Dye-Sensitized Solar Cells with Efficiency over 36% under Ambient Light Achieved by Cosensitized Tandem Structure

The cosensitization process is an effective way to improve the performance of dye-sensitized solar cells (DSSCs), especially for tandem cells that employ the complementary light harvest ranges of different dyes. Herein, various cosensitized DSSCs are prepared using D35, XY1b, and Y123 dyes and employed to construct cobalt tandem DSSCs. First, the performance of single cells with and without scattering layers is studied. The results show that the cosensitized cells using D35 + XY1b and XY1b + Y123 dyes have higher power conversion efficiency (PCE) than the others, attributed to their longer light absorption wavelength and higher charge recombination resistance. Furthermore, the XY1b + Y123 cell has significantly higher open circuit voltage (V_oc) but slightly lower current density (J_sc) than those of the D35 + XY1b cell. The cosensitized systems are further utilized to prepare tandem cells. Photoelectrodes without and with scattering layers are used as top and bottom cells, respectively. It shows that by using D35 + XY1b (higher J_sc) and XY1b + Y123 (higher V_oc) as sensitizers of top and bottom cells, respectively, a PCE as high as 36.27% can be achieved under fluorescent lighting. The cells using these dyes have high long-term stability at room temperature.