Stable Quasi-Solid-State Dye-Sensitized Solar Cells Using Novel Low Molecular Mass Organogelators and Room-Temperature Molten Salts
Stable quasi-solid-state dye-sensitized solar cells (DSCs) were fabricated by using room-temperature molten salts (1-methyl-3-hexyl-imidazolium iodide), and a series of diamine derivatives with different lengths of alkyl chain as low molecular mass organogelators (LMOGs). The number of methylene (-CH2-) units between the two amide carbonyl groups in the gelator molecule has significant influence on the charge transport property of gel electrolyte, and the kinetic processes of the electron transport and recombination. Less compact networks of the ionic liquid gel electrolytes containing odd-numbered -CH2- gelator facilitate the diffusion of I-3(-) and I-. Also, the odd-numbered -CH2- gelators-based DSCs exhibit longer electron recombination lifetime and a higher open circuit potential (V-oc) compared with the DSCs based on even-numbered -CH2- gelators; consequently, the photovoltaic performances of DSCs based on odd-numbered -CH2- gelators are much better than those even-numbered -CH2- gelators. Remarkably, the results of the accelerated aging tests showed that the ionic liquid gel electrolyte-based DSCs could retain 93%-99% of their initial photoelectric conversion efficiencies (eta) under heat at 60 degrees C, and 100% of their initial photoelectric conversion efficiencies under one sun light soaking with UV cutoff filter at 50 degrees C for 1000 h. This excellent long-term stability of quasi-solid-state DSCs is very important for application and commercialization of DSCs.