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4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 277 Figure 1 ESI-MS spectrum of the binuclear species (A), the absorption spectra in dimethylformamide (B), the HOMO and LUMO orbitals (C) and CVs in 0.1 mol L-1 (n-Bu4N)ClO4 in DMF, using Pt-disk working and Ag/AgNO3(0.010M in acetonitrile) reference electrode (D). Molecular modeling using ZINDO/S and Molecular Mechanics 2 showed that visible bands were charge-transfer transitions centered on the [RuCl(dmbpy)2(BPEB)] and [RuCl(dcbpyH2)2(BPEB)] moieties. Also, the LUMO is centered on the dcbpy and BPEB π*orbitals (Figure1C) which may allow Ru II (dmbpy)2Cl-to-dcbpy(π*) charge-transfer transitions. A careful analysis of the spectrum showed that dmbpy complex has a slightly higher MLCT excited state than the dcbpy complex allowing energy transfer processes. In addition, the HOMO is localized on the [RuCl(dmbpy)2(BPEB)] complex, confirming the oxidation of the dmbpy complex at lower potentials than the dcbpy complex. Thus, the holes generated by electron injection from the [RuCl(dcbpyH2)2(BPEB)] moiety can be rapidly transferred to the [RuCl(dmbpy)2(BPEB)+ group (∆E=0.44V) which potential is suitable for fast hole transfer to the redox electrolyte, thus inhibiting electron-hole recombination processes. References [1] Argazzi, R.; Murakami Iha, N. Y.; Zabri, H.; Odobel, F.; Bignozzi, C. A., "Design of molecular dyes for application in photoelectrochemical and electrochromic devices based on nanocrystalline metal oxide semiconductors". Coord. Chem. Rev. 248(13–14),1299-1316(2004). [2] Nogueira, A. F.; Toma, S. H.; Vidotti, M.; Formiga, A. L. B.; Cordoba de Torresi, S. I.; Toma, H. E., "A highly efficient redox chromophore for simultaneous application in a photoelectrochemical dye sensitized solar cell and electrochromic devices". N. J. Chem. 29(2),320-324(2005). [3] Toma, S. H.; Uemi, M.; Nikolaou, S.; Tomazela, D. M.; Eberlin, M. N.; Toma, H. E., "{trans-1,4-Bis[(4pyridyl)ethenyl+benzene}(2,2‘-bipyridine)ruthenium(II) Complexes and Their Supramolecular Assemblies with β- Cyclodextrin". Inorg. Chem. 43(11),3521-3527(2004). © SEFIN 2012
4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 278 C137 - Temperature dependence of transport-properties of spiro-MeOTAD as a holeconductor in solid-state dye-sensitized solar cells Amalie Dualeh, Thomas Moehl, Mohammad K. Nazeeruddin, Michael Grätzel Ecole Polytechnique Federale de Lausanne, Station 6, EPFL-SB-ISIC-LPI, Lausanne, 1015, CH In solid-state dye-sensitized solar cells the liquid electrolyte is replaced by a solid hole– transport material (HTM) to improve the processability and long-term stability of the devices. As such it is vital to gain a thorough understanding of the transport-properties of the chosen HTM to determine the resulting impact on the device performance. Electrical impedance spectroscopy (EIS) is a useful technique to investigate the internal electrical processes occurring at different conditions of steady-state in the dark of complete devices. In this work the internal transport and recombination parameters of ssDSCs using the HTM 2,2’,7,7’tetrakis(N,N-di-p-methoxy- phenylamine)-9,9’-spirobifluorene (spiro-MeOTAD) were studied using EIS. Recent studies investigated the charge-transport properties of thin films of thermally evaporated spiro-MeOTAD [1,2]. Conversely, here we examined the properties in actual working configuration. To achieve this, ssDSC-like devices were fabricated using flat and nano-structured TiO2 and compared to devices using nano-structured ZrO2 to differentiate between the transport processes within the different elements in the ssDSC. The effect of chemical p-doping the HTM on the transport within the HTM was investigated and its temperature dependence was examined and analyzed using the Arrhe- nius equation. Using this approach the activation energy for the hole–hoping transport within the spiro-MeOTAD films was determined. References [1] Rana, O.; Srivastava, R.; Grover, R.; Chauhan, G.; Bawa, S. S.; Zulfequar, M.; Husain, M.; Kamalasanan, M. N.; "Charge Transport Study of 2,2’,7,7’-Tetrakis( N, N-di-4-methoxyphenyl amino)-9,9’- spirobifluorene Using Impedance Spectroscopy". Jpn. J. Appl. Phys. 50, 061601 (2011). [2] Rana, O.; Srivastava, R.; Grover, R.; Zulfequar, M.; Hu- sain, M.; Kamalasanan, M. N.; "Charge transport studies in thermally evaporated 2,2,7,7-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9- spirobifluorene (spiro-MeOTAD) thin film". Syn. Metals 161, 828–832 (2011). © SEFIN 2012
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