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Pumiglia D.,University of Rome La Sapienza | Giustini M.,University of Rome La Sapienza | Dini D.,University of Rome La Sapienza | Decker F.,University of Rome La Sapienza | And 6 more authors.
ChemElectroChem | Year: 2014

TiO2-based dye-sensitized solar cells (DSSCs) sensitized with the Ru-dyes N719 and Z907, are subjected to prolonged reverse bias (RB) by imposing a constant current density of 25mAcm-2 for up to 1000h. The temporal changes of the DSSCs during the aging process are followed by the periodical recording of current-voltage curves, electrochemical impedance spectra, charge extraction measurements, and photovoltage decays at the various stages of cell aging. Beside the expected decrease in the concentration of I-3 during RB aging, the measurements show a surprising shift of the conduction band edge toward lower energies and a concomitant slowing down of the recombination process with the electrolyte for both DSSCs. This leads to a noticeable improvement in the energy conversion efficiency under low illumination conditions. These unexpected results are discussed on the basis of recent literature reports and attributed tentatively to the adsorption of H+ ions, which are produced during the RB aging, onto the TiO2 surface. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Galeotti M.,University of Rome Tor Vergata | Giammanco C.,University of Rome Tor Vergata | Giammanco C.,Center for Hybrid and Organic Solar Energy | Cina L.,University of Rome Tor Vergata | And 4 more authors.
IEEE International Symposium on Industrial Electronics | Year: 2014

In this work, we have characterized single nickel metal hydride (NiMH) cells with Electrochemical Impedance Spectroscopy (EIS) technique to determine online the state of the batteries. Studying the variations of the obtained impedance spectra at specific frequencies, which correspond to part of the spectra that change mostly during the charge and discharge processes of the batteries, we have constructed and interpreted diagnostic diagrams through a mathematical model based on Dempster-Schafer Theory of Evidence in order to determine the SOH. © 2014 IEEE. Source


Vesce L.,Center for Hybrid and Organic Solar Energy | Vesce L.,University of Rome Tor Vergata | Riccitelli R.,DYERS Srl | Soscia G.,Center for Hybrid and Organic Solar Energy | And 7 more authors.
Journal of Non-Crystalline Solids | Year: 2010

Titanium tetrachloride (TiCl4) treatment processed by chemical bath deposition is usually adopted as pre- and post-treatment for nanocrystalline titanium dioxide (TiO2) film deposition in the dye-sensitized solar cell (DSC) technology. Pre-treatment influences positively the bonding strength between the fluorinated tin oxide (FTO) substrate and the porous TiO2 layer, blocking the charge recombination at the interface between the conduction glass FTO and the I3 - ions present in the I-/I3 - red-ox couple. Additionally, TiCl4 post-treatment is a widely known method capable of improving the performance of dye-sensitized solar cells, in particular, the photocurrent collected from the device. In this study, the influence and effect of TiCl 4 pre- and post-treatment on the TiO2 layer is proposed and compared to the untreated film. The relative DSC devices are characterized in terms of short circuit current density, open circuit voltage, fill factor, conversion efficiency and IPCE. The dark current characteristics of cells with a treated and untreated TiO2 layer are also shown in order to evaluate the effect of TiCl4 pre-treatment as a blocking layer. © 2010 Elsevier B.V. All rights reserved. Source


Galeotti M.,University of Rome Tor Vergata | Cina L.,University of Rome Tor Vergata | Cina L.,Center for Hybrid and Organic Solar Energy | Giammanco C.,University of Rome Tor Vergata | And 5 more authors.
Energy | Year: 2015

Electrochemical energy storage has become important in the last years to improve the energetic efficiency of stationary and hybrid energy production systems. Lithium batteries represent the best choice, since they have high energy and power density, high number of cycles and a good temperature behaviour compared to other technologies. It becomes important the monitoring of the state of the battery to know online the energy content, to avoid dangerous operating conditions and to extend the useful life. In this work, we have defined a test procedure to study the ageing of LiPO (lithium polymer) batteries through the EIS (electrochemical impedance spectroscopy) technique. Through a fitting procedure performed on the acquired IS (impedance spectra), we have extracted the parameters of an equivalent circuit model to reproduce the voltage discharge curves of the batteries and to study the performance under load. Then we have introduced a relation between the ohmic resistance of the battery and the available capacity to evaluate the SOH (state of health) through the ToE (Theory of Evidence). The method is able to detect the SOH of the tested batteries with a maximum error of 3.73%, with an enhancement to 8.66% when an anomalous cell is considered. © 2015 Elsevier Ltd. Source


Galeotti M.,University of Rome Tor Vergata | Giammanco C.,University of Rome Tor Vergata | Giammanco C.,Center for Hybrid and Organic Solar Energy | Cina L.,University of Rome Tor Vergata | And 5 more authors.
Energy Conversion and Management | Year: 2015

The State of Health (SOH) of a battery is important to know the maximum energy that a battery can release while is operative and to plan the correct maintenance. In this work, we have implemented a diagnostic method to evaluate the SOH of single nickel metal hydride (NiMH) cells, that have an important role in power tools applications. Single NiMH cells of 1.2 V and 1.3 Ah have been characterized with Electrochemical Impedance Spectroscopy (EIS) technique to evaluate the SOH with synthetic methods. Through the study of an equivalent circuit model, we determine that three free parameters synthesize the information contained in an impedance spectrum. A new simplification allows us to construct a diagnostic diagram with only two degree of freedom. A mathematical approach based on the Dempster-Schafer Theory of Evidence has been implemented to interpret the diagnostic diagram. Combining the points obtained by the impedance spectra (IS) at different State of Charge (SOC) and SOH, the Theory of Evidence can improve the estimation of the SOH iteratively, a great advantage compared to the classic Theory of Probability. © 2014 Elsevier Ltd. All rights reserved. Source

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