Assessment of new gem-silanediols as suitable sensitizers for dye-sensitized solar cells Gabriella Barozzino Consiglio a, b , Fabio Pedna a , Cosimo Fornaciari a , Fabrizia Fabrizi de Biani c , Gabriele Marotta d , Paolo Salvatori d , Riccardo Basosi c , Filippo De Angelis d , Alessandro Mordini a, b , Maria Laura Parisi c , Maurizio Peruzzini b , Gianna Reginato b , Maurizio Taddei e , Lorenzo Zani f, * a Dipartimento di Chimica “Ugo Schiff”, Università degli Studi di Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy b Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Florence, Italy c Dipartimento di Chimica, Università degli Studi di Siena, Via A. de Gasperi 2, 53100, Siena, Italy d Istituto di Scienze e Tecnologie Molecolari (CNR-ISTM), c/o Dipartimento di Chimica, Università degli Studi di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy e Dipartimento Farmaco-Chimico-Tecnologico, Università degli Studi di Siena, Via A. Moro 2, 53100 Siena, Italy f Istituto per la Sintesi Organica e la Fotoreattività (CNR-ISOF), Via Piero Gobetti 101, 40129 Bologna, Italy article info Article history: Received 1 September 2012 Accepted 4 October 2012 Keywords: Dye-sensitized solar cells Organic sensitizer gem-Silanediol Cyclic voltammetry TD-DFT calculations abstract Four novel gem-silanediol-containing organic dyes featuring a highly conjugated backbone have been synthesized in order to investigate their potential as active materials for photovoltaics. After spectro- scopic characterization, the compounds showing the best light harvesting and electrochemical proper- ties were applied as sensitizers in dye-sensitized solar cells (DSSCs). Interestingly, photovoltaic cells built using the new silanediol dyes showed low power conversion efficiencies (h), comparable to those ob- tained with silicon-based sensitizers having simple azobenzene moieties as the light-harvesting units. Such values are mostly due to unsatisfactory photocurrent densities; a computational study suggested that the latter can be justified considering the insufficient degree of charge transfer taking place during photoexcitation of the silicon-containing sensitizers, which is likely to make electron injection into the TiO 2 layer less efficient. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction In recent years, dye-sensitized solar cells (DSSCs) have attracted much attention as efficient and potentially low-cost alternatives to traditional silicon-based photovoltaic cells [1]. Initially, sensitizers employed in such devices have been mostly metallorganic compounds, in particular complexes of ruthenium with bipyridine or terpyridine ligands [2,3]; DSSCs fabricated with such dyes have reached solar-to-electric power conversion efficiencies (h) exceeding 11% [4]. More recently, a large number of metal-free organic dyes have also been introduced, and the corresponding solar cells have often displayed respectable power conversion efficiencies [5]. In a dye-sensitized solar cell, efficient attachment of the sensi- tizer to the semiconductor layer (most often constituted by TiO 2 ) is required to achieve smooth electron transfer between these two elements. Most of the organic dyes reported so far possess cyanoacrylic acid or rhodanine-3-acetic acid fragments as anchoring groups [5,6]; a smaller number of dyes has been reported, which are attached to the semiconductor by other func- tionalities, such as carboxylate [2], phosphonate [7], sulfonate [8], catechol [9] and pyridine [10] groups. Recently, a series of simple sensitizers having silicon-based anchoring groups was described by Unno, Hanaya and co- workers [11]. The choice of such anchoring functions was based on the fact that they form very strong bonds with a number of metal oxides, including titania [12], therefore potentially allowing the fabrication of highly stable photovoltaic cells. In those studies, the photovoltaic performances of DSSCs built with dyes 1aec, containing one or two azobenzene units, were compared with that of an analogous device fabricated using 4-carboxyazobenzene (2) as the sensitizer (Fig. 1). It was found that the power conversion efficiencies of devices containing compounds 1aec were higher than that of the cell containing compound 2, thus suggesting that dyes possessing a silicon anchoring function would yield more efficient solar cells than the corresponding carboxylic acids. However, the azobenzene unit is not an ideal chromophore for photovoltaic applications: first * Corresponding author. Tel.: þ39 051 6398301; fax: þ39 051 6398349. E-mail address: lorenzo.zani@isof.cnr.it (L. Zani). Contents lists available at SciVerse ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem 0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jorganchem.2012.10.012 Journal of Organometallic Chemistry 723 (2013) 198e206