High-voltage (1.8 V) tandem solar cell system using a GaAs/AlXGa(1-X)As graded solar cell and dye-sensitised solar cells with organic dyes having different absorption spectra

Stacked multijunction (tandem) solar cells have been prepared by mechanically stacking dye-sensitised solar cells (DSCs) and a GaAs/AlXGa(1-X)As graded solar cell (GGC) as the top and bottom cells, respectively. Three organic dyes with different absorption spectra (D131, D102 and D205) were used in the DSCs, in order to match the photocurrent density between the DSC and the GGC. Tuning the absorption range of the DSC by choosing an appropriate dye, increased the overall photovoltaic conversion efficiency due to the optimal utilisation of the solar spectrum in the individual cells. The open circuit photovoltages (V-OC) of the GGC and the DSC with D131 were 1.11 V and 0.76 V, respectively, resulting in a V-OC of 1.85 V and a photovoltaic conversion efficiency of 7.63% for the tandem cell. Although the overall conversion efficiency has not exceeded that of the GGC (7.66%), these tandem cells provide adequate V-OC values for water splitting applications. (C) 2011 Elsevier Ltd. All rights reserved.