Electrolytes intensity-voltage measurements

Apart from recapture of the injected electrons by the oxidized dye, there are additional loss channels in dye-sensitized solar cells, which involve reduction of triiodide ions in the electrolyte, resulting in dark currents. The Ti02 layer is an interconnected network of nanoparticles with a porous structure. The functionalized dyes penetrate through the porous network and adsorb over Ti02 the surface. However, if the pore size is too small for the dye to penetrate, that part of the surface may still be exposed to the redox mediator whose size is smaller than the dye. Under these circumstances, the redox mediator can collect the injected electron from the Ti02 conduction band, resulting in a dark current (Equation (6)), which can be measured from intensity-modulated experiments and the dark current of the photovoltaic cell. Such dark currents reduce the maximum cell voltage obtainable, and thereby the total efficiency. 

Fig. 9. EIS of the DSSCs with (a) PMII/CB and BMII/CB electrolytes (b) pure IL electrolytes, measured at 100 mW cm-2 light intensity under open-circuit voltage (Lee et ah, 2010a).

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