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4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 255 C118 - Charge carrier dynamics in dye sensitized solar cells by diffuse reflectance spectroscopy Elham Ghadiri, Jacques-E Moser EPFL, EPFL SB ISIC GR-MO CH G0 627 (Bâtiment CH) Stati, Lausanne, 1015, CH Dye-sensitized solar cells (DSC) are a promising alternative to traditional inorganic semiconductor- based solar cells. Recently, their device performance has been increasing gradually, with a reported maximum efficiency of 12%. Pump-probe transient absorption spectroscopy is widely used to study the electron injection processes on model systems based on a transparent thin film, which is sensitized with dye [1]. Nanosecond flash photolysis technique also has been applied to study the electron back reaction and dye interception with electrolyte. However these techniques have been applied on dye sensitized transparent TiO2 mesoporous thin films as model systems. The high efficiency devices usually consistes of a scattering layer made of 400 nm TiO2 particles on top of a high surface area mesoporous transparent film, that makes the film optically opaque. Therefore current techniques cannot be applied to study the dynamic of reactions on the electrode itself and in the situation close to the situation of cell under operational conditions. Also other novel morphologies of TiO2, which show promising behaviour in cell performance, like nanowires and fibers [2,3], are not essentially transparent and cannot be studied by transient absorption pump probe in transmission mode. We have developed femtosecond diffuse reflectance spectroscopy technique to study the electron injection process on a DSC in the fashion applied in standard high efficiency devices. In these measurements the pump wavelength is set to the absorbance characteristic of the dye ground state and the probe wavelength corresponds to dye cation absorption. Two different dyes have been studied; first a well studied ruthenium based inorganic dye coded Z907 and a second D-π-A organic dye, coded Y123 which yielded a power conversion efficiency of over 10%. The results show an ultrafast electron injection in subpicosecond and a very fast decay of signal until some picoseconds and another decreasing component which happens in some hundered picoseconds. The later behaviour is not observed in the measurements of mesoporous transparent model system. Also the electron injection has been studied in the presence of Iodide and cobalt based electrolyte. References [1] B.Wenger, "Effect of electronic and nuclear factors on the dynamics of dye-to-semiconductor electron transfer", EPFL-3447, 170 (2006). [2] E. Ghadiri, N. Taghavinia, S. M. Zakeeruddin, M. Grätzel, J-E. Moser, "Enhanced electron collection efficiency in dye-sensitized solar cells based on nanostructured TiO2 hollow fibers", Nano Lett. 10, 1632-1638 (2010). [3] K. Shankar, J. Bandara, M. Paulose, H. Wietasch, O. K. Varghese, C. A. Grimes, "Highly Efficient Solar Cells using TiO2 Nanotube arrays Sensitized with a Donor-Antenna Dye", Nano Lett. 6, 1654-1659 (2008). © SEFIN 2012
4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 256 C119 - Chemically deposited polypyrrole-nanoparticle counter electrode for inorganic I-/I3- and organic T-/T2 dye-sensitized solar cells Madsakorn Towannang a , Samuk Pimanpang a , Anongnad Thiangkaew a , Phikun Rutphonsan a , Wasan Maiaugree a , Vittaya Amornkitbamrung a a, Department of Physics, Faculty of science, Khonkaen university, Khon Kean, 40002, TH b, Integrated Nanotechnology Research Center, Khon Kaen University, Khon Kean, 40002, TH c, Thaialnd Center of Excellence in Physics, CHE, Ministry of Education, Bangkok, 10400, TH Pure polypyrrole (PPy) and composited PPy-nanoparticles (multiwall carbon nanotube, Ni or TiO2) films were coated on the conductive glass by chemical deposition method. They were used as the dye-sensitized solar cell counter electrodes. The performance of polymer based dye-sensitized solar cells (DSSCs) is ~6.22% and ~2.81% for the I - /I3 - and T - /T2 electrolytes, respectively. The efficiencies increase greatly after nanoparticle incorporations for both electrolytes. PPy-MWCNTs DSSCs delivers the highest efficiency; ~6.56% and ~3.05% for the I - /I3 - and T - /T2 electrolytes, respectively. The improvement of the energy conversion efficiency after nanoparticle incorporation is attributed to the enlargement of the active surface area and the reduction of the charge-transfer resistance at the electrolyte/counter electrode interface. References [1] B. O'Regan and M. Grätzel, “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films”, Nature 353 (1991) [2] J. Wu, Q. Li, L. Fan, Z. Lan, P. Li, J. Lin, S. Hao, "High-performance polypyrrole nanoparticles counter electrode for dye-sensitized solar cells", J. Power Sources, 181, 172-176 (2008). [3] S. Peng, Y. Wu, P. Zhu, V. Thavasi, S.G. Mhaisalkar, S. Ramakrishna, "Facile fabrication of polypyrrole/functionalized multiwalled carbon nanotubes composite as counter electrodes in low-cost dyesensitized solar cells", J. Photochem. and Photobio. A: Chem., 223 97-102(2011). © SEFIN 2012
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