Tandems of solid dye-sensitized solar cell with carbon nanotubes interlayer

The light-to-electron conversion efficiency of the dye-sensitized solar cell (DSC) was recently improved up to 11.1{\%}. However, this efficiency is not sufficient for cost-effective commercial production, so the expansion of the absorption region of the solar cell is needed. For transparent carbon nanotubes, parallel-connected tandem DSCs is developed. Novel parallel type of tandem cell structure is created. We create a parallel combination for cells using different dyes. The top cell is transparent and the bottom cell only uses light passing through the top cell. Instead of a common platinum counter electrode as interlayer, we use transparent carbon nanotubes (CNTs) coated on hole transport layers of each sub-cell, as an interlayer counter electrode. With high enough conductivity and high optical transparency, the compatibility of CNTs work as the interlayer counter electrode performing even better than Pt. The short-circuit current density (Jsc) for the tandem cell is demonstrated to be higher than that of separate the front and back photo electrodes.A model using light energy absorbed by the photo electrode is N719 top cell and a black-dye bottom cell is developed. Now the prototype of DSC tandem cell has been proved with the efficiency of 0.293{\%} with 0.2 cm$^{2}$ area.