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Electron Transfer Dynamics in Dye-Sensitized Solar Cells Utilizing Oligothienylvinylene Derivates as Organic Sensitizers

Authors

  • John N. Clifford Dr.,

    1. L1.1.6 Laboratory, Institute of Chemical Research of Catalonia (ICIQ), Avda. Països Catalans 16, Tarragona 43007 (Spain), Fax: (+34) 977 920 200
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  • Amparo Forneli,

    1. L1.1.6 Laboratory, Institute of Chemical Research of Catalonia (ICIQ), Avda. Països Catalans 16, Tarragona 43007 (Spain), Fax: (+34) 977 920 200
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  • Leticia López-Arroyo,

    1. Instituto de Nanociencia, Nanotecnologia y Materiales Moleculares (INAMOL), Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, Toledo 45071 (Spain), Fax: (+34) 925 268 840
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  • Rubén Caballero,

    1. Instituto de Nanociencia, Nanotecnologia y Materiales Moleculares (INAMOL), Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, Toledo 45071 (Spain), Fax: (+34) 925 268 840
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  • Pilar de la Cruz Dr.,

    1. Instituto de Nanociencia, Nanotecnologia y Materiales Moleculares (INAMOL), Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, Toledo 45071 (Spain), Fax: (+34) 925 268 840
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  • Fernando Langa Prof.,

    1. Instituto de Nanociencia, Nanotecnologia y Materiales Moleculares (INAMOL), Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, Toledo 45071 (Spain), Fax: (+34) 925 268 840
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  • Emilio Palomares Prof.

    1. L1.1.6 Laboratory, Institute of Chemical Research of Catalonia (ICIQ), Avda. Països Catalans 16, Tarragona 43007 (Spain), Fax: (+34) 977 920 200
    2. Institució Catalana de Recerca i Estuids Avançats (ICREA). Avda. Lluís Companys, 28. Barcelona 08080. Barcelona (Spain)
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Abstract

Many dyes make light work: Molecular photovoltaic devices based on nanocrystalline TiO2 are prepared by using two dye sensitizers (see figure). Their relative efficiencies are greatly dependent on the molecular structures of the dyes.

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Two new organic dyes have been synthesized and used as efficient light-harvesting materials in molecular photovoltaic devices. These dyes are based on conjugated thienylvinylene units, with FL-4 consisting of a four-unit thienylvinylene oligomer and its homologue FL-7 which additionally incorporates the electron-donating triphenylamine unit (TPA) into its structure. Upon light excitation both dyes show efficient electron injection into the TiO2 conduction band and slow back electron transfer to the oxidized dye. In fact, for FL-7, the back electron transfer dynamics are slower owing to efficient hole transfer to the TPA moiety situated further from the semiconductor surface. However, the electron recombination kinetics with the oxidized electrolyte for both FL-4 and FL-7 in dye-sensitized solar cells are faster than for devices made using the ruthenium dye N719. We believe that this is a serious limiting factor for devices based on oligothiophenes which, despite showing higher molecular extinction coefficients in the vis-NIR region of the solar spectrum, still cannot challenge the light-to-energy conversion efficiency of N719 or other ruthenium polypyridyl complexes.

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