Hybrid electrolytes prepared from ionic liquid-grafted alumina for high-efficiency quasi-solid-state dye-sensitized solar cells

Abstract

Alumina (Al₂O₃) nanoparticles were covalently surface-modified with an ionic liquid (IL) to improve their miscibility with ILs such as 1-methyl-3-propylimidazolium iodide (MPII). Hybrids consisting of MPII and the surface-modified IL-Al₂O₃ nanoparticles were utilized as an I₂-free electrolyte for quasi-solid-state dye-sensitized solar cells (DSSCs). The synthesis and properties of the IL-Al₂O₃ nanoparticles and hybrid electrolytes were characterized by Fourier transform infrared (FT-IR) spectroscopy, UV-visible spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The viscosity of the electrolyte continuously increased with the content of IL-Al₂O₃, and the fluidity almost disappeared completely when the MPII:IL-Al₂O₃ weight ratio was 95 : 5 or 90 : 10. The energy conversion efficiencies of DSSCs fabricated with IL-Al₂O₃ were always greater than those with pristine Al₂O₃. Such a finding is due to the favorable interactions and good miscibility between MPII and IL-Al₂O₃, which in turn results in the formation of an interconnected channel pathway for ion transport. Incident photon-to-electron conversion efficiency (IPCE), intensity modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS) measurements were used to investigate the interfacial properties and electron transport characteristics. Upon utilizing double-layer structures with mesoporous TiO₂ beads, the efficiency increased to 7.6% at 100 mW cm⁻², one of the highest values reported for quasi-solid-state DSSCs.