Dynamics of semiconducting nanocrystal uptake into mesoporous TiO2 thick films by electrophoretic deposition

Year: 2015

Authors: Jin L., Zhao HG., Ma DL., Vomiero A., Rosei F.

Autors Affiliation: Inst Natl Rech Sci Energie Varennes, Varennes, PQ J3X 1S2, Canada; CNR INO SENSOR Lab, I-25123 Brescia, Italy; Lulea Univ Technol, S-97198 Lulea, Sweden; McGill Univ, Ctr Self Assembled Chem Struct, Montreal, PQ H3A 2K6, Canada.

Abstract: Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesoporous films, for example to graft semiconducting nanocrystals (quantum dots, QDs) on mesoporous oxide thick films acting as photoanodes in third generation solar cells. Here we study the uptake of colloidal QDs into mesoporous TiO2 films using EPD. We examined PbS@CdS core@shell QDs, which are optically active in the near infrared (NIR) region of the solar spectrum and exhibit improved long-term stability toward oxidation compared to their pure PbS counterpart, as demonstrated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. We applied Rutherford backscattering spectrometry (RBS) to obtain the Pb depth profile into the TiO2 matrix. EPD duration in the range from 5 to 120 min and applied voltages from 50 to 200 V were considered. The applied electric field induces the fast anchoring of QDs to the oxide surface. Consequently, QD concentration in the solution contained in the mesoporous film drastically decreases, inducing a Fick-like diffusion of QDs. We modelled the entire process as a QD diffusion related to the formation of a QD concentration gradient, and a depth-independent QD anchoring, and were able to determine the electric field-induced diffusion coefficient D for QDs and the characteristic time for QD grafting, in very good agreement with the experiment. D increases from (1.5 ± 0.4) x 10(-5) mu m(2) s(-1) at 50 V to (1.1 ± 0.3) x 10(-3) mu m(2) s(-1) at 200 V. The dynamics of EPD may also be applied to other different colloidal QDs and quantum rod materials for the sensitization of mesoporous films. These results quantitatively describe the process of QD uptake during EPD, and can be used to tune the optical and optoelectronic properties of composite systems, which determine, for instance, the photoconversion efficiency in QD solar cells (QDSCs).

Journal/Review: JOURNAL OF MATERIALS CHEMISTRY A

Volume: 3 (2)      Pages from: 847  to: 856

More Information: The authors are grateful to R. Milan and I. Concina for their support in the set-up of the EPD system, and to M. Chicoine and S. Roorda for their support in ion beam analysis. We acknowledge funding from NSERC in the f orm of Discovery Grants (D.M. and F.R.) and a Strategic Project Grant. F.R. is grateful to the Canada Research Chairs program for partial salary support. This work was partially funded by MDEIE through the international project WIROX. H.Z. is grateful to NSERC for a personal post-doctoral fellowship. A.V. thanks the European Commission for an individual Marie Curie Fellowship under contract no. 299490 and partial support under EC contract WIROX no. 295216. F.R. acknowledges NSERC for an E.W.R. Steacie Memorial Fellowship.
KeyWords: Sensitized Solar-cells; Quantum-dot Photovoltaics; Optical-properties; Pbs; Dye; Ligand; Size; Photosensitization; Electrodes
DOI: 10.1039/c4ta05549g

Citations: 31
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