Metal-containing Ionic Liquid-based Iodine-free Redox Couples For Dye-sensitized Solar Cells

Dye sensitized solar cell (DSSC) is composed of three parts (dye sensitized lightanode, counter electrode and electrolyte), the electrolyte plays an important role in the dyeregeneration and hole transportation. Traditional liquid electrolyte can realize highregeneration of dye and photo-electricity conversion efficiency of DSSCs, but organicsolvents are volatile, easy to leakage and limited long-term stability of DSSC. In addition,the commonly used (I-/I-3) redox couple have some limitations, such as the corrosion of themetal electrode and the absorption of visible light reduces the efficiency of the cell.In this work, we investigated gel electrolyte based on poly(ionic liquid) nanotubes anddevelopment of iodine-free metal-contained ionic liquid redox couples to replace I-/I-3redox couple. The main content is as follows:(1) Poly(divinybenzene-co-chloromethylstyrene)(poly(DVB-co-VBC)) nanotubes(NTs) and imidazolium surface functionalized NTs (Im-NTs) were synthesized by cationicpolymerization and utilized as the gelators for ionic liquid (IL) based quasi-solid-statedye-sensitized solar cells (DSSCs), without using any volatile organic solvents. Comparedwith synthesized pristine NTs, Im-NT based gel electrolytes showed higher ionicconductivity and diffusion coefficient. The fabricated DSSCs containing Im-NT based gelelectrolyte showed a power conversion efficiency of4.9%and5.5%under a simulated airmass1.5solar spectrum illumination at100mW cm-2and50mW cm-2, respectively. Thesuperior long-term stability of fabricated DSSCs indicated that solvent-free IL/Im-NT gelelectrolytes could overcome the drawbacks of cells containing volatile solvents.(2) An imidazolium-based Co-containing room temperature ionic liquid,bis(3-butyl-1-methylimidazolium) tetraisothiocyanato cobalt [BMI]2[Co(NCS)4], wassynthesized and characterized. The prepared[BMI]2[Co(NCS)4]/1-propyl-3-methylimidazoli-um iodine (PMII) hybrid redox couple showed higher redox potential as compared with that of iodide/triiodide (I-/I-3) redoxcouple. The resultant dye-sensitized solar cells (DSSCs) containing[BMI]2[Co(NCS)4]/PMII hybrid redox couple exhibited an average overall powerconversion efficiency of8.1%under the simulated air mass1.5solar spectrum illuminationat100mW cm-2, which are higher than that of traditional PMII/I2based electrolyteprobably due to the enhancement of Vocvalues of the hybrid electrolytes. Furthermore, thecell based on [BMI]2[Co(NCS)4]/PMII hybrid redox couple tested in this study showed aperformance enhancement (ca.10%) phenomenon after a120-day storage under ambientconditions.(3) A series of Cu complexes with ligand of ethanol amine (EA) and diethanol amine(DEA) were synthesized and cataloged as follows: Cu{NH2CH2CH2OH}6(PF6)2（1a），Cu{NH(CH2CH2OH)2}6(PF6)2（1b）, Cu{NH2CH2CH2OH}6(BF4)2（2a），Cu{NH(CH2CH2OH)2}6(BF4)2（2b）， Cu{NH2CH2CH2OH}6[(CF3SO2)2N]2（3a），Cu{NH(CH2CH2OH)2}6[(CF3SO2)2N]2（3b）. These above mentioned Cu complexes wereused as redox couples in the electrolyte. The fabricated DSSCs with3a and3b-basedelectrolyte achieved good efficiencies. When Z907was chosen as the dye,3a-basedelectrolyte showed the best performance with cell efficiency as high as1.91%under asimulated air mass1.5solar spectrum illumination at100mW cm-2. When D205waschosen as the dye,3b-based electrolyte showed the highest cell efficiency1.06%under asimulated air mass1.5solar spectrum illumination at100mW cm-2.