The Function of a TiO2 Compact Layer in Dye-Sensitized Solar Cells Incorporating “Planar” Organic Dyes

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Abstract
We present a device based study into the operation of liquid electrolyte dye-sensitized solar cells (DSSC’s) using organic dyes. We find that, for these systems, it is entirely necessary to employ a compact TiO2 layer between the transparent fluorine doped SnO2 (FTO) anode and the electrolyte in order to reduce charge recombination losses. By incorporation of a compact layer, the device efficiency can be increased by over 160% under simulated full sun illumination and more than doubled at lower light intensities. This is strong evidence that the more widely employed ruthenium based sensitizers act as to “insulate” the anode against recombination losses and that many planar organic dyes employed in DSSC’s could greatly benefit from the use of a compact TiO2 blocking layer. This is in strong contrast to DSSC’s sensitized with ruthenium based systems, where the introduction of compact TiO2 has only marginal effects on conversion efficiencies.