Effect of alkaline cation size on the performance of conductivity in gel polymer electrolytes suitable for dye sensitized solar cells

Maurizio Furlani^a, Bengt-Erik Mellander^a, T.M.W.J. Bandara^a^,^b, H.D.N.S. Fernando^a^,^b, Ingvar Albinsson^c

^aChalmers University of Technology, Sweden, Fysikgränd, 3, Gothenburg, Sweden

^bDepartment of Physical Sciences, Rajarata University of Sri Lanka

^cDeprtment of Physics, University of Gothenburg, Gothenburg

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, Maurizio Furlani, 325
Publication date: 5th February 2015

The nature and concentration of cationic species in the electrolyte exert a profound influence on the efficiency of nanocrystalline dye-sensitized solar cells [1]. In this work gel electrolytes suitable for dye sensitized solar cells (DSSCs) were studied using iodide salts (MI) with different cation sizes, namely the alkaline series LiI, NaI, KI, RbI, CsI. The electrolytes were fabricated according to the stoichiometric proportion (PAN)₁₀(EC)₂₅(PC)₂₀(MI)(I₂)_0.1where EC and PC represent ethylene carbonate and propylene carbonate respectively and the molar proportion of polyacrylonitrile(PAN) is relative to the polymeric repeating unit. The ionic conductivity of the electrolyte with large enough cations (K⁺, Rb⁺, Cs⁺) is more or less equal while for electrolytes containing Na+ and Li+ the ionic conductivity exhibits lower conductivity values respect to the other four electrolytes and these show is slightly lower or considerably lower, respectively. This behavior was consistent for all temperatures in the range from 0 °C to 60 °C. The electrolytes were used in DSSCs based on mesoporous nanocrystalline N719 stained TiO₂ sintered on FTO glass and having a platinized counter-electrode. The open circuit photovoltage (V_oc) of the cells increases with the cation radius. The enhancement in V_occan be attributed to the decrease in recombination of electrons in the conduction band of TiO₂and I₃⁻ in the vicinity of the TiO₂ electrode. The efficiency of the DSSCs also increases with the cation size and exhibits a maximum efficiency for the CsI containing sample thus in this work the efficiency of the DSSC has been governed by a dominant V_occhange. However, the highest short circuit photo-current density is shown by the RbI containing sample. The cation dependency of DSSC performance can be understood in terms of the co-ordination, intercalation and the adsorption of the cations at the nano-crystalline TiO₂ surface. Acknowledgement Authors wish to acknowledge the research support provided by Chalmers University of Technology, Gothenburg, Sweden and National Research Foundation Sri Lanka
Figure 1 shows a) the ionic conductivity of the electrolyte against cation type in the temperature range 0-60 °C, b) efficiency at 1 sun irradiance for DSSCs containing the alkaline iodide electrolyte series in the proportion (PAN)10(EC)25(PC)20(MI)(I2)0.1 where M = Li, Na, K, Rb, CS.
Watson, David F.; Meyer, Gerald J.; Cation effects in nanocrystalline solar cells. Coordination Chemistry Reviews 2004, 248, 1391–1406.

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