Synthesis of a novel amphiphilic polymeric ionic liquid and its application in quasi-solid-state dye-sensitized solar cells

A novel polymeric ionic liquid (PIL), poly(oxyethylene)-imide-imidazole complex coupled with iodide anions (coded as POEI-II), was synthesized for preparing the gel electrolyte for quasi-solid-state dye-sensitized solar cells (QSS-DSSCs). Herein, POEI-II, which acts simultaneously as a redox mediator in the electrolyte and a polymer for the gelation of an organic solvent-based electrolyte, was used to improve cell durability. In the structure of POEI-II, the presence of the POE segment can chelate lithium cations (Li⁺) within the electrolyte to improve the open-circuit voltage (V_OC) of a QSS-DSSC, and enable a strong dipole-dipole lone-pair electron interaction with iodide ions (I^-) of electrolyte composition rendering the high ionic conductivity and the diffusivity of a redox couple within the gel electrolyte. Consequently, the QSS-DSSC with the POEI-II gel electrolyte reaches a high cell efficiency of 7.19%. In addition, 5 wt% of multi-wall carbon nanotubes (MWCNTs) are incorporated into the POEI-II gel electrolyte as the extended electron transfer material (EETM) to facilitate charge transfer from the counter electrode to the redox mediator, which benefits the dye regeneration more efficiently. Meanwhile, the POE segments in POEI-II can prevent the MWCNTs from aggregation, which makes the well dispersed MWCNTs largely exposed to redox mediators. The highest cell efficiency of 7.65% was achieved by using the POEI-II/MWCNT gel electrolyte and it showed an unfailing durability of greater than 1000 h under 50°C. This properly designed PIL paves a promising way for developing highly efficient and durable QSS-DSSCs.