Direct measurement of the recombination losses via the transparent conductive substrate in dye sensitized solar cells

The role of the conducting glass substrate (fluorine doped tin oxide, FTO) on the performance of dye sensitized solar cells was investigated using a new technique. In most techniques used today it is impossible to isolate the source of the recombination process. This process can occur simultaneously via the nanocrystalline TiO₂ particles and via the conductive glass that are in contact with the redox electrolyte. The new technique enabled us to measure the photovoltaic performance losses of the solar cell, only via the conducting glass under stationary and working conditions at different light intensities and electrolyte concentrations. The principal idea of this new technique was to change systematically the ratio between the areas of the particle matrix and the conductive glass that are in contact with the electrolyte. The method involved gradual increment of the glass area and thereby enabled extraction of the influence of the conducting glass only. The results obtained show that, under standard cell working conditions, the losses emerging from the conducting glass to the DSSC performance are relatively minimal and occur mainly near the cell's maximum power point. These results suggest that at least in the case of cells that operate with I^-/I₃^- redox liquid electrolyte the contribution of thin underlayers covering the conductive substrate is small.