Effect of alkyl chain length of imidazolium cations on the electron transport and recombination kinetics in ionic gel electrolytes based quasi-solid-state dye-sensitized solar cells

A series of stable quasi-solid-state dye-sensitized solar cells (QS-DSSCs) are prepared by the 12-hydroxystearicacid as low molecular mass organogelator (LMOG) to gelate the ionic liquid with different alkyl chain lengths (3, 4, and 7). The influence of alkyl chain length of imidazolium cations (Im(+)) on the kinetic processes of electron transport and recombination are investigated by Electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent spectroscopy/intensity-modulated photovoltage spectroscopy (IMPS/IMVS). It is found that the ionic gel electrolytes (IGEs) with different alkyl chain lengths of Im(+) can influence the competitive adsorption effects of imidazolium cations (Im(+)) and Li+, and further affect the charge diffusion, the electron recombination/transport processes, the shift of TiO2 conduction band edge and surface states distribution. The IGE with longer alkyl chain length of Im(+) can prolong the electron recombination lifetime, promote the incidental photon-to-electron conversion efficiency (IPCE) and the short circuit photocurrent density (J(sc)). An excellent QS-DSSC based on the IGE with the longer alkyl chain of Im(+) gives the highest photoelectric conversion efficiency. Moreover, all the QS-DSSCs based on IGEs exhibit excellent durability without losing their photovoltaic performances during the accelerated thermal and light-soaking test. These results are very important to the researches on the electrochemical mechanism and application of QS-DSSCs based on IGEs. (C) 2015 Elsevier Ltd. All rights reserved.