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(Invited) Photocurrent Enhancement of Quantum Dot Solar Cells By Plasmonic Metal Nanoparticles
Tetsu Tatsuma and Tokuhisa Kawawaki
Institute of Industrial Science, University of Tokyo
Komaba, Meguro-ku, Tokyo 153-8505, Japan
Noble metal nanoparticles absorb and scatter visible and near infrared light on the basis of localized surface plasmon resonance (LSPR). We found plasmon-induced charge separation (PICS)1,2 at the interface between plasmonic metal nanoparticles and semiconductor such as TiO2 and applied it to photoelectrochemistry. Another way of application of LSPR to photoelectrochemistry is based on a plasmonic enhancement effect.3 We have also examined the plasmonic enhancement effect on dye-sensitized solar cells, and found that there is the optimum distance between plasmonic nanoparticles and dye molecules4 and that enhancement is possible in the near infrared region by taking advantage of a plasmon coupling effect.5 Here we report a plasmonic enhancement effect of metal nanoparticles on quantum dot solar cells.
We prepared two-dimensional ITO/Au/TiO2/PbS electrodes.6 Au nanospheres were adsorbed onto a smooth ITO and coated them with a TiO2 thin film by a spray pyrolysis method. PbS quantum dots were prepared on the TiO2 surface using a successive ionic layer adsorption and reaction method through alternate spin-coating with aqueous Pb(NO3)2 and aqueous Na2S. Photocurrents were examined by using a two-electrode cell with the ITO/Au/TiO2/PbS electrode, a platinum-coated ITO counter electrode, and N2-saturated aqueous electrolyte containing Na2S. The photocurrents of the cell were enhanced in the wavelength range of 500-1200 nm by the Au nanospheres. The optimum quantum dot-nanosphere spacing was shorter and the maximum enhancement factor was higher when smaller quantum dots were used. This suggests that quenching via energy transfer from the PbS quantum dots to Au nanosphere is less significant for smaller quantum dots.
We also electrodeposited Au nanostars on an ITO electrode and coated them with a ZnO thin film. The nanostars generate strong optical near field at the tips. It was possible to control the plasmonic enhancement peak wavelength in the visible and near-infrared region by changing the deposition time.
In addition, we used Ag nanocubes for efficiency enhancement of a PbS quantum dot heterojunction cell. Ag nanocubes also generate strong optical near field at the corners and strong far field scattering. The location and amount of the nanocubes were optimized in terms of photocurrents and efficiency.
This work was supported in part by “R&D on Innovative PV Power Generation Technology” which The University of Tokyo contracted with New Energy and Industrial Technology Development Organization (NEDO) and a Grant-in-Aid for Scientific Research.
References
1. Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nature Mater., 2, 29 (2003).
2. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).
3. H. A. Atwater, A. Polman, Nat. Mater., 9, 205 (2010).
4. T. Kawawaki, Y. Takahashi, and T. Tatsuma, Nanoscale, 3, 2865 (2011).
5. T. Kawawaki, Y. Takahashi and T. Tatsuma, J. Phys. Chem. C, 117, 5901 (2013).
6. T. Kawawaki and T. Tatsuma, Phys. Chem. Chem. Phys., 15, 20247 (2013).