Igor F. Vasconcelos

Flexible ITO-free organic solar cells applying aqueous solution-processed V2O5 hole transport layer: An outdoor stability study

Solution processable semiconductor oxides have opened a new paradigm for the enhancement of the lifetime of thin film solar cells. Their fabrication by low-cost and environmentally friendly solution-processable methods makes them ideal barrier (hole and electron) transport layers. In this work, we fabricate flexible ITO-free organic solar cells (OPV) by printing methods applying an aqueous solution-processed V2O5 as the hole transport layer (HTL) and compared them to devices applying PEDOT:PSS. The transparent conducting electrode was PET/Ag/PEDOT/ZnO, and the OPV configuration was PET/Ag/PEDOT/ZnO/P3HT:PC60BM/HTL/Ag. Outdoor stability analyses carried out for more than 900 h revealed higher stability for devices fabricated with the aqueous solution-processed V2O5.

Molecular modeling of iron and arsenic interactions with carboxy groups in natural biomass

Environmental context. Arsenic has been considered one of the most important global environmental pollutants. Its occurrence in water systems is a result of natural processes and anthropogenic activities. In view of their high toxicity and the consequent health problems associated with human exposure to contaminated waters and food, there is an increasing interest in the study of the specific interactions of arsenic species with organic matter. Here, specific interactions among arsenic, iron and a vegetable biomass are investigated with a view to demonstrate how these interactions can affect arsenic mobility in the environment. Abstract. The interaction of iron and arsenic with dried lettuce leaves was investigated using a combination of spectroscopic techniques. Iron binding to carboxy groups is indicated by a decrease of 84% in iron loading after esterification. According to extended X-ray absorption fine structure (EXAFS) analysis, FeIII is coordinated by six oxygen atoms (Fe–O distance of 1.98 A), two carbon atoms (Fe–C distance of 2.85 A) in a bidentate mononuclear form, and 0.5 or 1 arsenic atoms (Fe–As distance of 2.93–2.94 A). Arsenic is sorbed only when the biomass has been previously loaded with iron. AsV is coordinated by four oxygen atoms (As–O distance of 1.71 A) and one iron atom in a bidentate mononuclear form or two iron atoms (As–Fe distance of 2.93–2.94 A) in a bidentate binuclear form. In conclusion, the results demonstrate that carboxylic acid groups can affect AsV mobility in the environment so long as iron is available for bridging.

Structural disorder of ball-milled, nanosized, Fe-doped SnO2: X-ray diffraction and Mössbauer spectroscopy characterization

Structural characterization of nanosized Fe-doped semiconducting oxide SnO2 is reported. Samples of Sn1−xFexO2−y (with x ranging from 0.11 to 0.33) were processed in a planetary ball mill, subsequently HCl-washed to eliminate metallic iron impurities introduced by the milling tools, and characterized by X-ray diffraction and Mössbauer spectroscopy. Results showed that Fe enters the host matrix randomly replacing Sn in octahedral sites regardless of iron concentration. It has been found the presence of oxygen deficient iron sites attributed to the stoichiometric unbalance of precursor materials used in the milling process. It is known that structural features like particle size and residual microstrain are highly affected by the milling process. Values of average particle sizes as calculated by Scherrer’s method alone decreased with increasing Fe concentration. This result was shown, by means of the Williamson-Hall correction method, to be misleading as a large degree of microstrain is expected for mechanically milled powders. In fact, corrected values of average particle sizes turned out to be reasonably homogeneous regardless of iron content and milling time with no consistent trend. Residual microstrain, on the other hand, was found to increase with iron content giving way to the conclusion that broadening of diffraction peaks are mostly due to increasing microstrain as a function of iron doping and milling time. Williamson-Hall analysis also showed a large degree of particle size inhomogeneity. Milling of undoped SnO2 showed that this inhomogeneity is due mostly to doping as opposed to milling.

Structural, morphological and optical properties of SnO 2 nanoparticles obtained by a proteic sol–gel method and their application in dye-sensitized solar cells

Tin dioxide nanoparticles were synthesized by the proteic sol–gel method. Tin chloride (SnCl4·5H2O) was used as source of Sn4+ and commercial gelatin as organic precursor. Several calcination temperatures were employed. Thermogravimetric analysis and differential scanning calorimetry were performed to investigate the thermal behavior of the precursor powders as well as to select the appropriate calcination temperatures for oxide formation. Structural, morphological, and optical properties of the synthesized materials were studied by X-ray diffraction, transmission electron microscopy, Fourier transformed infrared spectroscopy, and ultraviolet–visible spectroscopy. The results confirmed the formation of spherical nanoparticles of rutile SnO2 with an optical absorption band in the ultraviolet region near the visible light range. Thermally treated samples showed improved crystallinity and superior transparency to visible light. These SnO2 nanoparticles were successfully employed as photoanode material in dye-sensitized solar cells. The performance of the cells was evaluated by measuring J × V curves in a solar simulator and was found to be in line with results in the literature.Graphical abstract

Synthesis and properties of Sn1−xFexO2 nanoparticles obtained by a proteic sol–gel method

Iron-doped SnO2 nanoparticles with chemical formula Sn1−xFexO2−y (x = 0.02, 0.05 and 0.10 at%) were successfully produced by a proteic sol–gel method. Thermogravimetric analysis and differential scanning calorimetry were performed to investigate the thermal behavior of the precursor powders as well as to select the appropriate calcination temperatures for oxide formation. X-ray absorption near-edge spectroscopy studies were carried out to determine the valence state of the transition metal used as dopant. Structural, morphological, and optical properties of the synthesized materials were studied by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectroscopy. The results confirmed the formation of nanometric spherical particles of single-phased SnO2 with rutile-type tetragonal structure. Iron doping was accomplished in the form of Fe3+ substituting for Sn4+ in the SnO2 matrix, with the creation of oxygen vacancies to achieve charge balance. Band gaps of SnO2 were found to be unaffected by the introduction of iron.

Chemical reactions of As complexation by glutathione: an XAFS study

In this study, the chemical reactions between As(III) and As(V) with glutathione, which is a target compound in As biochemistry due to its primordial role in As immobilization and intracellular reduction, in various molar ratios were investigated using As K-edge XAFS spectroscopy. Results showed a gradual substitution of As-O bonds in the coordination of aqueous As(III) and As(V) for three As-S bonds in the As+GSH complex. Moreover, the data showed reduction of As(V) to As(III) prior or concomitant to the As+GSH complex formation.

X-Ray Absorption Spectroscopy Applied to Metal Accumulation

X-Rays Absorption Fine Structure Spectroscopy (XAFS) is an analytical technique that can be used as a probe to characterize almost all elements, even if they appear in diluted or non-crystalline systems. This is due to the fact that the absorption probability of X-rays has a unique feature for each element, and is modulated by the chemical and physical state of that element, as well as by its neighborhood. This paper presents a brief description of the X-rays absorption phenomenon and the analytical technique involving this phenomenon, as well as the application of XAFS in biosorption studies. For more details on XAFS theory, refer to [1].