Bare Fluorine-doped Tin Oxide Research Articles

Ultrasensitive electrochemical sensors based on Cu and Cu@Ag nanorods for simultaneous heavy metal detection

This work reports the development of ultrasensitive miniaturized electrochemical device for heavy metal sensing. A laser engraver based patterning of fluorine-doped tin oxide (FTO) sheet was done to draw an etched pattern forming a miniaturized 3-electrode configuration. A layer of Ag/AgCl ink served as pseudo-reference electrode. The sensing electrode was coated using low-cost Cu nanorods (CuNRs) grown radially along the {110} surface with aspect ratio of 8.0 and Cu@Ag core-shell nanorods (Cu@AgNRs) formed via galvanic displacement for simultaneous electrocatalytic detection of heavy metal ions (Pb(II), Cd(II), Hg(II), and Zn(II)) present in water. The electroactive surface area of the prepared devices is 0.026, 0.093 and 0.125 cm2 for bare FTO, CuNRs/FTO and Cu@AgNRs/FTO, respectively. Bimetal Cu@AgNRs/FTO sensor exhibited the lowest limit of detection of 1, 2, 5 and 6 nM, respectively, detecting Cd(II), Pb(II), Zn(II), and Hg(II) ions, and it was 2, 2, 3 and 4 nM, respectively, for simultaneous detection of Zn(II), Pb(II), Cd(II) and Hg(II). The Cu@AgNRs/FTO based device showed distinct peak-to-peak separation by 0.40, 0.25 and 0.51 V for Zn(II)-Cd(II), Cd(II)-Pb(II) and Pb(II)-Hg(II), respectively. This device was highly sensitive (583.6–1261.8 μA․μM−1․cm−2) for heavy metal detection over CuNRs/FTO (15.9–107.4 μA․μM−1․cm−2). The Cu@AgNRs/FTO based sensors demonstrated good reproducibility (relative standard deviation ≤ 5%) with recovery (>90%) in the case of all target heavy metals simultaneously present in environmental water samples. Hence, the Cu nanorods based miniaturized sensing platforms developed in the present study for simultaneous heavy metal detection are potential low-cost alternatives providing a repeatability of upto 4 cycles unlike the commercial screen-printed electrodes.

Interfacial carbon quantum dot thin film impacts on morphological and chemical structures of fluorine-doped tin oxide films

Morphology and chemical bonding states, including surface roughness, film density, F-doping, and oxygen vacancy (VO) concentration directly affect the electrical and optical properties of fluorine-doped tin oxide (FTO) films. In this study, morphology and chemical bonding states of FTO films are engineered simultaneously by introducing a carbon quantum dot (CQD) thin film as an interface layer during ultrasonic spray pyrolysis deposition. The abundant oxygen-containing surface functional groups and large surface free energy of the CQD thin film promoted (200) oriented crystal growth and accelerated nucleation of FTO, resulting in smooth and dense FTO film morphology. The abundant carboxyl surface functional groups on the CQDs generate active F− species that are effectively doped into SnO2. Formic acid, formed by dissociation of the carboxyl group, can serve as a strong reducing agent for extracting oxygen atoms from the SnO2 lattice, thereby increasing the VO concentration. The accelerated F-doping and VO concentration result in the generation of additional free electrons. The effects of the optimized CQD on the morphological and chemical structures of FTO films are demonstrated by their superior electrical (sheet resistance of ∼5.7 Ω/□) and optical properties (visible transmittance of ∼85.9 %) compared with bare FTO. Moreover, CQD/FTO used as transparent conducting electrodes in electrochromic (EC) application exhibited improved EC performances, including fast switching speeds (5.3 s and 2.3 s for bleaching and coloration, respectively) and high coloration efficiency (81.1 cm2/C) compared to that of bare FTO.

Cerium Ion Adsorption to Fluorine-Doped Tin Oxide Electrodes

The f-elements are critical in many technologies including electronics, catalysis, magnetics, and clean energy. Additionally, these elements occur in very low abundance worldwide. Research has therefore been motivated in the detection, quantification, and reclamation of these elements from waste streams. In this presentation we explore the use of fluorine-doped tin oxide (FTO) electrodes as sensitive and cost-effective electrochemical sensors for cerium ions. We demonstrate that cerium adsorbs reversibly to bare FTO surfaces with a dependence on pH. Through voltammetry and XPS characterization, we demonstrate that the adsorbed cerium, which can undergo the quasi-reversible CeIV/CeIII redox transition, exists in more than one chemical environment. Based on these data, we posit that these different environments are due to the buildup of multiple layers of cerium ions on the FTO surfaces. At lower concentrations (< ca. 100 uM), we can use voltammetry to quantify the cerium adsorbed to the FTO and relate it to the concentration of cerium in solution, with a lower detection limit of about 10-6 M. The data fits to a pseudo second order rate law with a rate constant on the order of 107 (cm2 mol-1)2 s-1. The adsorption fits well to the Freundlich model, but we are working towards finding a non-empirical adsorption model than provide the equilibrium constant for the adsorption reaction.

Enhanced nonlinear optical response by strong coupling between plasmonic antenna arrays and epsilon-near-zero film

A coupled structure of center-symmetric orthogonal nano-antenna arrays on fluorine-doped tin oxide (FTO) is designed to enhance the nonlinear response by the strong coupling. Further, we study the roles of structural and material parameters in determining the linear and nonlinear optical response of antenna-FTO metasurface. This structure shows broadband spectrum (∼900 nm) and large nonlinearity with nonlinear refractive index n 2 of 1.02 cm2/GW, which is about 400 times higher than that of bare FTO film. The results provide a promising platform for the realization of ultracompact and large nonlinear optical devices.

High-performance amperometric detection of hydroxylamine on fluorine doped tin oxide electrode modified with NiCo2O4 nanoparticles

The design and development of inexpensive, and extremely sensitive sensors for Hydroxylamine (HYA) are imperative due to its toxicity to animals, plants, and aquatic life. This work proposes a high-performance enzyme-free electrochemical sensor for HYA based on its oxidation on Nickel cobaltite (NCO) spinel-modified fluorine doped tin oxide (FTO) electrode. Hydrothermally grown irregularly shaped NCO nanoparticles (NPs) of size around 10 nm are characterized by XRD, XPS, UV–visible, BET, and TEM to evaluate the structural and morphological characteristics. NCO-modified FTO (NCO@FTO) electro-oxidizes HYA at a potential of 0.66 V vs. Ag/AgCl, delivering 1.7 times the current response than bare FTO. The rich catalytically active redox couples of Ni and Co, high conductivity, and high surface area of the NCO NPs contribute to the superior electrochemical response of NCO@FTO. As an amperometric sensor, NCO@FTO detects HYA in a wide range of 10 to 4000 µM concentration with a high sensitivity of 408 μA mM−1 cm−2. The sensor has a detection limit of 0.47 μM (S/N = 3), faster response of less than 3 s, excellent selectivity, and good stability. The practical feasibility of the proposed sensor is investigated by employing it in the monitoring of real samples. This study demonstrates NCO@FTO as an efficient low-cost sensor for HYA and extends the use of spinel metal oxides in bioanalysis.

A novel label-free graphene oxide nano-wall surface decorated with gold nano-flower biosensor for electrochemical detection of brucellosis antibodies in human serum

Conventional serological methods to detect brucellosis are time-consuming, expensive, and require special equipment, but they are less sensitive than newly developed approaches. To overcome these drawbacks, in addition to the ultrasensitive, rapid, easy, and early detection of brucellosis biomarkers, more emphasis on novel methods through electrochemical nanostructured platforms is needed. A novel nanostructured platform made of graphene oxide (GO) nanosheet and gold nanoparticles (AuNPs), with field emission scanning electron microscopy (FESEM) scanning revealing that the GO is vertically arranged on the surface like nano-walls (GONW) and the AuNPs are decorated in the shape of nanoflowers. FESEM, energy dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) were used to characterize the successfully fabricated nanostructured surface. The electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV) techniques applied to the fabricated graphene oxide nanowall-gold nanoflower (GONW@Au-NF) platform indicated excellent electroactivity (more than a 40% increase) and valuable antifouling properties, which make it more sensitive than bare fluorine-doped tin oxide (FTO) electrodes. The limit of detection (LOD) using different concentrations of Brucella–against antibody (Br-Ab) is estimated at 9.3 fg mL−1. The selectivity of the biosensor was tested using E.coli antibody and bovine serum albumin (BSA). The results revealed good selectivity (significant difference) and acceptable reproducibility (not exceeding 12% RSD). Rapid and early detection of Br-Ab in both PBS and real samples (serum), with excellent sensitivity and selectivity, proposed our fabricated biosensor as an ideal candidate for brucellosis biomarker detection.

11.4% Efficiency Kesterite Solar Cells on Transparent Electrode

AbstractThin film solar cells on semitransparent substrates are attracting much attention due to new application scenarios including building‐integrated photovoltaics (BIPV). Environmentally‐benign element constituted and highly stable kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells are ideal candidates for such applications. However, the efficiency of kesterite solar cells on semitransparent substrates is far behind that on opaque Mo‐based substrates. Here, fabrication of CZTSSe solar cells on fluorine‐doped tin oxide (FTO) substrates from molecular solution and how step‐by‐step absorber engineering improves device performance is reported. A power conversion efficiency of 7.02% is obtained when the absorber is fabricated on bare FTO, which is improved to 9.56% after adding a MoO3 interfacial layer. Investigations show the enhancement originates from the transformation of MoO3 to MoSe2 during film selenization which initiates crystallization at the back contact and at the same time prevents oversize grains at the absorber surface. Na‐doping and Ag alloying further facilitate grain growth and mitigate band tailing, resulting in a certified effective area efficiency of 11.43% with all device parameters comparable to that on an Mo‐substrate. This is the first time highly efficient kesterite solar cells are demonstrated on transparent electrodes, which opens up new opportunities for these earth‐abundant elements composed of thin film photovoltaics.

Efficient catalytic-activity-driven extremely low-voltage operatable multicolor electrochemiluminescence displays using Pt nanoparticles anchored on CuO nanorod electrodes

Electrochemiluminescence (ECL) displays have attracted significant attention because of their economic and processing advantages. However, despite these advantages, low luminous efficiency presents difficulties in their commercialization. To overcome this issue, a catalytic-activity-driven approach using Pt nanoparticles (NPs) anchored on CuO nanorod (NR) electrodes (PCNEs) is introduced. The Pt NPs facilitated the electron-transfer processes in the ECL reaction, and their catalytic activity was maximized by employing CuO NRs as nano-supports, offering more catalytic sites for Pt NPs. The optimized PCNE-based ECL display enabled extremely low-voltage operation of multicolor ECL displays, along with enhanced luminance compared with bare fluorine-doped tin oxide (FTO)-based ECL displays. ECL displays utilizing optimized PCNEs provide an effective template for next-generation ECL-material-based display applications.

Development of novel electrochemical sensor based on PtNPs-SeNPs-FTO nanocomposites via electrochemical deposition for detection of hydrogen peroxide

The PtNPs-SeNPs-FTO nanocomposites as electrochemical sensor was developed via electrochemical deposition method for hydrogen peroxide detection. The synthesis and growth of selenium nanoparticles (SeNPs), platinum nanoparticles (PtNPs) and nanocomposites of PtNPs-SeNPs on fluorine doped tin oxide (FTO) substrate by using electrochemical deposition for H2O2 detection was reported. Morphological and structural study of bare FTO, PtNPs-FTO, SeNPs-FTO and PtNPs-SeNPs-FTO sensor was confirmed by FEGSEM, EDS mapping, and XPS. Morphology of synthesized PtNPs and SeNPs decorated on the FTO surface showed nano-flower structure and spherical in shape respectively. The XPS analysis was carried out to identify elemental composition on the surface-modified PtNPs-SeNPs-FTO sensor. The survey spectra of PtNPs-SeNPs-FTO electrode displayed a considerable strong peak of C, F, Sn, O, Pt, and Se, which confirmed the existence of these elements on the FTO surface. The synthesized SeNPs-FTO, PtNPs-FTO, and PtNPs-SeNPs-FTO sensor displayed wide range of linear concentration response from 0.01 to 40 mM and response time 0.5 s. The synthesized SeNPs-FTO, PtNPs-FTO and PtNPs-SeNPs-FTO sensor showed sensitivity of 0.4 µA mM−1 cm−2 (R2 =0.9904), 17.2 µA mM−1 cm−2 (R2 =0.9917) and 7.3 µA mM−1 cm−2 (R2 = 0.9835) respectively. The SeNPs-FTO, PtNPs-FTO and PtNPs-SeNPs-FTO based sensor also demonstrated high selectivity towards detection of H2O2 with interfering agents.

Multistep Functional Embellishment for p-ZnTe as a Cathode to Boost the Faraday Efficiency of Nitrogen Conversion.

An electrochemical N2 reduction reaction (N2RR) is a selective sustainable approach to obtain NH3 at mild conditions and has been proposed as an alternative to the full-blown Haber-Bosch process. However, achieving high yields of NH3 and high faraday efficiency (FE) at a low overpotential remains a big challenge but has high expectations for the electrocatalytic N2RR. Herein, a novel p-ZnTe cathode multistep embellished with NiOx and ZnO thin films was prepared for boosting faraday efficiency to 9.89% for N2RR at -0.2 V vs reversible hydrogen electrode (RHE), about 12 times of p-ZnTe@ZnO. All components within the NiOx@p-ZnTe/ZnO electrode work cooperatively. A N source was determined through a 15N isotopic-labeling experiment. Using steady-state photoluminescence, electrochemical impedance spectroscopy, and control experiments, a possible model of charge transformation is built. In particular, a NiOx layer has an important impact on increasing interfacial contact between a bare fluorine-doped tin oxide (FTO) glass and p-ZnTe and further reinforcing interfacial electron transfer. This work provides a practical application and a feasible strategy to develop highly efficient catalysts for N2 reduction and also affords a guideline for the fabrication of a flat electrode.

Vertically oriented mesoporous silica film modified fluorine-doped tin oxide electrode for enhanced electrochemiluminescence detection of lidocaine in serum.

Owing to a nanochannel-based enrichment effect and anti-fouling ability, highly ordered and vertically oriented mesoporous silica thin film (VMSF) modified electrodes have demonstrated their great potential in direct and highly sensitive analysis of complex samples. In this work, a VMSF modified fluorine-doped tin oxide (FTO) electrode (VMSF/FTO) is fabricated for enhanced electrochemiluminescence (ECL) analysis of lidocaine in serum. VMSF with good integrity and mechanical stability can be rapidly and conveniently grown on FTO in a few seconds at room temperature using an electrochemically assisted self-assembly (EASA) method. Due to the strong electrostatic attraction between the cationic ECL probe and negatively charged nanochannel, the VMSF/FTO electrode shows significant enrichment of tris(2,2-bipyridine) ruthenium(ii) (Ru(bpy)32+), leading to ∼10 times enhancement of its ECL signal in comparison to the bare FTO electrode. Lidocaine, an anesthetic and antiarrhythmic drug, can act as the co-reactant of Ru(bpy)32+ and promote its ECL signal. Sensitive ECL detection of lidocaine is achieved by the sensor in a wide linear range from 10 nM to 50 μM with a low limit-of-detection (LOD) of 8 nM. Combined with the antifouling ability of VMSF, the VMSF/FTO electrode also realizes the accurate and rapid analysis of lidocaine in real serum samples.

Enhancement of photoelectrochemical properties with α–Fe2O3 on surface modified FTO substrates

Despite a number of favorable properties, several drawbacks need to be addressed before hematite can be considered a highly desirable material for applications in water-splitting photoelectrochemical (PEC) electrodes. In the present work, the PEC performance was improved by the synergetic effects of the preparation techniques and modification of the fluorine-doped tin oxide (FTO) glass. The hematite photoanodes deposited onto the pretreated FTO supports clearly decreased the overpotential by up to 100 mV with a higher photocurrent compared to the bare FTO glass. In particular, an electrochemical preparation method including moderate annealing resulted in a highly enhanced PEC performance by influencing the FTO glass during the electrode preparation process.

RbF modified FTO electrode enable energy-level matching for efficient electron transport layer-free perovskite solar cells

The development of highly efficient electron transport layer free perovskite solar cells (ETL-free PSCs) with simplified and economical device configurations can significantly motivate the commercialization of PSCs. However, the performance of ETL-free PSCs has been hampered by the sluggish charge extraction and severe charge carrier recombination due to the energy-level mismatch at the interface of the perovskite and the transparent conductive electrode FTO (fluorine doped tin-oxide). In this study, this issue is well solved by modifying the FTO surface with a simple, low-cost and non-toxic rubidium fluoride (RbF) interlayer. An interfacial dipole layer is formed on the FTO surface by inserting a RbF layer, which tunes the work function of FTO, eliminates the electron transport barrier and optimizes the energy-level alignment at the FTO/perovskite interface, thereby enhancing the charge transfer and suppressing the carrier recombination. Consequently, the rigid ETL-free PSCs with RbF layer yield high efficiencies of up to 18.79%, higher than that of ETL-free devices on bare FTO (16.03%). By virtue of the low-temperature processability, a superior PCE of 15.7% has been achieved by flexible ETL-free PSCs fabricated on RbF modified plastic substrate. This study provides a simple, efficient and environmentally friendly approach to modify the FTO electrode for fabricating ETL-free PSCs, which contribute to promote the design of advanced interface materials for simplified and high-performance perovskite photovoltaics.

Voltammetric behaviour of cationic redox probes at mesoporous silica film electrodes

The effect of vertically aligned silica nanochannels on the electrochemical response of various cationic redox probes has been investigated. To this end, an oriented mesoporous silica thin film has been generated by electro-assisted self-assembly onto a fluorine-doped tin oxide (FTO) electrode, which was then used to characterize the voltammetric behaviour of redox cations of different nature, size and charge. Methylene Blue (MB+), paraquat (PQ2+), diquat (DQ2+), ruthenium trisbipyridine (Ru(bpy)32+) and ruthenium hexamine (Ru(NH3)63+) were selected for that purpose. Multisweep cyclic voltammetry experiments showed significant accumulation of these cations thanks to favourable electrostatic interactions with the negatively-charge silica surface, but the enhancement of the votammetric signals compared to the bare FTO electrode was strongly dependent on the probe type, according the following trend: MB+ > PQ2+ > DQ2+ > Ru(bpy)32+ > Ru(NH3)63+. The accumulation processes were very fast owing to the vertical orientation of the mesopore channels ensuring fast diffusion from the solution to the electrode surface. Operating at various potential scan rates and different probe concentrations enabled to quantify the relative ratio between surface-confined and diffusion-controlled processes, the adsorption phenomena being clearly more prominent in diluted media and also accentuated at high potential scan rates. The mesoporous silica film electrodes exhibited higher sensitivities at lower concentrations, which can give benefits for sensor applications at trace levels.

Synthesis of aniline copolymer and as an active catalyst layer for electrochemical reduction of carbon dioxide in water free of supporting electrolytes

• Synthesis of poly(aniline-co- 2- amino -4- hydroxybenzenesulfonic acid) (PAAHB). • PAAHB shows a little pH dependence for electrochemical redox and visible spectra. • PAAHB can catalyze the electroreduction of CO 2 in water free of supporting electrolytes. • PAAHB plays an important role in enhancing charge transfer rate. • PAAHB has the high product selectivity toward electroreduction of CO 2 . Aniline copolymer, poly(aniline- co -2-amino-4-hydroxybenzenesulfonic acid) (PAAHB), is electrodeposited on a fluorine doped tin oxide (FTO) glass, which can effectively catalyze the electrochemical reduction of carbon dioxide in water free of supporting electrolyte. In fact, this solution is a self-electrolyte one due to the presence of H + and HCO 3 − ions in CO 2 -saturated water. The catalytic ability of PAAHB towards CO 2 electroreduction is 37.7 times as high as that of a bare FTO glass at 20 mV s -1 based on the cyclic voltammograms, and is also 35.4 times as high as that of the bare FTO electrode in 0.1 M NaHCO 3 solution at 60 mV s -1 , which would be attributed to free radicals in the copolymer. Furthermore, a sandwich electrode, PAAHB/n-FTO/PAAHB/FTO glass, shows even higher catalytic activity that is 60.1 times as high as that of the bare FTO electrode at 20 mV s -1 , and is 64.4 times as high as that of the bare FTO electrode in 0.1 M NaHCO 3 solution at 60 mV s -1 . A key problem is the low solution conductivity, which fortunately is compensated by the faster charge transfer and the high catalytic activity of PAAHB. The product solution obtained is analyzed using 1 H NMR and gas chromatography. The product is only methanol, indicating that PAAHB has high selectivity towards CO 2 electroreduction. Faradaic efficiency of methanol is approximately 66.4%.

Interface engineering of C60/ fluorine doped tin oxide on the photovoltaic performance of perovskite solar cells using the physical vapor deposition technique

Fullerene (C60) has been demonstrated, using vapor deposition, to be a good electron transport layer (ETL) and different thicknesses have been utilized in n-i-p configuration perovskite solar cells. However, an underlying reason for the variation in thicknesses, which hinders the reproducibility of perovskite solar cells employing a C60 ETL, has not been well-examined. This study reveals that the surface roughness of the conducting glass, such as fluorine doped tin oxide (FTO), affects the photovoltaic performance while optimizing the thickness of the vacuum deposited compact C60 ETL. A low-thickness C60 ETL retains a surface roughness and Ohmic behavior similar to bare FTO due to physical defects at the C60/FTO interface. Increasing the thickness further reduces the defects at the C60/FTO interface and facilitates an enhanced electron extraction from a vacuum co-deposited methyl-ammonium lead iodide perovskite light absorber. As a result, a perovskite solar cell with a homogenously covered C60 ETL on an FTO substrate delivers a power conversion efficiency of 14.63%. These comprehensive characterizations support the finding that suppression of defects at the C60/FTO interface results in an improved photovoltaic performance. This work demonstrates that the surface roughness of FTO needs to be considered for a decisive compact ETL for enhanced photovoltaic performance and reproducibility.

Modification of fluorine-doped tin oxide surface: Optimization of the electrochemical grafting of diazonium salt

Fluorine-doped tin oxide (FTO) electrodes were functionalized by electro reduction of in situ generated 4-carboxyphenyl diazonium salt. Several grafting potentials and times were investigated in order to find the optimal grafting conditions. The electrochemical behavior of bare FTO electrodes in the presence of the diazonium, together with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) characterization of the grafted electrodes in the presence of redox probes ferricyanide and ferrocene allowed us to conclude that 10 min grafting under a controlled potential of −0.50 V lead to the formation of a poorly-packed organic multi-layer on the electrode surface. X-ray Photoelectron Spectroscopy (XPS), together with Fourier-Transform Infrared Spectroscopy (FTIR) analyses, further evidenced the presence of carboxylic groups onto modified FTO electrodes.

Electrodeposition and Characterization of a Tin Sulfide‐Electrochemically Reduced Graphene Oxide Heterojunction

AbstractThis work shows the formation of a heterojunction between tin (II) sulfide (SnS) and electrochemically reduced graphene oxide (ERGO), carried out through two electrochemical steps. In the first step, graphene oxide (GO) was electrochemically reduced on a fluorine‐doped tin oxide (FTO) electrode. In the second step, the ERGO/FTO substrate was used as an electrode for the electrodeposition of SnS. In this study, each electrodeposited material (ERGO, SnS and SnS/ERGO heterojunction) was analyzed and characterized using different techniques, which confirmed the SnS/ERGO heterojunction formation. By employing electrochemical impedance spectroscopy (EIS) and linear sweep photovoltammetry measurements, it was confirmed that SnS deposited in both, bare FTO and ERGO, is a p‐type semiconductor. Furthermore, an improvement of the photocatalytic properties of the SnS/ERGO photocathode in comparison with the SnS film was observed. This effect is related to the ERGO interlayer between the SnS film and the FTO electrode, and the structural and morphology modification of the SnS film onto ERGO.

Blocking the Charge Recombination with Diiodide Radicals by TiO2 Compact Layer in Dye-Sensitized Solar Cells

The addition of a compact titanium dioxide (TiO2) layer between the fluorine-doped tin oxide (FTO) coated glass substrate and the mesoporous TiO2 layer in the dye-sensitized solar cell (DSC) based on the iodide/triiodide redox couple (I−/I3−) is known to improve its current-voltage characteristics. The compact layer decreases the recombination of electrons extracted through the FTO layer with I3− around the maximum power point. Furthermore, the short-circuit photocurrent was improved, which previously has been attributed to the improved light transmittance and/or better contact between TiO2 and FTO. Here, we demonstrate that the compact TiO2 layer has another beneficial effect: it blocks the reaction between charge carriers in the FTO and photogenerated diiodide radical species (I2−•). Using photomodulated voltammetry, it is demonstrated that the cathodic photocurrent found at bare FTO electrodes is blocked by the addition of a compact TiO2 layer, while the anodic photocurrent due to reaction with I2−• is maintained.

A new breakthrough for graphene/carbon nanotubes as counter electrodes of dye-sensitized solar cells with up to a 10.69% power conversion efficiency

A three-dimensional graphene/single-walled carbon nanotube counter electrode is developed for dye-sensitized solar cells via a drop-coating method. The resulting graphene/single-walled carbon nanotube counter electrode show satisfactory transmittance (56.6%) compared with that of bare fluorine-doped tin oxide glass (84.71%) at 670 nm. The obtained graphene/single-walled carbon nanotube counter electrode exhibits an excellent power conversion efficiency of 9.24%. When a mirror was set under the cells, the power conversion efficiency increased to 10.56%. Unexpectedly, in the stability test, its power conversion efficiency reached a maximum of 10.69%. This excellent performance was attributed to the three-dimensional structure, which had a large specific surface area. The cyclic voltammetry results indicate that the graphene/single-walled carbon nanotube had a higher catalytic I3− capability than that of Pt counter electrode, whereas the electrochemical impedance spectroscopy and Tafel test results prove that the graphene/single-walled carbon nanotube have a smaller resistance, which is consistent with the I-V characterization. We determine that the three-dimensional graphene/single-walled carbon nanotube counter electrode may have broad application prospects in dye-sensitized solar cells as a Pt-free material.