LiTFSI as a plastic salt in the quasi-solid state polymer electrolyte for dye-sensitized solar cells

Ionic conductivity and the type of ions are important for the composite polymer electrolyte (CPE) of the dye-sensitized solar cells (DSSCs). Lithium bis(trifluoromethane sulphone)imide (LiTFSI for short) which is easy to dissociate, is added in the composite polymer electrolyte(CPE) as a plasticizer. The LiTFSI acts differently from the conventional LiClO4. LiTFSI changes the conformation of the polymer chain and shows higher ionic conductivity than LiClO4. That contributes to the improvement of the short current density of the DSSC. Furthermore, the DSSCs with LiTFSI modification show higher photovoltage than the LiClO4. The anions of TFSI− prohibit the interface recombination more effectively compared with the LiClO4 as the electrochemical impedance spectroscopy indicated. With the LiTFSI modified electrolyte, the performances of the DSSCs under 1 Sun, AM1.5 are improved and reaches the highest of 4.82% at the LiTFSI:LiI = 0.116:1, much better than the original DSSC(3.6%) and the LiClO4 modified CPE electrolyte DSSC(4.32%).