Multifunctional Iodide-Free Polymeric Ionic Liquid for Quasi-Solid-State Dye-Sensitized Solar Cells with a High Open-Circuit Voltage

A polymeric ionic liquid, poly(oxyethylene)-imide-imidazolium selenocyanate (POEI-IS), was newly synthesized and used for a multifunctional gel electrolyte in a quasi-solid-state dye-sensitized solar cell (QSS-DSSC). POEI-IS has several functions: (a) acts as a gelling agent for the electrolyte of the DSSC, (b) possesses a redox mediator of SeCN-, which is aimed to form a SeCN-/(SeCN)(3)(-) redox couple-with a more positive redox potential than that of traditional I-/I-3(-), (c) chelates the potassium cations through the lone pair electrons of the oxygen atoms of its poly(oxyethylene)-imide-imidazolium (POEI-I) segments, and-(d) obstructs the recombination of photoinjected electrons with (SeCN)(3)(-) ions in the electrolyte through its POEI-I segments. Thus, the POEI-IS renders a high open-circuit voltage (V-OC) to the QSS-DSSC due to its functions of b-d and prolongs the stability of the cell due to its function of a. The QSS-DSSC with the gel electrolyte containing 30 wt % of the POEMS in liquid selenocyanate electrolyte exhibited a high Voc of 825.50 +/- 3.51 mV and a high power conversion efficiency (eta) of 8.18 +/- 0.02%. The QSS-DSSC with 30 wt % POEI-IS retained up to 95% of its initial ri after an at-rest stability test with the period of more than 1,000 h.