Plasma enhanced supersonic inseminated jet deposition of hierarchical nanostructures for dye sensitized solar cells.
Francesco Fumagalli a, Giorgio Nava a, Fabio Di Fonzo a, Luca Passoni a, Marco Monti b
a Istituto Italiano di Tecnologia, via Morego 30, Genova, 16163, Italy
b Politecnico di Milano, P.zza L. da Vinci 32 20133 Milan- Italy, Italy
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, Francesco Fumagalli, 208
Publication date: 1st March 2014

Dye sensitized solar cells (DSC) have been widely studied as promising and economical PV technology. The key reason preventing a technological breakthrough is their fairly low efficiency. In the last years research efforts have been focused on enhancing the performance by increasing the specific surface available for photoelectrochemical reactions and increasing charge collection and charge transport. As an example in a recent work [1], these issues were successfully tackled using photoanodes fabricated by PLD and based on novel hyperbranched nanostructures. Surface area was maximized for dye chemisorption while maintaining high degree of crystallinity and high scattering cross section for visible light, enhancing the optical thickness of the devices. Photoanodes based on structures displaying similar properties were also fabricated by new PECVD technique [2] allowing high deposition rate but still not capable of large scale fabrication.

In this communication we report about nanostructured thin film synthesis obtained coupling PECVD technique and inseminated sonic jet technique in a single reactor design for one-step, high yield deposition (1µm min-1) of TiO2 thin films with controlled porosity on large areas (100 cm2).This novel process is based on the segmentation of the gas phase material synthesis in two separate steps: (i) precursor dissociation chemistry control in a reactive plasma environment; (ii) nanoparticles nucleation and aggregation control by means of a sonic jet.The morphological properties of the ordered dendritic nanostructured films can be tuned, through plasma process parameters and aerosol gas dynamic of the sonic jet flow field, in order to tailor the optoelectrical properties of synthesised material. Such TiO2 photoanodes consisting of anatase single crystals assembled in quasi 1-D arrays of high aspect ratio hierarchical mesostructures are fabricated onto the F-doped SnO covered glass surfaces by self-assembly from the gas phase. Structural and morphological characteristics of TiO2 nanostructured photoanodes can be optimized to achieve simultaneously high specific surface area for optimal dye uptake and broadband light scattering. As an example of the efficacy of the new process, we present the results of the first functional tests on DSC.

A-C) Scanning electron microscope (SEM) cross sectional images of hierarchically nanostructured TiO2 photoanodes with different morphologies, porosity increases, from left to right, with the position of the substrate in the sonic jet flow field. D) SEM oblique view showing the global organization of nanostructured tree-like TiO2 nanostructures. E) SEM top view showing the spacing in between single nano-tree structures allowing easy dye and electrolyte infiltration F) Numerical simulation of the sonic jet flow field (units: Mach number).
[1] 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.; 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. [2] TrifilettiV.; Ruffo R.; Turrini C.; Tassetti D.; Brescia R.; Di Fonzo F.; Riccardi C.;Abbotto A. Dye-sensitized solar cells containing plasma jet deposited hierarchically nanostructured TiO2 thin photoanodes, J. Mater. Chem. A, 2013,1, 11665-11673.
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