For the EIS study, DSCs using commercial FTO/NiO electrodes were used, and we focused only on the solvents AN, PN and MPN, all of which have similar donor numbers (Table 1). The V OC is highest for VN and PN, but the main factor inuencing the overall DSC efficiency is J SC. discussed above, the efficiencies of DSCs sensitized with are signicantly inuenced by the choice of solvent in the electrolyte. Enhancement of DSC performance over time is a known phenomenon in n-type DSCs sensitized by some cop- per(I) 36 or ruthenium(II) dyes and appears to be associated with the formation of dye-aggregates which ultimately reorganize on the surface over periods of days. A ripening effect is also observed for the DSCs containing VN. This leads to an increase in h from 0.117% to 0.154 and 0.146% for the two DSCs aer 34 days, and this efficiency is essentially retained over the following 24 days. Pleasingly, the cells containing PN show enhanced performance upon ageing with a gain in J SC and no signicant change in V OC. One DSC containing AN aged badly with a drop in both J SC and V OC, leading to a reduction in photoconversion efficiency from 0.139 to 0.088%.
The ll-factors of all DSCs remain relatively high. Aer the initial assessment of their perfor- mances, the DSCs were stored under ambient conditions for a month and then their J-V characteristics were remeasured (Table 6 and Fig. the results discussed above favour AN as the elec- trolyte solvent, the long-term stability of the DSCs remains an important factor.