Surface Modification in TiO2 Nanoparticle Layers by High Intense UV-Irradition for Dye Sensitized Solar Cells

Ulrich Hilleringmann^a, André Kleine^a

^aUniversität Paderborn, Warburger Str. 100, Paderborn, 33098, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, André Kleine, 281
Publication date: 5th February 2015

The efficiency of dye sensitized solar cells is strongly influenced by the quality of the front electrode. Therefore, the preparation of the front electrodes in high efficient dye sensitized solar cells usually need high process temperatures up to 450 °C to remove dispersal additives and to enable sintering effects. This leads to a reduction of the serial resistance caused by the limited electron transport inside the nano particulate TiO₂-layer, and to a better dye adherence. With the help of such high sintering temperature efficiencies up to 13 % are possible.[1] Nevertheless this temperature treatment is not applicable on ITO-covered foils used for flexible devices. Therefore, this paper presents a method to partly compensate this step by high intensive UV-exposure. UV-irradiation is a well-known process for surface cleaning. The proposed intense UV-irradiation for flexible low cost solar cells is roll-to-roll compatible, cleans the TiO₂-layer effectively and leads to a power gain due to surface activation. For the device integration Fluor-Tin-Oxide coated glasses were used as front and counter electrodes. The TiO₂-layer was built by a dip coating process using a dispersion based on Triton X-100, acetylacetone, polyethylene glycol and water. After drying at atmospheric conditions and structuring, a DSSC with an active area of 4 cm² and a TiO₂ thickness of ~7 µm is integrated. After the UV-irradiation the layer was sensitized using a hibiscus dye. A carbon layer deposited on the counter electrode functions as catalyst, and the electrolyte bases on an Iodide-/Triiodide redox couple. The UV-irradiation is performed by a 3000 W Xe Arc lamp. The substrates are placed in a distance of 20 cm for pulsed and permanent UV-irradiation. It can be shown, that a high intensive permanent UV-exposure removes the dispersal additives out of the TiO₂-layer. Furthermore permanent and pulsed irradiation are tested and compared. Additional to this cleaning steps the efficiency of the surface activation caused by the irradiation is presented. Therefor pre-sintered TiO₂-layers were irradiated before sensitizing. This step leads to a power gain of 25 % compared to non-irradiated cells (compare figure).
Comparison of the P/A-V-characteristics of irradiated and non-irradiated pre-sintered DSSC
[1] Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F E; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, Md K.; Grätzel, M. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nature chemistry 6 (2014), 3, 242-247.

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