Fluorine-doped Tin Oxide Layer Research Articles

Can fluorine-doped tin Oxide, FTO, be more like indium-doped tin oxide, ITO? Reducing FTO surface roughness by introducing additional SnO2 coating

Abstract

Sequential Preparation of Dual‐Layer Fluorine‐Doped Tin Oxide Films for Highly Efficient Perovskite Solar Cells

A dual-layer fluorine-doped tin oxide (FTO) film has been fabricated by means of sequential spray pyrolysis for high-efficiency perovskite solar cells (PSCs). The H-FTO/L-FTO dual layer film consists of a H-FTO layer prepared at high deposition temperature (≈450 °C) and a L-FTO layer, fabricated at low deposition temperature (≈150 °C), which is used to replace the traditional compact TiO2 /FTO layer. The effects of F/Sn molar ratio, precursor solution concentration, and deposition temperature on the electrical, optical, surface morphological, and grain structural characteristics of H-FTO layers have been studied systematically. With an increase in precursor solution concentration, the mobility and carrier concentration of H-FTO increases; however, the grain size and sheet resistance decreases as the precursor solution concentration increases. A high deposition temperature results in a large grain size and enhanced haze value. The L-FTO layer expresses compact layer growth, inconsistent with the H-FTO surface structure, and possesses excellent electron collection and transport efficiency. The effect of the hole-blocking characteristics of L-FTO on the PSC performance is studied. This study provides a novel dual-layer FTO film to replace the traditional compact TiO2 /FTO layer, which is usually prepared by coating TiO2 precursor on FTO following calcination at 450 °C. The H-FTO/L-FTO dual-layer film can simplify the fabrication process and maintain a high power conversion efficiency (PCE); this results in more efficient electron transportation and blocking of holes. The champion device of PSCs with H-FTO/L-FTO shows the highest PCE of 17.37 % under the illumination of 100 mW cm-2 (AM1.5G).

Synthesis of Polymeric Carbon Nitride Films with Adhesive Interfaces for Solar Water Splitting Devices

Polymeric carbon nitride (PCN) films are synthesized for solar water splitting devices. Herein, five precursors and their mixtures are attempted, achieving PCN films in ca. 40 different morphologies. We find that sulfur (S) containing and non-S precursors must be mixed to grow PCN films on fluorine doped tin oxide (FTO) glasses. Through the investigations of the PCN films, S is found to only exist at the interfaces between the PCN and FTO films. In this case, S acts not only as the initialization for the growth of the PCN films but also as connections to assist charge migration for water splitting devices. As a result, the best performance ca. 100 μA/cm2 is achieved at 1.23 VRHE under AM 1.5 illumination in NaOH electrolyte solution without sacrificial agent. This result can be attributed to the reduced defects along the interfaces and the lessened charge recombination. This synthesis of PCN films with the improved chemical adhesion to the FTO layer envisages such organic material for the construction of other flexible functional devices.

Influence of Charge Transport Layers on Open-Circuit Voltage and Hysteresis in Perovskite Solar Cells

Summary Perovskite materials have experienced an impressive improvement in photovoltaic performance due to their unique combination of optoelectronic properties. Their remarkable progression, facilitated by the use of different device architectures, compositional engineering, and processing methodologies, contrasts with the lack of understanding of the materials properties and interface phenomena. Here we directly target the interplay between the charge-transporting layers (CTLs) and open-circuit potential ( V OC ) in the operation mechanism of the state-of-the-art CH 3 NH 3 PbI 3 solar cells. Our results suggest that the V OC is controlled by the splitting of quasi-Fermi levels and recombination inside the perovskite, rather than being governed by any internal electric field established by the difference in the CTL work functions. In addition, we provide novel insights into the hysteretic origin in perovskite solar cells, identifying the nature of the contacts as a critical factor in defining the charge accumulation at its interface, leading to either ionic, electronic, or mixed ionic-electronic accumulation.

Novel nanostructured electron transport compact layer for efficient and large-area perovskite solar cells using acidic treatment of titanium layer

A new method for the deposition of a pinhole-free compact layer of TiO2 is introduced for the development of efficient perovskite solar cells. Acidic treatment of titanium layer (ATTL), deposited by rotational magnetron sputtering, presents a compact pinhole-free TiO2 thin film. Deposition of a compact TiO2 thin film on fluorine-doped tin oxide layers by ATTL did not change the surface roughness. To compare the introduced method, perovskite solar cell devices were fabricated and studied using different methods for the deposition of the TiO2 compact layers, which were used as common compact layer deposition methods. The ATTL method proposed considerable photovoltaic enhancement of perovskite solar cell performance (at least 22% enhancement in this work) by reducing the pinholes and sheet resistance of the TiO2 thin film. The improvement in the open-circuit voltage and the fill factor of the prepared devices using the ATTL method strongly confirmed the nature of the deposited pinhole-free TiO2 thin film. This method is shown to be an appropriate route for the reliable large-scale deposition of TiO2 compact layers.

Experimental Analysis on the Molten-Phase Dewetting Characteristics of AuPd Alloy Films on Topographically-Structured Substrates

AuPd nanoparticles are formed on fluorine-doped tin oxide (FTO) by a nanosecond laser irradiation-induced dewetting process of deposited AuPd films. In particular, we analyze the effect of the surface topography of the substrate on the dewetting process and, so, on the final mean size of the formed nanoparticles. In fact, we used two supporting FTO substrates differing in the surface topography: we used a FTO layer which is un-intentionally patterned since it is formed by FTO pyramids randomly distributed on the glass slide as result of the deposition process of the same FTO layer, namely substrate A. We used, also, a further FTO substrate, namely substrate B, presenting, as a result of a chemical etching process, a higher roughness and higher mean distance between nearest-neighbor pyramids with respect to substrate A. The results concerning the size of the obtained AuPd NPs by the laser irradiations with the laser fluence fixed shows that the substrate topography impacts on the dewetting process. In particular, we found that below a critical thickness of the deposited AuPd film, the NPs formed on substrates A and B have similar size and a similar trend for the evolution of their size versus the film thickness (i.e., the dewetting process is not influenced by the substrate topography since the film does not interact with the substrate topography). On the other hand, however, above a critical thickness of the deposited AuPd film, the AuPd NPs show a higher mean size (versus the film thickness) on substrate B than on substrate A, indicating that the AuPd film interacts with the substrate topography during the dewetting process. These results are quantified and discussed by the description of the substrate topography effect on the excess of chemical potential driving the dewetting process.

Influence of Fluorine-Doped Tin Oxide Coated on NiCrAl Alloy Foam Using Ultrasonic Spray Pyrolysis Deposition

Fluorine-doped tin oxide (FTO) coated NiCrAl alloy foam is fabricated using ultrasonic spray pyrolysis deposition (USPD). To confirm the influence of the FTO layer on the NiCrAl alloy foam, we investigated the structural, chemical, and morphological properties and chemical resistance by using USPD to adjust the FTO coating time (12, 18, and 24 min). As a result, when an FTO layer was coated for 24 min on NiCrAl alloy foam, it was found to have an enhanced chemical resistance compared to those of the other samples. This improvement in the chemical resistance of using USPD NiAlCr alloy foam can be the result of the existence of an FTO layer, which can act as a protection layer between the NiAlCr alloy foam and the electrolyte and also the result of the increased thickness of the FTO layer, which enhances the diffusion length of the metal ion.

Performance optimization of fluorine-doped tin oxide thin films by introducing ultrasonic vibration during laser annealing

Commercial fluorine-doped tin oxide (FTO) thin films were subjected to laser annealing coupled with ultrasonic vibration (48kHz and 350W). The effects of ultrasonic vibration, laser fluence and defocusing amount were systematically studied. Laser annealing could result in grain growth or damage of the FTO layer, and introducing ultrasonic vibration during laser annealing could effectively enhance the film compactness, decrease the film thickness and refine the grains in the film. As a result, the optical and electrical properties of the ultrasonic-vibration-assisted laser-annealed FTO films were significantly improved by using low laser fluences and high defocusing amounts, and were slightly deteriorated when high laser fluences and low defocusing amounts were adopted. The results indicated that the film obtained by ultrasonic-vibration-assisted laser annealing using a laser fluence of 0.6J/cm2 and a defocusing amount of 2.0mm had the best overall photoelectric property with an average transmittance of 84.1%, a sheet resistance of 8.9Ω/sq and a figure of merit of 1.99×10–2Ω–1, outperforming that of the film obtained by pure laser annealing using the same experimental parameters. The present study confirms the efficacy of ultrasonic-vibration-assisted laser annealing in optimizing performance of FTO films.

Supercapacitive performances of MnO2 nanostructures grown on hierarchical Cu nano leaves via electrodeposition

This report describes the fabrication of hybrid electrode system made up of Fluorine-doped tin oxide (FTO), Copper nano leaves and MnO2 nanocrystals in a layer by layer hierarchy. FTO layer on glass was fabricated using a spray pyrolysis process, over that leaves like copper nanostructures were grown by bulk electrolysis method. MnO2 nanocrystals were further coated over FTO-Cu hybrid pattern using manganese acetate as the precursor through electrodeposition process. Purity, crystal structure analysis, structural morphology of all the layers were performed through XRD, FESEM with EDX, AFM etc. XRD pattern confirms the presence of pure FTO, Cu nanoparticles, and MnO2 nanostructures. FESEM micrographs reveal about the leaves like copper pattern, prism-like FTO and needle-shaped MnO2 particles in nano range. Cyclic voltammetry studies performed using electrochemical workstation exhibit a very high specific capacitance values of 486 & 376.7Fg−1 for the hybrid electrodes in which MnO2 coating time was set to about 350s and 250s respectively. Further, Electrochemical Impedance spectroscopic analysis (EIS) supports the pseudocapacitive nature of the fabricated hybrid electrode with a typical semi-circle like EIS curve in the lower frequency region.

An Electrochemical Method for Fast and Controlled Etching of Fluorine-Doped Tin Oxide Coated Glass Substrates

Fluorine-doped tin oxide (FTO) coated glass substrates are etched by a mixture of Zn and HCl for solar cells, flat panel displays, and related applications. However, this chemical etching method has its own limitations, and the most important limitation is no control on the etching process. Here, we report a controlled etching of FTO-coated glass substrate by a chronoamperometric method. In this method, optimized step potentials, −3 V for 10 s, −5 V for 80 s and −9 V for 10 s are applied between the FTO substrate to be etched and a counter electrode dipped in acidic 0.1 M FeCl3 (aq) electrolyte. The etched FTO was characterized by the energy dispersive X-ray spectroscopy showing complete removal of conducting FTO layer that was further studied by current-voltage characteristics. The chemical reaction involved in this etching process was investigated by the X-ray photoelectron spectroscopy that reveals similar chemical reaction as reported for the chemical method.

Cr-doped TiO2-based dye-sensitized solar cells with Cr-doped TiO2 blocking layer

Cr-doped TiO2 nanoparticles were synthesized by chemical sol–gel method. The anatase phase of TiO2 nanoparticles was proved by X-ray diffraction analysis. Furthermore, the field emission scanning electron microscopy revealed that the size of the nanoparticles was about 30 nm. TiO2 nanoparticles with 0.5 % Cr dopant concentration were selected to fabricate dye-sensitized solar cells due to their smaller band gap. Furthermore, Cr-doped TiO2 thin films (0.5 %) with different thicknesses were employed as blocking layer on the surface of fluorine-doped tin oxide (FTO) substrate. The current density–voltage measurement showed that the photovoltaic parameters of the fabricated dye-sensitized solar cells were improved after introducing Cr-doped TiO2 blocking layer at the interface of FTO and Cr-doped TiO2 mesoporous layer. The maximum power conversion efficiency increased more than 110 % as a result of inserting the Cr-doped blocking layer. The electrochemical impedance spectroscopy indicated that a more efficient charge transfer process takes place at the interface of the FTO/TiO2 due to the enhanced interfacial properties and reduction of charge recombination.

Efficient TiO2 blocking layer for TiO2 nanorod arrays-based dye-sensitized solar cells

Thin compact titanium dioxide (TiO2) blocking layer was chemically deposited on fluorine doped tin oxide (FTO) coated glass substrate using peroxo-titanium complex (PTC) solutions. After that, TiO2 nanorod (TNR) arrays of different thickness were grown on this TiO2 film by hydrothermal method. The blocking layer's crystal structure, morphology, and thickness were characterized using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy measurements. XPS analysis revealed that the TiO2 blocking layer derived from PTC maintains high degree of Ti–O–Ti linkage. These TiO2 materials were used as the photo-anode in the fabrication of dye-sensitized solar cells (DSSC). TNR arrays-based DSSC of thickness 6.2μm with TiO2 blocking layer showed higher photo-electric conversion efficiency of 1.46% compared to devices with similar TNR array of thickness, 6.1μm without TiO2 blocking layer (1.19%). The reason can be ascertained from dark photocurrent density–voltage measurements of the devices which reveal that the TiO2 blocking layer diminishes the dark current arising from reduction of I3− at the FTO/electrolyte interface apparently by blocking direct contact of the redox electrolyte with the FTO layer.

Well-Defined Nanostructured, Single-Crystalline TiO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells.

An electron transporting layer (ETL) plays an important role in extracting electrons from a perovskite layer and blocking recombination between electrons in the fluorine-doped tin oxide (FTO) and holes in the perovskite layers, especially in planar perovskite solar cells. Dense TiO2 ETLs prepared by a solution-processed spin-coating method (S-TiO2) are mainly used in devices due to their ease of fabrication. Herein, we found that fatal morphological defects at the S-TiO2 interface due to a rough FTO surface, including an irregular film thickness, discontinuous areas, and poor physical contact between the S-TiO2 and the FTO layers, were inevitable and lowered the charge transport properties through the planar perovskite solar cells. The effects of the morphological defects were mitigated in this work using a TiO2 ETL produced from sputtering and anodization. This method produced a well-defined nanostructured TiO2 ETL with an excellent transmittance, single-crystalline properties, a uniform film thickness, a large effective area, and defect-free physical contact with a rough substrate that provided outstanding electron extraction and hole blocking in a planar perovskite solar cell. In planar perovskite devices, anodized TiO2 ETL (A-TiO2) increased the power conversion efficiency by 22% (from 12.5 to 15.2%), and the stabilized maximum power output efficiency increased by 44% (from 8.9 to 12.8%) compared with S-TiO2. This work highlights the importance of the ETL geometry for maximizing device performance and provides insights into achieving ideal ETL morphologies that remedy the drawbacks observed in conventional spin-coated ETLs.

Copper oxide hole transport materials for heterojunction solar cell applications

In this study, polymer:fullerene bulk-heterojunction hybrid solar cells with the structure, fluorine-doped tin oxide (FTO)/Cu2O/poly (3-hexylthiophene): 6,6-phenyl-C61-butyric acid methyl ester (P3HT:PCBM):TiO2/Ca/Al, were fabricated. The effect of a p-type Cu2O thin layer deposited between the active layer (P3HT:PCBM) and the FTO layer on cell performance was investigated; the p-type Cu2O thin layer was deposited through thermal evaporation. The results showed that the Cu2O interfacial layer increased the efficiency and stability of the hybrid solar cells. The optimal performance was obtained for the solar cell structure FTO/Cu2O (10nm)/P3HT:PCBM:TiO2 (15wt.%)/Ca/Al (best cell structure), which had the following specifications: open-circuit voltage=0.58V, short circuit current density=12.14mA/cm2, fill factor=58.63%, and η=4.13%. The Cu2O layer prevented the rapid degradation of the interface, thereby increasing the lifetime of the hybrid solar cells.

Effect of thermal treatment on solid–solid interface of hematite thin film synthesized by spin-coating deposition solution

This work describes hematite films prepared by a spin-coating deposition solution (SCDS) method that is a sol–gel method derived technique. Hematite films were prepared at two heat treatment temperatures (500°C and 800°C) and the influence of thermal treatment on the photoelectrochemical performance was studied. In addition, since the SCDS method allows an optimal control of stoichiometry and impurity incorporation, hematite films modified with Zn2+ and Sn4+ were also prepared. The 800°C-treated hematite films had a higher wettability and roughness that enabled them to have a better photocatalytic response in comparison with that of 500°C-treated hematite films. Moreover, modified hematite films demonstrated to have a performance slightly better than that of undoped hematite film as shown in linear sweep voltammetry and chronoamperometry results. Although an improvement in the performance of hematite films was achieved by annealing at higher temperatures and incorporating Zn2+ or Sn4+, the general photocatalytic response of the films was poor. Two plausible hypotheses were discussed related to the (i) dopant segregation at grain boundary, and (ii) poor contact between the hematite and fluorine doped tin oxide layer (from the glass substrate), which was experimentally confirmed by a cross-sectional analysis conducted using scanning electron microscopy (SEM). In fact, additional experiments need to be done in order to improve the hematite deposition and make the SCDS a promise method for industrial application.

A study on linear and non-linear optical constants of Rhodamine B thin film deposited on FTO glass

The aim of this research was to fabricate/deposit the good quality thin film of Rhodamine B dye on fluorine doped tin oxide glass substrate by the low cost spin coating technique and study their linear and nonlinear optical parameters. The thickness of the thin film was measured about 300nm with alpha step system. The transmittance of the fabricated thin film was found to be above 75% corresponding to the fluorine doped tin oxide layer. The structural analysis was performed with X-rays diffraction spectroscopy. Atomic force microscope showed the topographic image of deposited thin film. Linear optical constant like absorption coefficient, band gap, and extinction index was calculated. The dielectric constant was calculated to know the optical response of Rhodamine B dye over fluorine doped tin oxide substrate. The nonlinear optical constant like linear optical susceptibility χ(1), nonlinear optical susceptibility χ(3), nonlinear refractive index (n2) were calculated by spectroscopic method. This method has advantage over the experimental method like Z-Scan for organic dye base semiconductors for future advance optoelectronics applications like dye synthesis solar cell.

Efficient planar perovskite solar cells without a high temperature processed titanium dioxide electron transport layer

Planar perovskite solar cells with a p–i–n structure use both hole-transport layers and electron-transport layers to promote collection of photogenerated holes and electrons for achieving high performance, wherein a high temperature processed compact and mesoporous titanium dioxide are usually required. We report here efficient perovskite solar cells grown directly on ultraviolet–ozone treated fluorine-doped tin oxide (FTO) substrates without using any electron-transport layers. The morphology, structure, optical–electrical properties of perovskite films deposited on FTO substrates with and without ultraviolet–ozone treatment and their corresponding devices׳ performance have been studied and compared. Ultraviolet–ozone treatment of FTO substrates improves the smoothness and coverage of CH3NH3PbI3−xClx films, which avoids direct contact between FTO and hole-transport layer. A planar electron-transport layer free device with a power conversion efficiency of over 10% has been achieved, suggesting that the widely adopted electron-transport layer is not a requirement for an efficient device.

APCVD of dual layer transparent conductive oxides for photovoltaic applications

We report the atmospheric pressure chemical vapour deposition (APCVD) of a dual layer transparent conductive oxide (TCO). This combines a fluorine doped tin oxide (FTO) base layer with a fluorine doped zinc oxide (FZO) top layer, where we seek to utilise the respective advantages of each material and the differences in their associated industrial deposition process technologies. Deposition of a 250nm thick FZO layer on FTO was enough to develop features seen with FZO only layers. The crystallographic orientation determined by the FZO dopant concentration. Changes to the deposition parameters of the underlying FTO layer effected stack roughness and carrier concentration, and hence optical scattering and absorption. Photovoltaic cells have been fabricated using this TCO structure showing promising performance, with efficiencies as high as 10.21% compared to reference FTO only values of 9.02%.The bulk of the coating was FTO, providing the majority of conductivity and the large surface features associated with this material, whilst keeping the overall cost low by utilising the very fast growth rates achievable. The FTO was capped with a thinner FZO layer to provide a top surface suitable for wet chemical or plasma etching, allowing the surface morphology to be tuned for specific applications.

Electrochemical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and carbon black composite as an electron injector into the electrolyte containing iodide redox couple

A composite of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer and carbon black powder (P/CB composite) is studied as an electron injector into the electrolyte of iodide redox couple in dye-sensitized solar cells (DSCs) replacing conventional platinum layer. P/CB composite films are coated with spin coating method on fluorine-doped tin oxide layer on glass substrate. The connectivity between carbon black powder is substantially improved with the addition of conducting PEDOT:PSS polymer which reduces the charge transport resistance through the composite layer. Post deposition thermal and acid treatments enhance the conductivity and connectivity. The charge transfer resistance at the electrolyte and P/CB composite electrode interface is also reduced because both PEDOT:PSS and carbon black act as a catalyst for the reduction of I3− into I−. The charge transfer resistance is increased, however, when the amount of PEDOT:PSS is higher than 20wt% because most of pores between carbon black powder are filled with PEDOT:PSS to reduce the interface area. The thickness of P/CB composite layer is optimized and an electrochemical circuit model is applied along with the electrochemical impedance measurement to explain the electrochemical behavior of this composite layer. A DSC made of 4.5μm thick P/CB composite layer with 17wt% PEDOT:PSS shows high performance (efficiency: 7.4%) which is comparable to Pt-based DSCs (efficiency: 7.7%). Furthermore, the P/CB composite can serve as a catalytic electrode on both bare glass and PET sheets, and DSCs with these FTO-free electrodes show high efficiencies >7.0%. Thus, the P/CB composite would open new prospects for realizing a printing process with flexible substrates at low temperature.

A comparative study of different M(M = Al, Ag, Cu)/FTO bilayer composite films irradiated with nanosecond pulsed laser

Aluminium (Al), silver (Ag) and copper (Cu) layers were deposited on commercial fluorine-doped tin oxide (FTO) glass by direct current (DC) magnetron sputtering, so as to form Al/FTO, Ag/FTO and Cu/FTO bilayer films. Then all the as-deposited metal/FTO films were irradiated using a 532nm nanosecond pulsed laser with a fluences of 1.05J/cm2. X-ray diffraction (XRD) analysis confirmed that all the laser-irradiated films were annealed by the laser and showed increased average crystallite size in FTO layers. Laser-induced grating structures were also obtained on the surfaces of the laser-irradiated Ag/FTO and Cu/FTO films, resulting in higher surface roughnesses and average transmittances of the films. But due to the broken continuity of the Ag and Cu layers, the sheet resistances of these two films slightly decreased as compared to that of the laser-irradiated Al/FTO film. It was also found that the laser-irradiated Ag/FTO film, whose average transmittance in 400–800nm waveband and sheet resistance was 81.5% and 6.6Ω/sq respectively, had the better figure of merit, indicating that the photoelectric property of FTO-based bilayer films could be further optimized through achieving fabrication of laser-induced grating structures and laser annealing in one step.