Highly efficient dye-sensitized solar cells based on low concentration organic thiolate/disulfide redox couples

An imidazolium thiopropionate-based redox couple is introduced as an improved organic alternative to iodide/triiodide (I-/I3-) couples for dye-sensitized solar cells (DSSCs). The synthesized thiolate/disulfide (BMIT/BMIDT) redox couple shows negligible absorption in the visible spectral range, and higher redox potential (+0.72 V vs. NHE) compared with that of I-/I3-. With the optimized redox couple (such as 0.1 M/0.1 M)/dye N719 formulation, the fabricated DSSCs exhibit an average overall power conversion efficiency (PCE) of 6.8% and 8.1% under the simulated air mass 1.5 solar spectrum illumination at 100 and 50 mW cm-2, respectively. However, a higher concentration of the BMIT/BMIDT redox couple (such as 0.4 M/0.4 M) decreases the PCE of the devices, due to the desorption of dye molecules from the TiO2photoelectrode surface.