Plasmonic TiO2 thin films: interaction between Au nanoparticles and organic dyes for DSSC applications

Daniele Franchi^a^,^b^,^c, Massimo Calamante^a^,^c, Alessandro Mordini^a^,^c, Bengt-Erik Mellander^b, Maurizio Furlani^b, Lorenzo Zani^c, Gianna Reginato^c, Valeria Saavedra Becerril^d

^aDipartimento di Chimica “Ugo Schiff”, Università degli Studi di Firenze, Via della Lastruccia 13, Sesto Fiorentino, 50019, Italy

^bChalmers University of Technology, Sweden, Fysikgränd, 3, Gothenburg, Sweden

^cCNR - Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Via Madonna del Piano 10, Sesto Fiorentino, 50019, Italy

^dChalmers University of Technology, Sweden, Fysikgränd, 3, Gothenburg, Sweden

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Daniele Franchi, 424
Publication date: 5th February 2015

The introduction of metal nanoparticles into the nanoporous TiO₂ structure of the photoanode layer in DSSCs can result in enhanced photocurrent depending on the dye and the nanoparticle characteristics.^[1] The surface plasmon resonance phenomena due to the presence of gold nanoparticles (AuNPs) induces the plasmonic near-field absorption enhancement which allows the dye molecules located in their proximity to harvest more light; thus increasing the quantity of electrons injected in the semiconductor oxide layer resulting in improved photocurrent. Among the various systems studied so far, gold nanoparticles in combination with Ruthenium dyes have received increasing interest.^[2]2 thin films sensitized with purely organic dyes. AuNPs are able either to be excited and inject electrons to the TiO₂ conduction band (CB) or to be acceptors for electrons in the CB of TiO₂ ^[3] , the latter a loss process for the DSSC, increasing the recombination rate. Unfortunately gold is also sensible to corrosion if directly in contact with an iodine/triiodide-based electrolyte and might also promote recombination of the oxidized cationic dye with the injected electrons. These chemical and electronic interactions have been avoided creating a core-shell-shell Au-silica-titania system featuring an insulating silica shell creating a double Schottky barrier between the Au and the TiO₂.^[4] Specific methodologies ^[5] were used to build up a shell thinner than 10 nm so that only the near-field electromagnetic interaction between the plasmon and the dye was allowed. Semitransparent TiO₂ layers were needed to carry out the planned spectroscopic investigations. Thus highly homogeneous slurries of coated AuNPs/TiO₂ and different methods of deposition and annealing were tested to optimize thin semitransparent films towards the desired properties. Spectroscopic characterization was carried out in solution and in thin film samples. The extent of absorption enhancement was investigated in various mixtures of different organic dyes and AuNPs coated with different layers. Comparison with analogue, well-known, Ruthenium dyes was performed to investigate possible additional phenomena due to the presence of a dye metal center.

[1] Atwater, H. A.; Polman A. Plasmonics for improved photovoltaic devices. Nat. Mater. 2010, 9, 205-213. [2] Kawawaki, T.; Takahashi, Y.; Tatsuma T. Enhancement of Dye-Sensitized Photocurrents by Gold Nanoparticles: Effects of Plasmon Coupling. J. Phys. Chem. C 2013, 117, 5901–5907. [3] Primo, A.; Corma A.; García H. Titania supported gold nanoparticles as photocatalyst Phys. Chem. Chem. Phys. 2011,13, 886-910. [4] Mc Farland, E. W.; Tang, J. A Photovoltaic device structure based on internal electron emission. Nature 2003, 421, 616-618. [5] Sheehan, S. W.; Noh H.; Brudvig G. W.; Cao H.; Schmuttenmaer C. A. Plasmonic Enhancement of Dye-Sensitized Solar Cells Using Core–Shell–Shell Nanostructures. J. Phys. Chem. C 2013, 117, 927–934.

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