Spontaneous solar water splitting by DSSC/CIGS tandem solar cells

A tandem solar cell equipped with a dye-sensitized solar cell (DSSC) and a CuInxGa1−xSySe1−y (CIGS) bottom sub-cell was assessed for photovoltaic cell (PV)-assisted water splitting application. Two types of cobalt complexes ([Co(bpy)3]2+/3+ and [Co(phen)3]2+/3+) were tested as the redox couples in the DSSC sub-cell. Of these, [Co(phen)3]2+/3+ showed a larger open circuit potential and higher power conversion efficiency for the DSSC/CIGS tandem cell with high stability due to its more positive redox potential. Two unit cells of the DSSC/CIGS tandem cell were assembled as a module to supply sufficient power for water electrolysis. Spontaneous solar water splitting was realized when the DSSC/CIGS module was connected to a stainless steel anode and a platinum cathode. The [Co(phen)3]2+/3+ redox couple in the tandem cell was found to have high solar to hydrogen conversion efficiency (ηSTH = 4.65%) in the PV-assisted electrolysis cell.