Fluorous Molecules for Dye-Sensitized Solar Cells: Synthesis and

Article pubs.acs.org/JPCC

Fluorous Molecules for Dye-Sensitized Solar Cells: Synthesis and Characterization of Fluorene-Bridged Donor/Acceptor Dyes with Bulky Perfluoroalkoxy Substituents Gabriela Marzari,† Javier Durantini,† Daniela Minudri,† Miguel Gervaldo,† Luis Otero,† Fernando Fungo,*,† Gianluca Pozzi,*,‡ Marco Cavazzini,‡ Simonetta Orlandi,‡ and Silvio Quici‡ †

Departamento de Química, Universidad Nacional de Río Cuarto, Agencia Postal No 3, X5804BYA, Río Cuarto, Argentina Istituto di Scienze e Tecnologie Molecolari del Consiglio Nazionale delle Ricerche, ISTM-CNR, via Golgi 19, 20133 Milano, Italy

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ABSTRACT: A series of structurally related sensitizers containing fluorene as a π-conjugated central core have been synthesized, characterized, and applied in the development of dye-sensitized solar cells (DSSCs). The new electron donor (diphenylamine)−acceptor (cyanoacrylic acid) D-π-A molecular structures hold perfluoro-tert-butyl substituents in different positions. It is demonstrated that the fluorous substitution pattern remarkably affects the behavior of dyes as photosensitizers in DSSCs, leading to an improvement in the power conversion efficiencies with respect to analogous nonfluorous molecules.

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INTRODUCTION The continuous growth of energy demand around the world and the environmental pollution resulting in global warming have led to a greater focus on research in renewable energy sources over the past decades. Contrary to the fossil fuels, solar energy is available profusely in most of the world’s regions; still, it can be used for direct electricity production by means of photovoltaic and photoelectrochemical cells. In this frame dyesensitized solar cells (DSSCs) are currently the most efficient and stable excitonic photocells,1,2 offering several advantages over traditional silicon-based devices, notably, simplicity in fabrication and reduction in production costs. These unique features give the chance to develop DSSC technology even in countries with lower industrialization levels. The design of suitable photosensitizers remains one of the most important research topics in DSSCs with regard for improving their performance.3 To this end a number of lightabsorbing compounds with different molecular structures have been proposed and tested,2 starting with Ru(II) polypyridyl complexes, which are still now one of the most successful class of photosensitizers.4 However, the limited availability of Ru and possible environmental problems could limit its extensive application. Furthermore, these complexes are relatively expensive and hard to purify compared with organic sensitizers that can be obtained at reasonable cost and high purity grade through well-established synthetic techniques. Organic dyes present other potential advantages, including the huge diversity of molecular structures and high molar extinction coefficients, generally superior to those of Ru dyes (