A significant improvement in the long-term stability for cobalt-based dye-sensitized solar cells (DSCs) under light-soaking conditions has been achieved by optimization of the composition of tris(2,2'-bipyridine) Co(ii)/Co(iii) electrolytes. The effects of component exchanges and changes were also studied during the optimization process.
Recently, cobalt redox electrolyte mediators have emerged as a promising alternative to the commonly used iodide/triiodide redox shuttle in dye-sensitized solar cells (DSCs). Here, we report the successful use of a new quasi-liquid, polymer-based electrolyte containing the Co(3+)/Co(2+) redox mediator in 3-methoxy propionitrile solvent in order to overcome the limitations of high cell resistance, low diffusion coefficient and rapid recombination losses. The performance of the solar cells containing the polymer based electrolytes increased by a factor of 1.2 with respect to an analogous electrolyte without the polymer. The performances of the fabricated DSCs have been investigated in detail by photovoltaic, transient electron measurements, EIS, Raman and UV-vis spectroscopy. This approach offers an effective way to make high-performance and long-lasting DSCs.
Constantly increasing energy demand has led to much attention being devoted to converting abundant solar energy to electricity. Dye-sensitized solar cells (DSCs) are a promising technology for renewable energy, thanks to their low cost, ease of fabrication, and good conversion efficiency. 1, 2 Solar cells work well only in good light intensity, but light levels vary throughout the day and are low indoors. DSCs have the advantage of working relatively well even in diffuse lights, which is good for practical and indoor applications. However, it would be good to improve their efficiency further at low light levels. Recently, redox mediators based on [Co(bpy) 3 ] 2+/3+ (where Co is cobalt and bpy is 2,2'-bipyridine) have emerged as promising redox couples that offer high photon-to-electron conversion efficiencies and high photovoltages: see Figure 1. 3, 4 However, these redox couples display a few electrolyte problems, such as high cell resistance, a low diffusion coefficient, and rapid recombination loss rates. To overcome these limitations, we have introduced an ion-conducting polymer into DSC electrolytes. Polymers with a high dielectric constant, such as poly(vinylidine fluoride) (PVDF), may help ionization of salts, and hence provide high concentrations of charge carriers, resulting in an overall increase in photocurrent. We performed a comparative study of the effects of the electrolytes with PVDF (which we name P1) and without PVDF (which we name M1) in cobalt-based electrolytes in 3-methoxy propionitrile solvent in DSCs. 1 Electrolytes containing the PVDF polymer exhibit excellent stability, which is attributed to the strong electron-withdrawing functional group-CF 2. We prepared cobalt-based electrolyte impregnated with PVDF, and we made thin titanium dioxide (TiO 2) mesoporous films on fluorine-doped tin oxide conducting glass for these electrolytes. We prepared the counter electrode and DSCs by
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