Fluorous molecules for dye-sensitized solar cells: synthesis and photoelectrochemistry of unsymmetrical zinc phthalocyanine sensitizers with bulky fluorophilic donor groups

Two sterically hindered zinc phthalocyanines bearing fluorous alkoxy substituents and carboxylic acid groups acting respectively as electron donor and electron acceptor/anchoring units, were synthesized and their ability to photosensitize nanocrystalline TiO2 films was investigated. The electronic properties of these new dyes were characterized by combining UV-vis spectroscopy, electrochemical techniques and DFT computation. Nanocrystalline TiO2 electrodes treated with the fluorous dyes were assembled in dye-sensitized solar cells (DSCs) and further characterized by photocurrent action spectroscopy, photocurrent-photovoltage measurements and electrochemical impedance spectroscopy. The maximum photon-to-current conversion efficiencies (IPCE) in the near IR region compared favorably with those achieved with some of the best phthalocyanine dyes investigated so far, thus highlighting the potential of fluorousmolecules as DSC components. A maximum power conversion efficiency (?) of 1.3% was attained in the absence of any additive such as antiaggregating chenodeoxycholic acid or conduction band edge modifier tert-butylpyridine. The basic information gathered in this study will serve as guidelines for the design of new fluorous dyes for highly efficient DSCs.