Irén Juhász Junger

Examination of the sintering process-dependent properties of TiO2 on glass and textile substrates

Abstract. In recent years, the development of smart textiles has attracted great attention. Such textiles can contain small electrical devices, which need a power supply. Dye-sensitized solar cells, which can be produced from nontoxic, cheap, low-purity materials, could fill this purpose. However, to reach reasonable cell properties, sintering the TiO2 layer on the substrate is necessary. Unfortunately, only a few textile materials can withstand a sintering process at high temperatures. Therefore, it is important to find an optimal temperature leading to a reasonable improvement of the cell characteristics without damaging the textile substrate. The influence of the sintering temperature on different properties is investigated. For this, the surface properties of the TiO2 coating, such as adhesion to the substrate, dye adsorption characteristic, and film stability, are investigated on different substrates, i.e., a glass plate, a stainless steel nonwoven fabric, and a carbon woven fabric. Two commercially available TiO2 sources are used: a TiO2 dispersion obtained from Man Solar and a water-based solution of TiO2 particles purchased from Kronos. The influence of the sintering temperature on short-circuit current and open-circuit voltage of solar cells on the aforementioned substrates is also examined.

Raising reproducibility in dye-sensitized solar cells under laboratory conditions

Dye-sensitized solar cells are subject to intensive research nowadays. Their open-circuit voltage, short-circuit current, and efficiency depend on several parameters which can be optimized. Here, examinations are limited to non-toxic substances due to planned future application on textile fabrics, i.e., to TiO2, graphite, and natural dyes. During experiments on the TiO2 layer, the reproducibility of the experiment turned out to be a crucial factor, limiting the significance of the experimental findings. Thus, the main goal of this paper is the description of possibilities to standardize the production under laboratory conditions by eliminating distorting factors. Specifically, the pressure by which the glass plates with conductive coatings, serving as electrodes, are pushed together to close the solar cell was found to significantly influence the results. Different possibilities were hence tested to normalize this pressure, including different clamps and magnets. In the optimal setup, the deviations betwe...

Washing and Abrasion Resistance of Conductive Coatings for Vital Sensors

In the area of medical textiles, several applications necessitate conductive sensors, such as ECG or pulse measurements, breathing sensors, etc. Additionally, connections between electronic elements, data transfer units, and other parts of sensor networks need conductive paths. The resistance of conductive yarns or coatings against mechanical and chemical influences, however, is often low. Silver particles in coatings or on yarns, e.g., can oxidize during washing. Thin coatings can easily be abraded and offer only a low conductivity due to low layer height, while thicker coatings can be stiff and break during bending. In a recent project, we evaluate different coatings with respect to their resistance against mechanical stress due to abrasion against diverse materials, as a typical demand of sensory shirts or other medical textiles. Conductive silicone rubber, as well as graphite-polyurethane dispersions with different graphite concentrations, were coated on diverse textile fabrics in a defined height. Abrasion tests were performed on these samples using a linear abrasion tester. The electrical resistance of the conductive coatings was measured after each test cycle. Additionally, confocal laser scanning microscopy was used to detect micro-cracks or modifications of the coating surface. The article gives an overview of the results and depicts the advantages and challenges of the conductive coatings under examination.

Dye-Sensitized Solar Cells with Electrospun Nanofiber Mat-Based Counter Electrodes

Textile-based dye-sensitized solar cells (DSSCs) can be created by building the necessary layers on a textile fabric or around fibers which are afterwards used to prepare a textile layer, typically by weaving. Another approach is using electrospun nanofiber mats as one or more layers. In this work, electrospun polyacrylonitrile (PAN) nanofiber mats coated by a conductive polymer poly(3,4-ethylenedioxythiopene) polystyrene sulfonate (PEDOT:PSS) were used to produce the counter electrodes for half-textile DSSCs. The obtained efficiencies were comparable with the efficiencies of pure glass-based DSSCs and significantly higher than the efficiencies of DSSCs with cotton based counter electrodes. The efficiency could be further increased by increasing the number of PEDOT:PSS layers on the counter electrode. Additionally, the effect of the post treatment of the conductive layers by HCl, acetic acid, or dimethyl sulfoxide (DMSO) on the DSSC efficiencies was investigated. Only the treatment by HCl resulted in a slight improvement of the energy-conversion efficiency.

Development of graphite-based conductive textile coatings

Conductive yarns and coatings are necessary for a broad variety of smart textile applications, such as sensors, data transmission lines, or heated fabrics. The main problems of such conductive textile elements are abrasion and washing resistance. Since different findings with respect to these properties are reported in the literature for similar coatings, the required optimization is impeded. In a recent study, the washing resistance of different graphite–polyurethane coatings with graphite contents between 25% and 33% on cotton, linen, viscose, and polyester woven fabrics was compared, using two different graphite particle sizes on diverse textile substrates. It was found that not only the graphite particle dimensions and graphite concentration strongly influence the longevity of the coatings, but also the textile substrates which were coated with the conductive mass. This means that conductive coatings cannot be optimized without knowledge of the planned application.

Spectral Analysis and Parameter Identification of Textile-Based Dye-Sensitized Solar Cells

Linearized equivalent electrical-circuit representation of dye-sensitized solar cells is helpful both for the better understanding of the physical processes in the cell as well as for various optimizations of the cells. White-box and grey-box modelling approaches are well-known and they are widely used for standard cell types. However, in the case of new cell types or the lack of deep knowledge of the cell’s physic such approaches may not be applicable immediately. In this article a black-box approach for such cases is presented applied together with spectral analysis. The spectral analysis and the black-box approach were as first validated with a standard glass-based dye-sensitized solar cell and thereafter applied for the characterization of a new type of textile-based dye-sensitized solar cells. Although there are still improvement potentials, the results are encouraging and the authors believe that the black-box method with spectral analysis may be used particularly for new types of dye-sensitized solar cells.

Influence of fabric pretreatment on adhesion of three-dimensional printed material on textile substrates

Adding three-dimensional printed objects on existing surfaces enables creation of multi-material objects with tailored mechanical properties. Especially, the tensile strength of a textile fabric is advantageous in comparison with three-dimensional printed polymeric parts, while the latter can increase the stiffness of the composite. The adhesion forces between both material partners, however, are crucial for the reliability of the multi-material object. While several printing and material properties have been shown to influence the adhesion previously, this article concentrates on the possible pretreatment methods for three-dimensional printing on a cotton fabric. In our experiments, we have shown that especially pretreatments which made the textile surface more hydrophobic or more hydrophilic resulted in significant modifications of the adhesion forces. In addition, the adhesion is influenced by the infill orientation, with an orientation of 90° being significantly advantageous compared to 0°. While surface roughness was also shown to depend on the infill angle, no significant differences of the tensile strength or the elongation at break were measured.