On the effect of Al2O3 blocking layer on the performance of dye solar cells with cobalt based electrolytes

Dye solar cells with Co-(III)/Co-(II) redox mediators have been prepared. To obtain higher conversion efficiencies, the recombination between photoinjected electrons and Co-(III) species was minimized by deposition of a thin Al2O3 blocking layer over the mesoporous TiO2 surface. Measurements of current-voltage characteristic curves, both under illumination and in dark conditions, together with electrochemical impedance spectroscopy demonstrate the great effectiveness of the addition of a blocking layer in cells containing cobalt based electrolyte, by substantially reducing the recombination current. The consequent power conversion efficiency increase is more than double, passing from 0.94% to 2.48% under 300 W m(-2) AM 1.5 illumination.