Impedance Analysis of CdSe Quantum Dot-Sensitized TiO2 Solar Cells Decorated with Au Nanoparticles and P3OT

• Published in: Journal of the Electrochemical Society 2014-01, Vol.161 (3), p.H68-H74
• Main Authors: Zarazúa, I., López-Luke, T., Reyes-Gómez, J., Torres-Castro, A., Zhang, J. Z., De la Rosa, E.
• Format: Article
• Language: English
• ISSN: 0013-4651
• DOI: 10.1149/2.012403jes

Electrochemical impedance spectroscopy was used to analyze 10 μm thickness TiO2 films containing 250 nm TiO2 nanoparticles (NPs) with anatase crystalline phase deposited on FTO substrates. The TiO2 films were sensitized with CdSe quantum dots (QDs) (4.5 nm) and decorated with Au nanoparticles (NPs) (7 nm) and poly-3-octylthiophene (P3OT) in three different configurations, namely TiO2/QDs, TiO2/Au/QDs, and TiO2/Au/QDs/P3OT. The characteristic absorption bands for each component, TiO2, P3OT, CdSe QDs, and Au NPs, are centered at 338 nm (3.67 eV), 459 nm (2.7 eV), 552 nm (2.24 eV), and 517 nm (2.40 eV), respectively. The UV-Vis spectrum of the composite film TiO2/Au/QDs/P3OT shows clear absorption peaks from 338 to 700 nm. Equivalent circuits were proposed for the different configuration interfaces to fit experimental impedances. The results suggest that the introduction of Au NPs into the TiO2/Au/QDs films strongly reduces resistance to the electron flux from QDs to TiO2 and increases the overall charge transport. Meanwhile, P3OT in the TiO2/Au/QD/P3OT films promotes hole transport and increases the capacitance with the electrolyte, reducing the electron leakage and improving the fill-factor and the final light energy conversion efficiency.