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−/I3− electrolyte reached over 90 % of that of the standard N719-based cell (8.10 %). A new type of ionic liquid containing the nitroxide radical (NO.) and iodide was successfully synthesized and applied to the DSSCs. If the I−/I3− 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 %.