow contact between tin and fluorine, and that direct transfer is therefore unlikely to be part of the mechanism for fluorine incorporation in SnO 2 films. The structure of Me 2 Sn(O 2 CCF 3 ) 2 (H 2 O) has also been determined and adopts a trans-Me 2 SnO 3 coordination sphere about tin in which each carboxylate group is monodentate.

Atmospheric pressure chemical vapour deposition of fluorine-doped tin(IV) oxide from fluoroalkyltin precursors

Perfluoroalkytin compounds R(4−n)Sn(Rf)n (R = Me, Et, Bu, Rf = C4F9, n = 1; R = Bu, Rf = C4F9, n = 2, 3; R = Bu, Rf = C6F13, n = 1) have been synthesized, characterized by 1H, 13C, 19F and 119Sn NMR, and evaluated as precursors for the atmospheric pressure chemical vapour deposition of fluorine-doped SnO2 thin films. All precursors were sufficiently volatile in the range 84–136 °C and glass substrate temperatures of ca 550 °C to yield high-quality films with ca 0.79–2.02% fluorine incorporation, save for Bu3SnC6F13, which incorporated <0.05% fluorine. Films were characterized by X-ray diffraction, scanning electron microscopy, thickness, haze, emissivity, and sheet resistance. The fastest growth rates and highest quality films were obtained from Et3SnC4F9. An electron diffraction study of Me3SnC4F9 revealed four conformations, of which only the two of lowest abundance showed close F Sn contacts that could plausibly be associated with halogen transfer to tin, and in each case it was fluorine attached to either the γ- or δ-carbon atoms of the Rf chain. Copyright © 2005 John Wiley & Sons, Ltd.