ZnO Nanostructures-based Dye-sensitized Solar Cells using TEMPO+/TEMPO Redox Mediator and Ruthenium(II) Complexes with 1,2,3-Triazole-derived Ligands
in: ChemPlusChem (2016)
A series of thiocyanate-free bis(tridentate) ruthenium(II) complexes incorporating 1,2,3-triazole-derived NNN-, NCN-, and CNC-coordinating ligands has been employed for sensitizing ZnO photoanodes for dye-sensitized solar cells (DSSCs). Additionally, the first use of the TEMPO+/TEMPO redox mediator as the surrogate of I3-/I- a redox couple in ZnO nanostructure-based DSSCs is presented. When compared to I3-/I--based electrolytes, shorter charge lifetimes and diffusion lengths were determined for the TEMPO+/TEMPO-based electrolyte. Nonetheless, similar power conversion efficiencies (PCEs) are achieved with both electrolytes for RuNCN and RuCNC, while higher PCEs are enabled by the iodine-free electrolyte in case of RuNNN. The combinations of the molecular sensitizers and the TEMPO-based electrolyte exhibit relatively high EQE and gain promising PCEs, ranging from 4.48 to 1.47%, which are – in part – comparable to that of ZnO-DSSCs with the benchmark N749 black dye. The TEMPO-based electrolyte also exhibits less absorption compared to its I3-/I- counterpart, a favorable feature to enhance light harvesting by the photoanode. Furthermore, the results show the effect of the dye sensitization procedure on PCE values: The use of ethanol as the solvent compared to methanol increases the DSSCs efficiency, which is attributed to an improved chemisorption of the sensitizer onto the ZnO surface