Hyperbrenched 1-D Nanostructure For High Efficiency Dye Sensitized Solar Cells
Fabio Di Fonzo a, Luca Passoni a, Michael Graetzel b, Shaik Mohammed Zakeeruddin b, Fabrizio Giordano b
a Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, Via Pascol 70/3, Milan, 20133, Italy
b Ecole Polytechnique Federele de Lausanne, Laboratory of Photonics and Interfaces, CH-1015 Lausanne
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Poster, Fabio Di Fonzo, 206
Publication date: 1st March 2014

Hyperbranced TiO2 nanostructures showing high scattering and light trapping were recently reported as photoanodes for solid state DSCs with high power conversion efficiency (PCE)1. In this work hyperbranced quasi-1D tree-like structures, grown by self-assembly on a glass-SnO:F substrate at room temperature by Pulsed Laser Deposition (PLD), are optimised for high efficiency liquid electrolyte DSCs. The effects of morphological parameter of optically optimized structures are herein investigated with high efficiency dyes. Large-size crystalline structures, formed by oriented attachment during thermal post–treatments, are tuned in size by changing the annealing time and temperature. Surface area available for dye chemisorption is maximised while preserving high degree of crystallinity and high intrinsic scattering cross section for visible light to enhance the optical thickness of the devices. Scanning electron microscopy, Raman spectroscopy and X-ray Diffraction Spectroscopy are used to gain insights about the photoanode morphology and crystalline phase and domain-size.

 A monotonic increase in crystalline grain-size and decreasing in surface area are observed with increasing annealing time and temperature. Benefits for the advanced light management of this material are observed as a broadband absorption extended to the near IR spectral region. High crystallinity, high surface area and outstanding optical properties lead to an overall power conversion efficiency ~9% in a 5 µm thick film without the need of additional scattering overlayer commonly employed in transparent mesoporous materials. These structures, that in principles could be fabricated with any materials with the only constrains of PLD solid target availability, can be though as efficient light managing scaffold for any kind of photovoltaic material spanning from dye-sensitized solar cells to perovskites. 


(Left) SEM cross-section of hyperbranched nanostructures 5 µm thick. (Right) Diffuse transmittance spectra of PLD fabricated nanostructures compared to diffuse transmittance spectrum of a standard mesoporous film.
Passoni, L.; Ghods, F.; Docampo, P.; Abrusci, A.; Martí-Rujas, J.; Ghidelli, M.; Divitini, G.; Ducati, C.; Binda, M.; Guarnera, S.; Li Bassi, A.; Casari, C. S.; Snaith, H. J.; Petrozza, A.; Di Fonzo, F., Hyperbranched Quasi-1D Nanostructures for Solid-State Dye-Sensitized Solar Cells. ACS Nano 2013, 7 (11), 10023-10031.
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