Self-organized Layers Research Articles

Bulk heterojunction solar cells made from carbazole copolymer and fullerene derivative with an inserted layer of discotic material with improved efficiency

ABSTRACTBulk heterojunction photovoltaic cells based on composites of copolymer poly [N-90-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] and the fullerene derivative [6,6]-phenyl C71-butyric acid methyl ester with an inserted layer of discotic liquid crystalline material (2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene) between the interface of active layer and hole transporting layer has been reported. Different hole transporting layers deposited on indium tin oxide substrates such as poly (3,4-ethylenedioxythiophene)-poly (styrenesulphonate) or molybdenum trioxide has been used in these devices. All the devices with inserted discotic liquid crystal layer showed better performance than the reference cells. Power conversion efficiency of 5.14% was achieved for these photovoltaic solar cells containing self-organised discotic liquid crystal layer of 30 nm thickness under one sun condition which is substantial jump as compared to earlier reports. The mobility of holes in the discotic liquid crystal inserted devices was found to be of the order of 10–6 cm2 V–1 s–1 due to which high values of current density was achieved. The influence of varying the thickness of liquid crystal layer and annealing on the photovoltaic parameters of these devices was also studied.

The use of artificial neural networks for classification of signal sources in cognitive radio systems

In the paper, methods of classification of signal sources in cognitive radio systems that are based on artificial neural networks are discussed. A novel method for improving noise immunity of RBF networks is suggested. It is based on introducing an additional self-organizing layer of neurons, which ensures automatic selection of variances of basis functions and a significant reduction of the network dimension. It is shown that the use of auto-associative networks in the problem of the classification of sources of signals makes it possible to minimize the feature space without significant deterioration of its separation properties.

Long-Term Stable Recombination Layer for Tandem Polymer Solar Cells Using Self-Doped Conducting Polymers.

PSS) as a p-type component of recombination layer (RL). However, its undesirable acidic nature, originating from insulating PSS, of PSS drastically reduces the lifetime of PSCs. Here, we demonstrate the efficient and stable tandem PSCs by introducing acid-free self-doped conducting polymer (SCP), combined with zinc oxide nanoparticles (ZnO NPs), as RL for PSS-free tandem PSCs. Moreover, we introduce an innovative and versatile nanocomposite system containing photoactive and p-type conjugated polyelectrolyte (p-CPE) into the tandem fabrication of an ideal self-organized recombination layer. In our new RL, highly conductive SCP facilitates charge transport and recombination process, and p-CPE helps to achieve nearly loss-free charge collection by increasing effective work function of indium tin oxide (ITO) and SCP. Because of the synergistic effect of extremely low electrical resistance, ohmic contact, and pH neutrality, tandem devices with our novel RL performed well, exhibiting a high power conversion efficiency of 10.2% and a prolonged lifetime. These findings provide a new insight for strategic design of RLs using SCPs to achieve efficient and stable tandem PSCs and enable us to review and extend the usefulness of SCPs in various electronics research fields.

A neural-network method for the synthesis of informative features for the classification of signal sources in cognitive radio systems

This paper discusses possible methods for the synthesis of informative features for the classification of signal sources in cognitive radio systems using artificial neural networks. A synthesis method based on the use of autoassociative neural networks is proposed. From the point of view of the classification of the signals, informativeness of synthesized features is estimated using a modified artificial neural network based on radial basis functions that contains an additional self-organizing layer of neurons that provide the automatic selection of the variance of basis functions and a significant reduction of the network dimension. It is shown that the use of autoassociative networks in the problem of the classification of signal sources makes it possible to synthesize the feature space with a minimum dimension while maintaining separation properties.

OH radical generation in a photocatalytic reactor using TiO2 nanotube plates

In order to use TiO2 nanotubes grown on a Ti plate as a photocatalyst, self-organized oxide nanotube layers were grown by anodization in a glycerol based electrolyte. The ultimate conditions for the synthesis of the TiO2 nanotube array on the Ti plate were investigated by comparing the morphology, length, and inner diameter of the nanotubes. They were significantly affected by the applied anodic voltage, anodization time, and composition of the electrolyte such as the water and fluoride ion concentration. The crystallographic structures of TiO2 nanotubes before and after annealing were compared. The photocatalytic reactor used in this study consisted of two parallel and closely spaced TiO2 nanotube plates. The plates were squares while a UV lamp was inserted perpendicularly to them. OH radical generation in the photocatalytic reactor was monitored by using a probe compound, parachlorobenzoate (pCBA). The steady state OH radical concentration was compared depending on the length of nanotubes and crystallographic structure. The longer the nanotubes, the higher the steady state OH radical concentration.

Roll to roll compatible fabrication of inverted organic solar cells with a self-organized charge selective cathode interfacial layer

A simple approach of fabricating efficient inverted devices with a self-organizing small-molecule electron extraction layerPhen-NaDPOby doctor-blading was demonstrated, which is compatible with roll to roll processing strategies.

Ferromagnetism of MnxSi1-x(x ∼ 0.5) films grown in the shadow geometry by pulsed laser deposition method

The results of a comprehensive study of magnetic, magneto-transport and structural properties of nonstoichiometric MnxSi1-x (x ≈ 0.51-0.52) films grown by the Pulsed Laser Deposition (PLD) technique onto Al2O3(0001) single crystal substrates at T = 340°C are present. A highlight of used PLD method is the non-conventional (“shadow”) geometry with Kr as a scattering gas during the sample growth. It is found that the films exhibit high-temperature (HT) ferromagnetism (FM) with the Curie temperature TC ∼ 370 K accompanied by positive sign anomalous Hall effect (AHE); they also reveal the polycrystalline structure with unusual distribution of grains in size and shape. It is established that HT FM order is originated from the bottom interfacial self-organizing nanocrystalline layer. The upper layer adopted columnar structure with the lateral grain size ≥50 nm, possesses low temperature (LT) type of FM order with Tc ≈ 46 K and contributes essentially to the magnetization at T ≤ 50 K. Under these conditions, AHE changes its sign from positive to negative at T ≤ 30K. We attribute observed properties to the synergy of distribution of MnxSi1-x crystallites in size and shape as well as peculiarities of defect-induced FM order in shadow geometry grown polycrystalline MnxSi1-x (x ∼ 0.5) films.

Universal energy level tailoring of self-organized hole extraction layers in organic solar cells and organic–inorganic hybrid perovskite solar cells

Tailoring the interface energetics between a polymeric hole extraction layer (HEL) and a photoactive layer (PAL) in organic photovoltaics (OPVs) and organic–inorganic hybrid perovskite solar cells (PrSCs) is very important to maximize open circuit voltage (Voc), power conversion efficiency (PCE), and device lifetime.

Development of the decision support subsystem in the systems of neural network pattern recognition by statistical information

The decision support subsystem in the neural network pattern recognition system, allowing to reduce the subjectivity and increase the quality of expert decisions in the construction of training samples by the statistical data of observations over the state of the management facilities of the production or social environment is developed. A functional structure of the NNPR system of the management facilities of the production or social environment by statistical information is proposed. According to the proposed structure, the problem-oriented NNPR system consists of subsystems of the initial data preparation for the PR and storage of the aggregated data, neural network models, and knowledge about the management facility of the production or social environment, as well as the support of the decision-making about its state. The decision support subsystem based on the proposed method of support of the classification decision-making using the Kohonen self-organizing layer is developed. The developed method of support of the classification decision-making provides a consistent implementation of the stages of self-organizing of neurons of the Kohonen computing layer, the calibration of the elements of the output vector of the training sample and their final labeling. An example of implementation of the proposed subsystem of support of decision-making about the class of the initialized labor protection project based on the expert estimates of the current level of the organization and working conditions at the enterprise is given. Using the developed decision support subsystem in the systems of NNPR by statistical information allows to adjust the decisions of the DM in accordance with the decisions of the neural network output machine, and thereby increase a relative share of correct expert estimates by 20 % on average and reduce false estimates for a number of pattern recognition problems by 50 %.

Evaluation of Corrosion Resistance of Nanotubular Oxide Layers on the Ti13Zr13Nb Alloy in Physiological Saline Solution / Ocena Odporności Korozyjnej Nanotubularnych Struktur Tlenkowych Na Stopie Ti13Zr13Nb W Środowisku Płynów Ustrojowych”

Evaluation of corrosion resistance of the self-organized nanotubular oxide layers on the Ti13Zr13Nb alloy, has been carried out in 0.9% NaCl solution at the temperature of 37ºC. Anodization process of the tested alloy was conducted in a solution of 1M (NH4)2SO4 with the addition of 1 wt.% NH4F. The self-organized nanotubular oxide layers were obtained at the voltage of 20 V for the anodization time of 120 min. Investigations of surface morphology by scanning transmission electron microscopy (STEM ) revealed that as a result of the anodization under proposed conditions, the single-walled nanotubes (SWNTs) can be formed of diameters that range from 10 to 32 nm. Corrosion resistance studies of the obtained nanotubular oxide layers and pure Ti13Zr13Nb alloy were carried out using open circuit potential, anodic polarization curves, and electrochemical impedance spectroscopy (EIS) methods. It was found that surface modification by electrochemical formation of the selforganized nanotubular oxide layers increases the corrosion resistance of the Ti13Zr13Nb alloy in comparison with pure alloy.

2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces.

We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems.

Open top anodic Ta3N5 nanotubes for higher solar water splitting efficiency

In the present work we grow self-organized Ta2O5 nanotube layers in a H2SO4/NH4F electrolyte at various elevated temperatures. Under optimized conditions we obtain 4μm long nanotubes that are well adherent to the substrate and can be grown very homogenous over large surface areas. Moreover, the key advantage of this approach is that an open top morphology (initiation layer free) is obtained. After a suitable conversion treatment in NH3 atmosphere Ta3N5 nanotubes are obtained, that after (Co-Pi+Co(OH)x) modification provide, under AM 1.5G illumination conditions, a photoelectrochemical current response of 4.7mAcm−2 at +1.23V vs RHE.

Improving the performance of organic solar cells using an electron transport layer of B4PyMPM self-assembled nanostructures

The electron transport (ETL) layer improves power conversion efficiency (PCE) in organic photovoltaic cells (OPVs) through the incorporation of the cathode interfacial layers. Here, we introduce [bis-4,6-(3,5-di-4-pyridylphenyl)-2-methylpyrimidine] (B4PyMPM) as an n-type buffer layer consisting of a self-organized layer with a horizontal configuration in bulk heterojunction OPVs. It is demonstrated that self-organization of this B4PyMPM compound in which molecules adopt a horizontal orientation parallel to the organic semiconducting substrate induces a large local interfacial electric field that results in a significant enhancement of exciton dissociation. The device using B4PyMPM as an ETL layers has a significantly high open circuit voltage (Voc = 0.64 V), good short circuit current (Jsc = 8.24 mA/cm2), good fill factor (FF = 0.65) and good PCE (3.42%). The physical properties of the device have also been studied from the measurements of impedance spectroscopy and photocurrent, which directly show the mechanisms occurring inside OPVs.

Enhanced Charge Transport in Tantalum Nitride Nanotube Photoanodes for Solar Water Splitting.

In the present work we grow anodic self-organized Ta2O5 nanotube layers, which are converted by ammonolysis to Ta3 N5 nanotubes, and then are used as photoanodes for photoanalytic water splitting. We introduce a two-step anodization process that not only improves order (reduced growth defects) and overall light absorption in the nanotube layers, but also provides a significantly reduced interface charge resistance at the nitride/metal interface due to subnitride (TaNx ) formation. As a result, such nanotube anodes afford a 15-fold increase of the photocurrent compared with conventional nanotubular Ta3 N5 electrodes under AM 1.5 G simulated sunlight (100 mW cm(-2)) conditions.

Growth of TiO2 Nanotube Layers on Ti Substrates with Different Microstructures

Since the reports on self-organized tubular oxide layers on Ti and its alloys by Assefpour-Dezfuly et al[1] and Zwilling et al[2,3], TiO2 nanotube layers have been widely studied in several application fields owing to its unique chemical and physical properties. It was reported that the morphology of the oxide layers is strongly influenced by anodization parameters such as electrolytic composition, applied voltage and electrolyte temperature. However, among the many anodization parameters, the influence of titanium substrate on oxide layer growth has not been clear yet. In the present study, the growth behavior of nanotubular oxide layers was examined by using Ti substrates with various microstructures. As-received Ti sheets (purity: 99.5%) were heat-treated at 500 °C for 12 h to ensure homogeneity. After the homogenization, some Ti sheets were heat-treated at various temperatures in argon atmosphere. Also, the other sheets were subjected to ARB (Accumulative Roll Bonding) process up to 6 cycles to change the microstructures. Anodization was carried out at 50 V for 3 h in ethylene glycol containing 2 wt% H2O and 0.05 M NH4F. After the anodization, the morphology of oxide layers was characterized by FE-SEM. Nanotubebular oxide layers were formed on all Ti sheets whereas the growth of nanotubular oxide layer was affected by the microstructure of Ti substrate that can be controlled by heat treatment and ARB process. The grain size increased with increasing heat-treatment temperature, duration while increasing the number of ARB cycle decreased the grain size. Consequentially, nanotubular oxide layer thickness increased with decreasing grain size. Therefore, it was found that the growth behavior may be affected by the numerous lattice defects in substrate introduced by heat-treatment and ARB process.

Zinc(II) Tetraphenylporphyrin Adsorption on Au(111): An Interplay Between Molecular Self-Assembly and Surface Stress

The interaction between zinc(II) tetraphenylporphyrin (ZnTPP) molecules and a Au(111) surface is investigated using scanning tunnel microscopy, from initial adsorption sites to monolayer self-assembly, with a particular emphasis on its relation to the surface atomic structure reorganization. At low coverage, no ZnTPP molecules are observed on terraces, and adsorbates appear to only decorate step edges. At intermediate coverage, ZnTPPs adsorb into self-organized islands of flat-lying macrocycles in quasi-registry with the underlying surface reconstruction, in areas delimited by herringbone reconstruction domain walls. At monolayer coverage, the adsorption geometry of the self-organized molecular layer can be fully characterized with respect to the atomic structure of Au(111) surface atoms. Moreover alteration of the Au(111) surface reconstruction domain size is observed, caused by an adsorbate-induced reduction of the Au(111) surface stress anisotropy. This behavior is not ubiquitous to ZnTPP monolayers as...

Electrochemical behavior and effect of heat treatment on morphology, crystalline structure of self-organized TiO2 nanotube arrays on Ti-6Al-7Nb for biomedical applications.

In the present work, we investigate the formation of self-organized titanium oxide nanotube layers by anodic oxidation on titanium alloy Ti-6Al-7Nb in electrolyte solution containing sulfuric acid and hydrofluoric acid. The anodized surface was characterized by micro-Raman, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS). The corrosion behavior of the treated and untreated samples was investigated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in simulated body fluid (Hanks' solution). The investigations show that the native oxide on the sample is replaced by self-assembled nanoarray by anodization. FESEM of samples annealed at 450 to 800 °C show tubular morphology whereas those annealed at 850 °C show collapse of nanotubes. Electrochemical impedance data of the substrate and 10 V anodized samples were fitted with a two-time constant equivalent circuit and that of anodized samples (20, 30 V) with a three-time constant equivalent circuit.

Self-organized TiO2 nanotube layer on Ti–6Al–7Nb for biomedical application

In the present study, a self-organized nanotube TiO2 layer on Ti–6Al–7Nb was fabricated. The influence of acidic electrolytes including glycerol (G) and ethylene glycol (EG) on the anodization, microstructural features and surface wettability was explored. The phase compositions and morphological characteristics were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. According to the results, due to the intrinsic amorphous feature of ceramic oxide, the characteristic TiO2 peaks were not detected in the XRD profiles. After annealing in normal atmosphere at 600°C for 2h, TiO2 crystallized and consequently, nanotubular TiO2 arrays containing anatase and rutile phases formed. From a microstructural point of view, the average length and diameter of the nanotube array ranged from 2.23 to 4.22μm and 160 to 170nm, respectively. Besides, the type of acidic electrolyte and subsequent annealing noticeably affected the surface wettability of the products.

Corrosion protection of iron using porous anodic oxide/conducting polymer composite coatings.

Conducting polymers (CPs), including polypyrrole, have attracted attention for their potential in the protection of metals against corrosion; however, CP coatings have the limitation of poor adhesion to metal substrates. In this study, a composite coating, comprising a self-organized porous anodic oxide layer and a polypyrrole layer, has been developed on iron. Because of electropolymerization in the pores of the anodic oxide layer, the composite coating showed improved adhesion to the substrate along with prolonged corrosion protection in a NaCl aqueous corrosive environment. The anodic oxide layers are formed in a fluoride-containing organic electrolyte and contain a large amount of fluoride species. The removal of these fluoride species from the oxide layer and the metal/oxide interface region is crucial for improving the corrosion protection.

Electrochemical behaviour and bioactivity of self-organized TiO2 nanotube arrays on Ti-6Al-4V in Hanks’ solution for biomedical applications

In the present work, the formation of self-organized titanium oxide nanotube layer by anodic oxidation on titanium alloy Ti-6Al-4V and its influence on growth of apatite on Ti-6Al-4V is reported. Anodization was carried out in sulfuric acid and hydrofluoric acid containing electrolyte and the anodized surface was characterized by micro-Raman, XRD and FESEM. The corrosion behavior of the anodized sample was investigated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in simulated body fluid (Hanks’ solution). The influence of TiO2 nano tubes on the growth of apatite on the anodized sample was investigated by immersion in Hanks’ solution for 1 and 7 days. The investigations show that the native oxide on the sample is replaced by self assembled nanotube array by anodization. The anodic oxide consist both anatase and rutile. After vacuum annealing at 600°C, intensity of rutile peak increased. FESEM of samples annealed at 450°C show tubular morphology whereas those annealed at 600°C show collapse of nano tubes. Corrosion resistance of the anodized sample was comparable with that of the untreated samples. Electrochemical impedance data of the substrate was fitted with two time constant equivalent circuit and that of anodized samples with three time constant equivalent circuit. FESEM images of immersed samples show that the growth of apatite is more with larger sized deposits on anodized surface as compared to that on the untreated substrate. XPS investigation of immersed sample shows presences of calcium, phosphorous and oxygen in hydroxide/phosphate form on the anodized sample.