Tandem dye-sensitized solar cells with a back-contact bottom electrode without a transparent conductive oxide layer

We report on the architecture of tandem dye-sensitized solar cells (DSSCs) with a back-contact bottom electrode without a transparent conductive oxide layer (TCO-less tandem DSSCs). The bottom electrode consists of glass/stained porous TiO2/back-contact porous metal. As the structure has fewer TCO layers than simple mechanical stack tandem DSSCs, more light reaches the bottom electrode. Two model dyes (D131 and N719) were used to confirm the tandem performance of the cells. The open-circuit voltage (V-oc) was the sum of the V-oc of the top cell and the V-oc of the TCO-less bottom cell, showing that the cell worked as a tandem cell. The power conversion efficiency of the TCO-less tandem DSSC (7.10%) was greater than that of the stack tandem DSSCs (6.28%).