Nanostructured Indium Tin Oxide Electrode Research Articles

Nanostructured front electrodes for perovskite/c-Si tandem photovoltaics.

The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by ∼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9 mA/cm2 absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to ∼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%.

Tuning the deposition parameters for optimizing the faradaic and non-faradaic electrochemical performance of nanowire array-shaped ITO electrodes prepared by electron beam evaporation.

Nanostructured indium tin oxide (ITO) surfaces present an interesting yet unusual combination of properties (high electrical conductivity and optical transparency) at a high surface-to-volume ratio. Thus, previous studies presented nanostructured ITO electrodes as potentially suitable platforms for electrochemical biosensors, but still there is a lack of research on the optimization of preparation methods for such electrodes. We present a systematic study on the properties of nanostructured ITO electrodes prepared by physical deposition, where the substrate temperature was tuned for achieving the best combination of structural properties (namely electrical conductivity and optical transparency) and electrochemical performance. Analysis of faradaic cyclic voltammetry (CV) was performed to determine the electroactive surface area of the samples, and these results were benchmarked against those obtained by non-faradaic CV and Mott-Schottky (MS) analysis. The latter was useful to determine the dependence of some intrinsic features of the semiconductor on the substrate temperature during deposition. The results show that, out of a wide temperature range covering from 200 °C to 500 °C, there is a two-phase temperature-dependent growth, explained by the Stranski-Krastanov and self-catalytic vapor-liquid-solid (VLS) methods, and, on the other hand, that there is an optimal growth temperature at 300 °C that maximizes the electroactive surface area and sensitivity. This means that cost-effective electrodes can be prepared at low temperatures outperforming in terms of electroactive surface area, surface capacitance and sensitivity. As a proof-of-concept, nanostructured ITO electrodes were electrochemically derivatized with aryl diazonium salts (as a first step towards biochemical functionalization), and the performance of the optimized electrodes was tested in a real scenario.

Novel nanostructured indium tin oxide electrode for electrochemical immunosensors: Suitability for the detection of TNF-α

The need for new and innovative point of care (POC) systems providing a feasible alternative to costly and time consuming standard laboratory techniques is becoming more evident every day, particularly in the case of cardiovascular diseases. Coupling optical and electrochemical principles for highly specific and sensitive detection of biomarkers could boost the successful implementation of POC systems in biomedical environments. We suggest indium tin oxide (ITO) as a promising material for working electrodes in optoelectrochemical sensors, owing to the rare combination of high electrical conductivity and optical transparency it presents. Moreover, the nanostructured nature of the electrodes' surface is crucial for an eventual miniaturization of the POC system. In this work, we describe the construction and characterization of a nanostructured ITO electrode modified with aryl diazonium salt as transparent substrate for electrochemical immunosensors. The developed electrode was tested for the detection of tumour necrosis factor α (TNF-α), a cardiac biomarker playing an important role in the prevention of heart failure. Macro and microscopic evidences (gathered from electrochemical and spectral techniques) of covalent bonding and high surface coverage are provided. Specific interaction between antigen (TNF-α) and monoclonal antibody (Ab-TNF-α) was verified by fluorescence patterning, confirming the proper bio-recognition of the cytokine. As a proof-of-concept, results of electrochemical impedance spectroscopy (EIS) show stabilized semi-quantitative label-free detection of TNF-α at several concentrations (from 10 pg/mL to 100 pg/mL). These preliminary results demonstrate the feasibility of using transparent substrates for the detection of cytokines at low concentrations, and the consequent application in POC systems for the monitoring of cardiovascular diseases.

Nanostructured indium tin oxide electrodes immobilized with toll-like receptor proteins for label-free electrochemical detection of pathogen markers

We describe the development of 3D nanostructured indium-tin oxide (ITO) electrodes, immobilized with toll-like receptor proteins (TLRs) for label-free detection of pathogen-associated molecular patterns (PAMPs). Nanostructured ITO electrodes were fabricated on ITO-coated glass substrates using the glancing angle deposition (GLAD) technique. Two different TLRs (TLR4 and TLR5), which recognize different PAMPs, were immobilized onto different GLAD ITO electrodes using a simple, robust and direct methodology with an epoxysilane as the intermediate layer. The immobilization steps were characterized using microscopy, electrochemical techniques and x-ray photoelectron spectroscopy. The changes to electron charge transfer resistance in electrochemical impedance spectroscopy (EIS) of the TLR-based sensors triggered by independent exposures of the TLR4-modified sensor to E. coli O157:H7 endotoxin (lipopolysaccharide, LPS) and the TLR5-modified sensor to flagellin from Salmonella typhimurium were examined. These sensors showed a wide dynamic range (>104) and two-orders of magnitude lower detection limits and 30 times better sensitivity for LPS and flagellin compared to planar gold and ITO-based TLR sensors. Unlike other sensors that exploit specific pathogen recognition elements, TLR-based EIS biosensors have the potential to carry out broad-spectrum detection and classification of pathogens in near-real time.

Understanding the Effects of a High Surface Area Nanostructured Indium Tin Oxide Electrode on Organic Solar Cell Performance.

Organic solar cells (OSCs) are a complex assembly of disparate materials, each with a precise function within the device. Typically, the electrodes are flat, and the device is fabricated through a layering approach of the interfacial layers and photoactive materials. This work explores the integration of high surface area transparent electrodes to investigate the possible role(s) a three-dimensional electrode could take within an OSC, with a BHJ composed of a donor-acceptor combination with a high degree of electron and hole mobility mismatch. Nanotree indium tin oxide (ITO) electrodes were prepared via glancing angle deposition, structures that were previously demonstrated to be single-crystalline. A thin layer of zinc oxide was deposited on the ITO nanotrees via atomic layer deposition, followed by a self-assembled monolayer of C60-based molecules that was bound to the zinc oxide surface through a carboxylic acid group. Infiltration of these functionalized ITO nanotrees with the photoactive layer, the bulk heterojunction comprising PC71BM and a high hole mobility low band gap polymer (PDPPTT-T-TT), led to families of devices that were analyzed for the effect of nanotree height. When the height was varied from 0 to 50, 75, 100, and 120 nm, statistically significant differences in device performance were noted with the maximum device efficiencies observed with a nanotree height of 75 nm. From analysis of these results, it was found that the intrinsic mobility mismatch between the donor and acceptor phases could be compensated for when the electron collection length was reduced relative to the hole collection length, resulting in more balanced charge extraction and reduced recombination, leading to improved efficiencies. However, as the ITO nanotrees increased in height and branching, the decrease in electron collection length was offset by an increase in hole collection length and potential deleterious electric field redistribution effects, resulting in decreased efficiency.

Solar biosupercapacitor

Here we report on an entirely new kind of bioelectronic device – a solar biosupercapacitor, which is built from a dual-feature photobioanode combined with a double-function enzymatic cathode. The self-charging biodevice, based on transparent nanostructured indium tin oxide electrodes modified with biological catalysts, i.e. thylakoid membranes and bilirubin oxidase, is able to capacitively store electricity produced by direct conversion of radiant energy into electric energy. When self-charged during 10min, using ambient light only, the biosupercapacitor provided a maximum of 6mWm−2 at 0.20V.

Nano-honeycomb structured transparent electrode for enhanced light extraction from organic light-emitting diodes

A universal nano-sphere lithography method has been developed to fabricate nano-structured transparent electrode, such as indium tin oxide (ITO), for light extraction from organic light-emitting diodes (OLEDs). Perforated SiO2 film made from a monolayer colloidal crystal of polystyrene spheres and tetraethyl orthosilicate sol-gel is used as a template. Ordered nano-honeycomb pits on the ITO electrode surface are obtained by chemical etching. The proposed method can be utilized to form large-area nano-structured ITO electrode. More than two folds' enhancement in both current efficiency and power efficiency has been achieved in a red phosphorescent OLED which was fabricated on the nano-structured ITO substrate.

Efficiency improvement in organic solar cells with nano-structured ITO electrodes

In this paper we use the finite difference time domain (FDTD) method to show that the efficiency of an organic photovoltaic cell can be significantly improved by nanostructuring the indium tin oxide (ITO) layer with 2D periodic arrays of holes. With air filling of the ITO structure, the number of absorbed photons is increased by 24.8% and the absorptance is increased by 22.1%. This paper also assesses the effect of allowing the adjacent poly(3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer to the fill the grating, in which case lower enhancements are found of 7.5% and 8.6% respectively. Finally, low-loss dielectric filling using poly(methyl methacrylate) (PMMA) is assessed, and enhancements of 15% and 16% are found.

Tuning the reactivity of nanostructured indium tin oxide electrodes toward chemisorption.

This contribution highlights correlation between the surface concentration of a chemisorbed organophosphorous probe (flavin mononucleotide) and the relative hydroxyl surface coverage of nanostructured ITO electrodes, which can be tuned during post-deposition reductive annealing. The resulting modified electrodes are very stable in aqueous solution, highly hydrophilic and fully-accessible to the bulk solution.

Texture design of electrodes for efficiency enhancement of organic solar cells

We report a simple solution-based approach to form ordered patterns of an indium tin oxide (ITO) electrode and underlying reasons for the improvement in power conversion efficiency (PCE) of organic solar cells (OSCs) built on the nanostructured ITO electrode. The patterning of ITO was achieved by using nanospheres as the template to erode ITO by wet chemical etching. Using a textured ITO anode for poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM) (P3HT:PCBM) OSCs enhanced PCE by 15% with respect to the non-patterned ITO anode. The improvement is mostly attributed to the morphological and interfacial changes stemming from the textured ITO electrode as well as enhanced light absorption due to the optimal morphology and refractive index change of patterned ITO. With its simplicity and time-saving, this method of fabricating a unique pattern of ITO electrodes can be widely applicable to a variety of large-area thin film solar cells.

Fabrication of Dye-Sensitized Solar Cells with a 3D Nanostructured Electrode

A novel Dye-Sensitized Solar Cell (DSSC) scheme for better solar conversion efficiency is proposed. The distinctive characteristic of this novel scheme is that the conventional thin film electrode is replaced by a 3D nanostructured indium tin oxide (ITO) electrode, which was fabricated using RF magnetron sputtering with an anodic aluminum oxide (AAO) template. The template was prepared by immersing the barrier-layer side of an AAO film into a 30 wt% phosphoric acid solution to produce a contrasting surface. RF magnetron sputtering was then used to deposit a 3D nanostructured ITO thin film on the template. The crystallinity and conductivity of the 3D ITO films were further enhanced by annealing. Titanium dioxide nanoparticles were electrophoretically deposited on the 3D ITO film after which the proposed DSSC was formed by filling vacant spaces in the 3D nanostructured ITO electrode with dye. The measured solar conversion efficiency of the device was 0.125%. It presents a 5-fold improvement over that of conventional spin-coatedTiO2film electrode DSSCs.

Gold nanoparticle arrays directly grown on nanostructured indium tin oxide electrodes: Characterization and electroanalytical application

This work describes an improved seed-mediated growth approach for the direct attachment and growth of mono-dispersed gold nanoparticles on nanostructured indium tin oxide (ITO) surfaces. It was demonstrated that, when the seeding procedure of our previously reported seed-mediated growth process on an ITO surface was modified, the density of gold nanospheres directly grown on the surface could be highly improved, while the emergence of nanorods was restrained. By field emission scanning electron microscopy (FE-SEM) and cyclic voltammetry, the growth of gold nanoparticles with increasing growth time on the defect sites of nanostructured ITO surface was monitored. Using a [Fe(CN) 6] 3−/[Fe(CN) 6] 4− redox probe, the increasingly facile heterogeneous electron transfer kinetics resulting from the deposition and growth of gold nanoparticle arrays was observed. The as-prepared gold nanoparticle arrays exhibited high catalytic activity toward the electrooxidation of nitric oxide, which could provide electroanalytical application for nitric oxide sensing.