Gelation of solvent-free electrolyte using siliceous materials with different size and porosity for applications in DSSC

Vittoria Sacchetto^a, Leonardo Marchese^a, Chiara Bisio^a, Chiara Vittoni^a, Daniele Costenaro^a, Simone Mastroianni^b, Andreas Hinsch^b

^aUniversity of Eastern of Piedmont

^bFraunhofer Institute for Solar Energy Systems ISE, Germany, Heidenhofstraße, 2, Freiburg im Breisgau, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Daniele Costenaro, 413
Publication date: 5th February 2015

Dye-sensitized solar cells (DSSC) are attracting the interest of the scientific community due to their potential advantages of high efficiency and low cost¹. Recent studies have shown that the use of a gel- or quasi-solid electrolyte-based DSSC, commonly obtained by adding to nitrile-based electrolytes or ionic liquid mixture solid particles with different chemical nature, led to a significant increase in energy-conversion efficiency and long term stability. Quasi-solid electrolytes were obtained by adding to liquid electrolytes solid particles with different chemical nature as synthetic saponite clays², alumina³ and silica nanoparticles⁴. Nevertheless, in many cases, a try-and-test approach is used to select the most promising solid for DSSC purposes. In our approach, solids with controlled properties (i.e. textural and morphological features) and chemical composition have been selected to understand the role of nanoparticles in the final performances of DSSC devices. Particular attention was given to the modification of particle size of prepared solids, aiming at obtaining good suspensions in liquid electrolytes and to optimize the interaction with TiO₂ semiconductor. From the other side, the surface of silica solids were properly modified in order to introduce a basic group, because of its positive effect on the final performances of the DSSC devices⁵. Interesting results were obtained by using silica particles as additives for DSSC devices. Three different silica-based materials were synthetized: monodispersed silica particles with different size (prepared by Stoeber and water-in-oil microemulsion methods) and porous ordered mesostructured silica (MCM-41). In addition organo-silica materials, containing basic –NH₂ species, were also prepared. The obtained solids were used for the preparation of quasi-solid electrolytes by dispersing 15wt.% of silica-based materials into an ionic liquid-based electrolyte. The electrochemical characterization of the cells based on quasi-solid electrolytes showed that the addition of all samples led to an increase of solar cell efficiencies. In particular, the electrolytes containing monodispersed silica particles with smallest dimensions (ca. 50 nm) showed an increase of ca. 14% of the overall efficiency. An accurate electro-chemical characterisation was performed in order to understand the role of additives in the final performances of DSSC cells. The measures of impedance spectroscopy showed that the silica nanoparticles added in the electrolyte in this study do not hinder significantly the charge diffusion resistancesin the electrolyte (Rd). In particular the reference devices show a Rd of 4.77 ohm, while the devices containing pure silica and functionalized silica display 5.38 ohm and 4.23 ohm, respectively. In addition, the light-beam-induced current (LBIC) mapping of current (Fig. 1 right) shows a good uniformity, this means that the silica particles do not alter the light harvesting properties of the DSSC devices.
Figure 1: Left side: J-V curves of DSSCs devices prepared by using reference electrolyte (-■-) and 15wt% gel-electrolyte prepared by adding bare silica samples (-●-) and amino functionalized silica nanoparticles (-▲-). EIS spectra are reported in the inset. Right side: LBIC of DSSCs devices prepared by using reference electrolyte and 15wt% gel-electrolyte prepared by adding bare silica samples and amino functionalized silica nanoparticles.
[1] O’Regan B.; Grätzel M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 1991, 353, 737-740. [2] Costenaro D.; Bisio C.; Carniato F.; Gatti G.; Oswald F.; Meyer T.B.; Marchese L. Size effect of synthetic saponite-clay in quasi-solid electrolyte for dye-sensititized solar cells. Solar Energy Materials & Solar Cells 2013, 117, 9-14. [3] Sacco A.; Lamberti A.; Gerosa M.; Bisio C.; Gatti G.; Carniato F.; Shahzad N.; Chiodoni A.; Tresso E.; Marchese L. Toward quasi-solid state Dye-sensitized Solar Cells: Effect of γ-Al2O3 nanoparticle dispersion into liquid electrolyte. Solar Energy 2015, 111, 125-134. [4] Wang P.; Zakeeruddin S. M.; Comte P.; Exnar I.; Grätzel M. Gelation of Ionic Liquid-Based Electrolytes with Silica Nanoparticles for Quasi-Solid-State Dye-Sensitized Solar Cells. J.AM.CHEM.SOC. 2003, 125, 1166-1167 [5] Etgar L.; Schuchardt, G.; Costenaro, D.; Carniato, F.; Bisio C.; Zakeeruddin S.M.; Nazeeruddin K.M.; Marchese L; Grätzel M. Enhancing the open circuit voltage of dye sensitized solar cells by surface engineering of silica particles in a gel electrolyte J. Mater. Chem. A, 2013, 1, 10142-10147.

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