Function of Tetrabutylammonium on High-Efficiency Ruthenium Sensitizers for Both Outdoor and Indoor DSC Application.

The function of tetrabutyl ammonium ions (TBA) in a sensitizer used in dye-sensitized solar cells (DSC) is contradictory. TBA can reduce unwanted charge-recombination by protecting the TiO surface and reduce dye aggregation, enhancing the photovoltaic performance. It will also compete with the dye-loading on the TiO film, decreasing the short-circuit current density of the cell. Three ruthenium sensitizers (DYE III, DUY11, and DUY12 containing two H, one H/one TBA, and two TBA, respectively) were prepared to systematically investigate the function of TBA in a dye for DSC under both standard sunlight and indoor illumination. The optical properties and frontier orbital energy level of the sensitizers are not influenced significantly by the number of TBA. Under the standard 1 sun illumination, DSCs based on DUY11 (containing one H and one TBA) achieved the highest power conversion efficiency (PCE) of 11.47%. Overall, optimized DSCs sensitized by the three ruthenium dyes all have the PCE over 10%, which is higher than that (9.95%) of N719-dyed cell fabricated at the same conditions. Under the illumination of a light emitting diode (LED), DSCs sensitized by DUY11 also have the highest efficiency of 19%. Furthermore, DUY12 with two TBA exhibits superior photovoltaic performance compared to a DYE III (containing two H in the anchoring ligands)-dyed cell; although these two dyes have similar photovoltaic performance under standard 1 sun lighting. The important function of TBA in reducing the charge recombination (by protecting TiO surface and avoiding dye aggregation) of a DSC under indoor lighting (when small number of electrons were excited by weak light) is also revealed.