Protic ionic-liquid modifies the microstructure and photoelectrochemical performance of zinc oxide-based photoanodes

Abstract

Zinc oxide (ZnO) nanoparticle suspensions were synthesized through a hydrothermal process with the addition of 3-triethylammonium-propanesulphonic acid tetrafluoroborate (TEA-PS·BF4) ionic liquid (IL). Thin films prepared with the resulting suspensions were used as photoanodes for dye-sensitized solar cells (DSSCs). Rietveld refinement of X-ray diffraction patterns showed that the IL influences the anisotropy of crystallite shape, as confirmed by Raman spectroscopy, and microstrain decreases with the IL concentration. Interestingly, the IL modified the ZnO nanoparticle morphology and the average size of the pores of the film. The electrochemical characterization of DSSCs revealed improved photoanode performance with 5 wt% IL (2.23% efficiency and 7.13 mA·cm–2 current density) compared with the film without IL (1.93% efficiency and 4.11 mA·cm–2 current density). Electrochemical impedance spectroscopy showed that samples with IL exhibited increased resistance to charge transfer at ZnO/electrolyte interface responsible for the observed increased energy conversion.