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4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 253 C116 - Atomic level characterization of D35/TiO2 interfaces - co-sensitization and thermal degradation Johan Oscarsson a , Rebecka Schölin a , Susanna K Eriksson b , Kristofer Fredin c , Erik M. J. Johansson b , Håkan Rensmo a a, Department of Physics and Astronomy, Uppsala University, Box 516, Uppsala, SE-751 20, Sweden b, Department of Chemistry, Ångström, Uppsala University, Box 259, Uppsala, SE-751 05, Sweden c, Department of Applied Physical Chemistry, Royal Institute of Technology, Teknikringen 30, Stockholm, SE-100 44, Sweden To understand the performance of a dye in a dye‐sensitized solar cell (DSC) the properties of the surface molecular- and electronic structures are very important. Photoelectron spectroscopy (PES) gives information about binding geometry and energy levels in the dye molecules versus TiO2. The surface sensitivity of the method being in the order of 20 Å makes photoelectron spectroscopy a suitable tool for studies on the dye/semiconductor interface at an atomic level. Here we present results from studies on the sensitizer D35 regarding co-sensitization with a Ruthenium based dye (RD) as well as effects of thermal treatment on the molecular level. Co‐sensitization is used to improve the light harvesting efficiency of the DSC by utilizing dyes with different absorption properties. The study of D35 co‐sensitized with RD is based on two different approaches for dying the porous TiO2 electrodes. In the first the electrodes are first sensitized with RD and thereafter with D35 whereas the second approach relates to simultaneous adsorption of RD and D35 in a solution comprising a 2:1 concentration ratio of the respective dyes. The two dyes are clearly distinguishable in the PES measurements and the results give information of the adsorption dynamics and how different mixing affect the surface structure. Because the DSC preparation scheme may contain steps involving heat treatment (1) it is important to obtain information about the thermal stability of the utilized dyes. Here we present results on D35/TiO2 interfaces (dye-sensitized electrodes) subjected to elevated temperatures in an ambient air atmosphere. The results indicate that the dye molecules transform into a single new compound at higher temperatures, which may affect the performance of the DSC. The results also indicate that D35 can adsorb to TiO2 in different ways. Already at lower temperatures the relative amounts of the two kinds of adsorption are affected. References [1] Fredin, K.; Johansson, E. M. J.; Hahlin, M.; Schölin, R.; Plogmaker, S.; Gabrielsson, E.; Sun, LC. and Rensmo, H. “Solid state dye‐sensitized solar cells prepared by infiltrating a molten hole conductor into a mesoporous film at a temperature below 150 degrees C”. Synthetic metals 161, 2280-‐2283 (2011). © SEFIN 2012
4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 254 C117 - Block Copolymer Templated TiO2 Films in Extremely Thin Absorber Solar Cells Askhat Jumabekov a , Mihaela Nedelcu a , Laurence Peter b , Hiroaki Sai c , Ulrich Wiesner c , Thomas Bein a a, Fakultät Chemie und Pharmazie, Ludwig-Maximilians-Universität München, München, 81377, Germany b, Department of Chemistry, University of Bath, Bath, BA2 7AY, UK c, Department of Materials Science and Engineering, Cornell University, Ithica, NY 14853, USA Interest in ETA (extremely thin absorber layer) cells has increased steadily, but although performance values have improved progressively, 1 they are still well below the values that would be interesting for industrial production. 2,3 One of the main performance-limiting factors in ETA cells originates from the difficulty in finding suitable hole transporting materials (HTMs) that can provide complete pore filling and good charge transport. Key issues for further development of ETA cells include: 1) control of metal oxide structure in terms of pore size, surface area and crystallinity, 2) improvement of light harvesting, 3) improvement of HTM infiltration into the pores, 4) reduction of charge recombination and (5) enhancement of hole transport. Here we report the use of the structure-directing block-copolymer (BCP), poly(styrene-bethylene oxide) (PS-b-PEO), in preparation of porous TiO2 films for integration into ETA cells to enhance the porosity, crystallinity and structural regularity of the metal oxide layer. The porous TiO2 was obtained by mixing the BCP with a non-hydrolytic sol-gel, followed by annealing in air to remove the polymer and to transform the sol-gel into the pure crystalline anatase phase of TiO2. The porous TiO2 films obtained by this route were used in the fabrication of ETA solar cells in which a thin PbS absorber layer was deposited by the SILAR (successive ion layer adsorption and reaction) method, and the CuSCN HTM was infiltrated from solution phase by doctor blading. The performance of ETA cells based on these templated TiO2 films was compared with similar ETA cells made by sintering 25 nm sized P25 TiO2 nanoparticles. The comparison revealed that the use of BCP-templated porous TiO2 films improved the cell performance by a factor of 4 compared with the cells prepared using conventionally made porous TiO2 layers. The improvement of the device performance is attributed to higher BET surface area, enabling higher PbS uptake (better sensitization) and to the ordered pore structure, which results in better infiltration of the HTM. References [1] Dittrich, T; Belaidi, A; Ennaoui, A. "Concepts of inorganic solid-state nanostructured solar cells". Solar Energy Materials and Solar Cells, 95, 1527-1536 (2011). [2] Nezu, S; Larramona, G; Choné, C; Jacob, A; Delatouche, B; Péré, D; Moisan, C. "Light Soaking and Gas Effect on Nanocrystalline TiO2/Sb2S3/CuSCN Photovoltaic Cells following Extremely Thin Absorber Concept". The Journal of Physical Chemistry C, 114, 6854-6859 (2010). [3] Itzhaik, Y; Niitsoo, O; Page, M; Hodes, G. "Sb2S3-Sensitized Nanoporous TiO2 Solar Cells". The Journal of Physical Chemistry C, 113, 4254-4256 (2009). © SEFIN 2012
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