Phenothiazinedioxide-Conjugated Sensitizers and a Dual-TEMPO/Iodide Redox Mediator for Dye-Sensitized Solar Cells

Metal-free dyes containing a phenothiazinedioxide entity in the spacer were synthesized. The best conversion efficiency (7.47%) of the dye-sensitized solar cell (DSSC) by using new sensitizers with chenodeoxycholic acid as a co-adsorbent and the I-/I-3(-) electrolyte reached over 90% of that of the standard N719-based cell (8.10 %). A new type of ionic liquid containing the nitroxide radical (N-O-center dot) and iodide was successfully synthesized and applied to the DSSCs. If the I-/I-3(-) electrolyte was replaced with a dual redox electrolyte, that is, a TEMPO (2,2,6,6-tetramethylpiperidin- 1-oxyl) derivative with a dangling imidazolium iodide entity, the cell exhibited a high open-circuit voltage of 0.85 V and a cell efficiency of 8.36 %.