Dye-Sensitization of Tin Dioxide via the Functionalization of Oxide Surfaces with Trialkynylorganotins
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Dye-Sensitization of Tin Dioxide via the Functionalization of Oxide Surfaces with Trialkynylorganotins Thierry Toupance*,1 Mervyn de Borniol,1 Bernard Jousseaume,1 Gil Vilaça,1 Hubert Cachet,2 Vincent Vivier2 1 Laboratoire de Chimie Organique et Organométallique, UMR 5802 CNRS, Université Bordeaux 1, 351 Cours de la Libération, F33405 Talence Cedex, France. 2 Laboratoire des Interfaces et Systèmes Electrochimiques, UPR 15 CNRS, Université Pierre et Marie Curie, 4 Place Jussieu, 75 252 Paris Cedex 05, France.
ABSTRACT The surface modification of nanoporous tin dioxide materials was achieved with trialkynylorganotin(IV) (C4H9-C≡C)3Sn-(CH2)n(C10H20) (n = 4,6) 1 endowed with a perylene dye to yield powders containing up to 0.13 mmol.g-1 of perylene unit or dye-modified thin films. Irreversible chemisorption occurred in solution at room temperature to give perylene dye grafted at the oxide surface via the cleavage of the three tin-alkynide bonds of the precursor and the formation of Snbulk-O-Sn-Cdye linkages. The photoelectrochemical cells made with the 1-modified films demonstrated maximum incident photon to current efficiency (IPCE) as high as 18% at 430 nm under white light illumination. The performances of the cells were interpreted in terms of the intrinsic properties of tin dioxide and aggregation of the perylene dye.
INTRODUCTION Over the past decade, Grätzel et al. provided ample proof that dye-sensitized nanocrystalline semiconductor thin film solar cells were a potential cost-effective option to silicon-based cells [1], the most efficient systems being based on titanium dioxide, sensitized with ruthenium polypyridine complexes bearing carboxylic acid groups [2,3]. Among the available transparent semiconducting oxides, tin dioxide should be an interesting alternative to TiO2 since its more positive conduction band edge confers better electron acceptor properties and its larger band gap should impart better long-term stability under UV-light to the corresponding devices [4]. However, the more acidic character of SnO2 surfaces led to weak chemisorption of chromophores substituted with carboxylic acid functions, which drastically affects the efficiency and the stability of the related photoelectrochemical cells. Consequently, there is a strong need for new dye-oxide linkages to highlight both fundamental and practical advantages offered by SnO2. In this context, as tin is one of the rare metal atoms to form stable bond with carbon atoms, it should be possible to anchor covalently an organic dye onto SnO2 nanoporous materials via the formation of a stable Sn(oxide)-O-Sn-C(alkyl) linkage. Furthermore, we have recently shown that alkynylorganotins react with water or surface hydroxyl groups to yield oxides [5], hybrid materials [6] or modified silicas [7]. In the present study, we therefore report on the chemical modification of nanoporous SnO2 powders and thin films with (3-(ω-(trihex-1ynylstannyl)alkyl)perylenes 1 [8], the perylene core acting as the sensitizer (Scheme 1). The photoelectrochemical behavio
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