Dye-Sensitized Tandem Solar Cells with Extremely High Open-Circuit Voltage Using Co(II)/Co(III) Electrolyte

For achieving a high open-circuit voltage (Voc) in dye-sensitized tandem solar cells, series-connected tandem solar cells were fabricated. In order to optimize series-connected tandem solar cell systems, the current density of the top and bottom cells should be well matched to be identical, and the Voc of each of the cells should also be as high as possible. Furthermore, the top cell should be transparent and the bottom cell should have the longer-wavelength absorption, for utilizing only the light passing through the top cell. This leads to a high Voc. In this study, we report dye-sensitized tandem solar cells having an extremely high Voc using the Co(bpy)32+/3+ (bpy=2,2′-bipyridine) redox couple. Dye-sensitized tandem solar cells employing JK303/HC-A1 with the Co(bpy)32+/3+ redox couple as the top cell and N749/HC-A4 with the I−/I3− redox couple as the bottom cell were shown to have an extremely high Voc of >1.66 V, the highest value for dye-sensitized tandem solar cells reported to date.