Cu(?/?) Complexes With Sulfur-Coordinated Ligands As Redox Mediators In Dye-Sensitized Solar Cells

Most of the copper redox couples reported in dye-sensitized solar cells?DSSC?were based on bipyridine or phenanthrolin ligands,so their coordinate atoms of central Cu^2+/+ion are nitrogens.Though there are many advantages of using copper redox couples in DSSCs,such as their easy-tuning redox potential,only a few kind of Cu redox couples have reached a high open-circuit voltage or photovoltaic performance.In this dsssertation,we focus on the investigation of new copper redox couples,which can be applied in DSSCs,aiming at improving the open-circuit voltage and overall photovoltaic performance by fine-tuning the coordination atoms of copper complexes.Natural systems have marvelously utilized copper complexes featured with sulfur-coordinating ligands.Copper complexes with sulfur-coordinating ligands have been attempted as redox mediators in dye-sensitized solar cells?DSSC?,the performance of which yet is not satisfied and still remains less well explored.Herein,we report new tetradentate copper complexes,[Cu?L1?]^2+/+?L1=1,2-bis??pyridin-2-ylmethyl?thio?ethane?and[Cu?L2?]^2+/+?L2=N,N'-dimethyl-N,N'-bis?pyridin-2-ylmethyl?ethane-1,2-diamine?.In contrast to[Cu?L2?]^2+/+,two of the coordinating atoms?on the structure of diamine?of[Cu?L1?]^2+/+were changed from N to S,resulting in a positive shift of its redox potential?610mV?.DSSCs based on[Cu?L1?]^2+/+achieved a high photovoltage of 0.96 V and power conversion efficiency?PCE?of 8.6%.For further confirmation and exploration of our new strategy,herein,we report the application of new copper complexes bearing a tetradentate polythioether ligand,[?S₄?Cu]^2+/+(1^2+/+,S₄=1,4,8,11-tetrathiocyclotetradecane),as a redox mediator in DSSC in comparison with its N₄-tetradentate counterpart[?N₄?Cu]^2+/+(2^2+/+,N₄=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane).Impressively,the changes of coordination atoms from N to S?both of four atoms?positively shift the formal redox potential of the copper complexes by600 mV,leading to a remarkably high photovoltage approaching 1.0 V.This is one of the highest photovoltage values reported thus far for DSSCs based on copper redox mediators.