Cobalt-Based Electrolytes for Dye-Sensitized Solar Cells: Recent Advances towards Stable Devices

Redox mediators based on cobalt complexes allowed dye-sensitized solar cells (DSCs) to achieve efficiencies exceeding 14%, thus challenging the emerging class of perovskite solar cells. Unfortunately, cobalt-based electrolytes demonstrate much lower long-term stability trends if compared to the traditional iodide/triiodide redox couple. In view of the large-scale commercialization of cobalt-based DSCs, the scientific community has recently proposed various approaches and materials to increase the stability of these devices, which comprise gelling agents, crosslinked polymeric matrices and mixtures of solvents (including water). This review summarizes the most significant advances recently focused towards this direction, also suggesting some intriguing way to fabricate third-generation cobalt-based photoelectrochemical devices stable over time

Modeling potential-induced degradation (PID) in crystalline silicon solar cells: from acceleratea-aging laboratory testing to outdoor prediction

We present a mathematical model to predict the effect of potential-induced degradation (PID) on the power output of c-Si modules in different climates. For the experimental part, we manufacture mini-modules made of two c-Si p-type cells, and use accelerated ageing laboratory testing performed at different combinations of stress factors (temperature, relative humidity, and voltage). By modeling the effect of each stress factor in a step-wise approach, we obtain a model for the PID at constant stress conditions, which agrees well with models that can be found in the literature for full-size modules. Our model is obtained complementing existing models by introducing a term that describes a linear dependence of module’s power degradation on the magnitude of the applied voltage. Since in field installations PV modules are connected in strings and exposed to different potential – and, therefore, stress – levels, this latter term is needed to approach real field conditions. Finally, we present the first attempts to model PID outdoor degradation in different climate conditions based on the proposed model and on the indoor-determined coefficients for the devices tested. The outdoor prediction model makes use of Typical Meteorological Year (TMY) data for a specific location

Gas dynamics in tidal dwarf galaxies : disc formation at z=0

Tidal dwarf galaxies (TDGs) are recycled objects that form within the collisional debris of interacting/merging galaxies. They are expected to be devoid of non-baryonic dark matter, since they can form only from dissipative material ejected from the discs of the progenitor galaxies. We investigate the gas dynamics in a sample of six bona-fide TDGs around three interacting and post-interacting systems: NGC 4694, NGC 5291, and NGC 7252 ("Atoms for Peace"). For NGC 4694 and NGC 5291 we analyse existing HI data from the Very Large Array (VLA), while for NGC 7252 we present new HI observations from the Jansky VLA together with long-slit and integral-field optical spectroscopy. For all six TDGs, the HI emission can be described by rotating disc models. These HI discs, however, have undergone less than a full rotation since the time of the interaction/merger event, raising the question of whether they are in dynamical equilibrium. Assuming that these discs are in equilibrium, the inferred dynamical masses are consistent with the observed baryonic masses, implying that TDGs are devoid of dark matter. This puts constraints on putative "dark discs" (either baryonic or non-baryonic) in the progenitor galaxies. Moreover, TDGs seem to systematically deviate from the baryonic Tully-Fisher relation. These results provide a challenging test for alternative theories like MOND.Peer reviewe

Producción de helados funcionales

Análisis de mercado; Ingeniería; Marco legal; Análisis de costos; Análisis financiero; Conclusión; Anexos.Facultad de Ingenierí

Producción de helados funcionales

Análisis de mercado; Ingeniería; Marco legal; Análisis de costos; Análisis financiero; Conclusión; Anexos.Facultad de Ingenierí

Design of Experiments (DoE): a multivariate approach to dye-sensitized solar cells comprehension and optimization

Nowadays, modern science proposes and optimizes new materials and technologies, whose characteristics and performances are governed by many factors. However, the scientific community rarely adopts multivariate strategies for the comprehension of what is proposed. As a striking example, a standard dye-sensitized solar cell (DSSC) is a typical complex system assembled with different and heterogeneous layers (FTO/nanocrystalline semiconductor/sensitizer/electrolyte/Pt-FTO), each one affected by intrinsic variability; moreover the layers influence each other and this increases the number of variables involved at the same time in the photoconversion process. The idea of the present work started from the need to identify all the factors by which the photoconversion processes may be influenced. In order to obtain a significant improvement of photovoltaic performances, particularly in reproducibility, long-term stability and efficiency, a chemometric design of experiments (DoE) approach is here presented for four case studies: the formulation of a UV-cured polymer electrolyte membrane, the composition of a cellulose-based gel-polymer electrolyte, the proper sensitization of a ZnO photoanode and the photostability optimization of a series of NIR dyes under different dipping conditions. We are firmly convinced that this approach will make possible to find the optimal experimental conditions to achieve, within a good reproducibility, optimized performances, both in term of efficiency and long term stability

Aqueous photovoltaics: a new era in third generation devices

A key aspect still to be addressed in the DSSC community is the presence of water in the cell, either in the electrolyte or at the electrode/electrolyte interface. While it has been considered strongly harmful for a long time, in the last few years the scientific community suddenly turned the efforts in the direction of using water as a solvent, as demonstrated by the increasing number of research articles being published in the literature. Indeed, by means of DSSCs fabricated with water-based electrolytes, reduced costs, non-flammability, reduced volatility and improved environmental compatibility could be easily achieved. As a result, an increasing number of novel electrodes, dyes and electrolytes components are continuously proposed, being highly challenging from the materials science viewpoint and with the golden tread of producing truly water-based DSSCs. If the initial purpose of DSSCs was the construction of an artificial photosynthetic system able to convert solar light into electricity, the use of water as key component may represent a great step forward towards their widespread diffusion in the market. A starting point in this direction is given in this work, and a few curious and anomalous behaviours observed in the literature and in our laboratories are presented for this class of electrolytes. After a brief discussion of the current state of the art, this contribution proposes the investigation of both the stability of different classes of dyes (Ru complexes, squaraines, indolenines, carbazoles) in fully a aqueous environment, and the effect of the concentration of different iodine salts on the cell parameters and their stabilit