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4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 147 C37 - Stable Dye-Sensitized Solar Cells Based on Nanosized Zeolites Dispersion in the TiO2 Layer Simone Guarnera a , Annamaria Petrozza b , Stefano Perissinotto b , Antonio Bonucci c , Guglielmo Lanzani b a, Politecnico di Milano, piazza Leonardo da Vinci 32, Milano, 20133, IT b, Center for Nano Science and Technology @Polimi Istituto Italiano di Tecnologia, via Pascoli 70/3, Milano, 20133, IT c, SAES Getters S.p.A., viale Italia 77, Lainate (MI), 20020 , IT Dye-sensitized solar cells (DSSCs) are a promising technology for a variety of applications and long term stability is an essential feature to wide commercialization [1]. In particular, water infiltration inside the cell has been found as one of the main cause of efficiency degradation [2]. Permeation can be reduced by barrier layers, but most of the time, good quality barriers increase the cost and/or the weight of the device. To address this problem we propose, as an alternative solution, the use of integrated getter [3]. We have dispersed inside the mesoporous TiO2 layer, LTA-Na zeolites (300nm nanoparticles), a well known class of moisture getters that are able to absorb moisture; in this way water molecules that can get through the sealant and infiltrate inside the cell are neutralized. These particles are already introduced in the first fabrication steps and they are activated during the sintering process of TiO2 porous substrates. Therefore they can protect the cell already during the fabrication process when they are not shielded from the external world by any kind of barrier. The optical properties of this innovative structure have been first investigated. We found that these particles are efficient light scattering centers, therefore, though the dye loading in presence of the nanozeolites is lower, these substrates present a gain in terms of light absorption. Then, these unconventional substrates have been tested as photoanodes in working DSSCs. Performances are almost unchanged in presence of nanozeolites while aging tests show a clear and encouraging improvement of the devices stability. References [1] Asghar, M. I.; Miettunen, K.; Halme, J.; Vahermaa, P.; Toivola, M.; Aitola, K.; Lund, P. "Review of stability for advanced dye solar cells". Energy Environ. Sci. 3, 418–426 (2010). [2] Agrell, H. G.; Lindgren, J.; Hagfeldt, A. "Degradation mechanisms in a dye-sensitized solar cell studied by UV–VIS and IR spectroscopy". Solar Energy 75, 169–180 (2003). [3] Bonucci, A.; Macchi, R.; Giannantonio, R. Patent No WO2011076492 © SEFIN 2012
4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 148 C38 - A new electrical model for the analysis of partially shaded dye solar cell modules Roberto Giannuzzi, Michele Manca, Giuseppe Gigli Italian Institute of Technology, via Barsanti 1 , Arnesano (LECCE), 73010, IT Partial shading is a commonly encountered mismatch problem in a photovoltaic system. In the drawing near perspective of their massive building integration, dye solar cell (DSC) modules may realistically receive different levels of irradiance, a situation similar to partial shading. In these conditions, the electrical characteristics of the DSC module change significantly. To date only few studies about the effect of the partial shadowing on the photovoltaic characteristics of DSC module have been reported. In such reports the electrical behavior of the cell in forward bias is described by means of a model based on the continuity equation (or more specifically by means of the diode equation) whereas the Butler–Vollmer model is generally used to describe the cell in reverse bias conditions. 1-2 Starting from these remarks, we have been focused on the elaboration of a more accurate analytical model capable to adequately describe the I-V characteristics of a DSC module even when it is operating upon partial shadowing conditions. In particular we intended to modify the one diode equation equivalent circuit model of a photovoltaic cell by properly introducing a second diode in order to conveniently take into account the cell’s electrical behavior even in reverse bias conditions. Such a two-diode model has been thus implemented to examine the photovoltaic behavior of a DSC module constituted by four series elements in the case in which one (or more) of them resulted partially or totally shadowed. 3 Figure 1 left) I-V characteristics of a 4-cells module with 0, 2 and 3 fully shadowed cells . right )Equivalent electrical circuit based on the two-diodes model In this work the experimental I-V characteristics measured under systematically different illumination conditions have been investigated and compared with the corresponding simulated plots as obtained through the implementation of the above referred two-diodes based equivalent circuit. A perfect matching between the experimentally measured I-V characteristics and the simulation results, as obtained through the implementation of the twodiodes-based model, has been revealed. It has to be also highlighted that our approach has recourse to a significantly less number of physical and chemical parameters with respect to the previously proposed models, that makes it definitively more reliable and effective. © SEFIN 2012
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