Mesostructured TiO2 films with ordered porous structure for photovoltaic devices

Gabriella Di Carlo^a, Chiara Giuliani^a, Gabriel Maria Ingo^a, Luisa De Marco^b, Roberto Giannuzzi^b, Giuseppe Gigli^b^,^c^,^d

^aISMN, Istituto per lo Studio dei Materiali Nanostrutturati, CNR, Via Salaria Km 29300, 00015, Monterotondo (Rome), Italy, Italy

^bCenter for Biomolecular Nanotechnologies (CBN), Fondazione Istituto Italiano di Tecnologia (IIT), Lecce, IT, Via Barsanti 1, Arnesano, 73010, Lecce, Italy

^cNational Nanotechnology Laboratory (NNL), CNR Istituto Nanoscienze, c/o Distretto Tecnologico, Via Barsanti, 73010 Arnesano , Lecce, Italy

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, Gabriella Di Carlo, 267
Publication date: 5th February 2015

Ordered mesoporous materials with high surface area, crystalline frameworks and tunable pore size have received extensive research attention because of their potential applications in many fields such as photocatalysis, sensors, energy storage and solar cells [1]. In particular, highly porous titania films with a well-defined size and geometry of the cavities are promising candidates to improve the performance of dye-sensitized solar cells (DSSCs) [2-3]. Mesostructured titania films prepared by a soft template assisted route are characterized by huge surface area, few grain boundaries and uniform pore structure with excellent connectivity of mesopores. All these features are key aspects in the preparation of titania-based photoanodes, since they affect the efficiency of the photovoltaic devices. Ordered mesoporous titania films also significantly improve the degree of dispersion of the adsorbed dye and increase the surface of dye/titania interface [4-5]. One of the most common routes for the production of mesoporous oxides with ordered mesostructure is the sol-gel synthesis in the presence of organic templates, such as triblock copolymers that have attracted great interest. These procedures offer many advantages, as low temperature, high scalability and low cost equipments. We thus have prepared novel mesostructured titania films and exploited their versatility to improve the performance of titania-based solar cells. Our recent findings have shown that bifunctional photoanodes with a double-scale morphology, which comprises a meso-ordered thin titania buffer layer and a main layer consisting of well-organized clusters of nanocrystallities, allow to achieve as high energy conversion efficiency as 9.7%. By using hierarchical mesostructured photoanodes, the DSSC efficiency was improved by 50.0% with respect to devices based on commercial P25 [6]. Highly ordered thin titania films, applied as an interfacial layer between the nanocrystalline main photoanode and the FTO electrode, suppress the back-transport reaction by blocking direct contact between the electrolyte and the transparent conductive oxide and provide excellent adhesion of the upper titania layer to the FTO. The main layer consists of hierarchical structures prepared by soft template assisted route and composed of nanocrystallites that cluster in well-organized larger secondary particles, thereby functioning as light scatterers without sacrificing the internal surface area which is indispensable for a good dye-uptake and light harvesting efficiency. Ordered mesoporous titania films have also shown promising performance in solid state devices.
Scanning electron microscopy image of a transparent titania thin film with an ordered pore structure
[1] Zhanga, R.; Elzatahryb, A. A.; Al-Deyabb, S. S;. Zhao, D. Mesoporous titania: From synthesis to application. Nano Today 2012, 7, 344-366. [2] Zukalova, M.; Zukal, A.; Kavan, L.; Nazeeruddin, M. K.; Liska, P.; Graetzel, M. Organized Mesoporous TiO2 Films Exhibiting Greatly Enhanced Performance in Dye-Sensitized Solar Cells. Nano Letters, 2005, 5, 1789-1792. [3] Dewalque, J.; Cloots, R.; Mathis, F.; Dubreuil, O.; Krinsad, N.; Henrist, C. TiO2 multilayer thick films (up to 4 µm) with ordered mesoporosity: influence of template on the film mesostructure and use as high efficiency photoelectrode in DSSCs, J. Mater. Chem. 2011, 21, 7356-7363. [4] Di Carlo, G.; Calogero, G.; Brucale, M.; Caschera, D.; de Caro, T.; Di Marco, G.; Ingo, G. M. Insights into meso-structured photoanodes based on titanium oxide thin film with high dye adsorption ability. Journal of Alloys and Compounds, 609, 2014, 116–124 [5] Di Carlo, G.; Caschera, D.; Toro, R.G.; Riccucci, C.; Ingo, G.M.; Padeletti, G.; De Marco, L.; Gigli, G.; Pennesi, G.; Zanotti, G.; Paoletti, A.M.; Angelini, N. Spectroscopic and Morphological Studies of Metal-Organic and Metal-Free Dyes onto Titania Films for Dye-Sensitized Solar Cells, International Journal of Photoenergy 2013, Article ID 582786, 11 pages. [6] De Marco, L.; Di Carlo, G.; Giannuzzi, R.; Manca, M.; Riccucci, C.; Ingo, G.M.; Gigli, G. Highly efficient photoanodes for dye solar cells with a hierarchical meso-ordered structure, Phys. Chem. Chem. Phys. 2013, 15, 16949-16955.

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