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W2.02 - Dynamics of Semiconducting Nanocrystals Uptake into Mesoporous TiO2 Thick Films through Electrophoretic Deposition 
December 1, 2014   2:00pm - 2:15pm

An intense effort is boosting the development of third generation photovoltaic (PV) cells, to obtain cheap, high efficiency and environmentally friendly devices. One of the most promising solar cell architectures is based on quantum dots (QDs). The photoconversion efficiency (PCE) have reached to above 7%, by using near infrared (NIR) PbS QDs.[1] Electrophoretic deposition (EPD) has been demonstrated for preparation of high efficiency photo-anodes for QD solar cells, in which QDs are grafted to a mesoporous TiO2 NP thin film. As the performance of QD solar cell is highly dependent on not only the loading amounts, but also the QDs dispersion in TiO2 film, it is very important to control the QDs loading process.

Here, for the first time, we report a systematic investigation and modeling of the dynamics of NIR QDs loaded into TiO2 mesoporous film via EPD. We used PbS@CdS core@shell QDs and investigated the influence of EPD time, QD’s concentration and voltage on the QD uptake process via Rutherford backscattering for Pb depth profiling. The optical density of the obtained film is strongly dependent on the applied voltage, the deposition time and the concentration of solution containing the QDs. We modeled the deposition process using Fick’s diffusion law and explained the observed trends as a fast (and depth-independent) QD uptake induced by the presence of the electric field, followed by a diffusion-induced QD migration from outside the film, due to the fast creation of a QD concentration gradient. In addition, we demonstrated the increased stability of the core@shell structure compared to PbS QDs in terms of structure and optical property, based on X-ray photoelectron spectrometry and photoluminescence measurements. Thanks to the much higher stability of the core@shell QDs as compared to pure PbS QDs, our findings suggest that the PbS@CdS QDs loaded with EPD can be profitably used for the development of highly efficient and stable light absorbers in PV devices.

1 Salant, A.; Shalom, M.; Hod, I.; Faust, A.; Zaban, A.; Banin. “U. Quantum Dot Sensitized Solar Cells with Improved Efficiency Prepared Using Electrophoretic Deposition”, ACS Nano, 4, 2010, pp. 5962−5968

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