Linear-response Description of the Series Resistance of Large-area Silicon Solar Cells: Resolving the Difference between Dark and Illuminated Behavior

AbstractDirectly from luminescence images it can be shown that, for constant average injection (lumped dark current) and for not-too-large lateral voltage differences, besides the sign, the current flow direction doesn’t play any role for the voltages present, so the series resistances in the dark and under illumination are the same. This fits to the results of a linear-response based series resistance description, treating lateral voltage differences on large-area silicon solar cells in linear order in the series resistance as deviation from the case of zero resistance. In this approach it is found that for constant lumped dark current, emitter and grid of a large-area solar cell can be described as a passive network. Therefore, no difference occurs in the voltage distribution caused by inward and outward currents except for the sign. This contradicts several literature works reporting a smaller lumped series resistance of silicon solar cells in the dark than under illumination. However, we show that this contradiction is just a result of the series resistance definition applied in the respective works or that it can be the result of unsuitable measurement conditions. In a numerical modeling of a large-area silicon solar cell as a 1D distributed structure, using exactly the same parameters as Araújo et al. [IEEE-TED 33 (3), 391–401 (1986)] but calculating the lumped series resistance from the integrated Joule losses, we obtain completely different results than Araújo et al.: Under short-circuit condition, the series resistance stays constant, and there is no difference between the open-circuit and dark series resistance; the latter show the same dependence on the diode current density

Core-shell structured nets for biofouling control in aquaculture

This study demonstrates a robust, flexible interpenetrated composite based on 3D spined fabrics as core material and polydimethylsiloxane (PDMS) as shell material. The penetration of the shell component into the core material enables the mechanical interlocking at the micro and macro scale, providing mechanical stability and at the same time, introducing hydrophobic surface properties. Pure PDMS is a well-known biofouling-release material, showing drawbacks with respect to mechanical strength and adhesion-to-substrate, which can be overcome by the presented approach. Nowadays, antifouling strategies for aquaculture nets are realized by using biocide-containing coatings to avoid the attachment of organisms or repel them. Up to now, there are no coatings available on the market that provide adequate biofouling protection for aquaculture nets during the whole production cycle of the cultured stock. Even biocidal coatings exhibit a limited efficiency and need to be regularly cleaned, causing a substantial loss of the coating and increased emissions of biocides into seawater. This proof-of-concept study covers the scope from the design and production of the composite up to the first field tests in the Baltic Sea. The presented approach enabled by material science facilitates a fundamentally different approach in biofouling management and contributes to sustainable aquaculture

Light-Mediated Growth of Noble Metal Nanostructures (Au, Ag, Cu, Pt, Pd, Ru, Ir, Rh) From Micro- and Nanoscale ZnO Tetrapodal Backbones

Micro- and nanoscale ZnO tetrapods provide an attractive support for metallic nanostructures since they can be inexpensively produced using the flame transport method and nanoparticle synthesis schemes can take advantage of a coupled response facilitated by the formation of a semiconductor-metal interface. Here, we present a light-mediated solution-based growth mode capable of decorating the surface of ZnO tetrapods with nanostructures of gold, silver, copper, platinum, palladium, ruthenium, iridium, and rhodium. It involves two coupled reactions that are driven by the optical excitation of electron-hole pairs in the ZnO semiconductor by ultraviolet photons where the excited electrons are used to reduce aqueous metal ions onto the ZnO tetrapod as excited holes are scavenged from the surface. For the most part, the growth mode gives rise to nanoparticles with a roundish morphology that are uniformly distributed on the tetrapod surface. Larger structures with irregular shapes are, however, obtained for syntheses utilizing aqueous metal nitrates as opposed to chlorides, a result that suggests that the anion plays a role in shape determination. It is also demonstrated that changes to the molarity of the metal ion can influence the nanostructure nucleation rate. The catalytic activity of tetrapods decorated with each of the eight metals is assessed using the reduction of 4-nitrophenol by borohydride as a model reaction where it is shown that those decorated with Pd, Ag, and Rh are the most active

Tuning the Selectivity of Metal Oxide Gas Sensors with Vapor Phase Deposited Ultrathin Polymer Thin Films

Metal oxide gas sensors are of great interest for applications ranging from lambda sensors to early hazard detection in explosive media and leakage detection due to their superior properties with regard to sensitivity and lifetime, as well as their low cost and portability. However, the influence of ambient gases on the gas response, energy consumption and selectivity still needs to be improved and they are thus the subject of intensive research. In this work, a simple approach is presented to modify and increase the selectivity of gas sensing structures with an ultrathin polymer thin film. The different gas sensing surfaces, CuO, Al2O3/CuO and TiO2 are coated with a conformal 200 °C. The present study demonstrates possibilities for improving the properties of metal oxide gas sensors, which is very important in applications in fields such as medicine, security and food safety