Influence of alkyl dihalide gelators on solidification of dye-sensitized solar cells

Quasi-dye-sensitized solar cells were prepared by using ionic liquid-type electrolytes and gelators consisting of polyvinylpyridine and alkyl dihalides. Gelation occurred by the reaction of polyvinylpyridine and alkyl dihalides. When the chain length of the dihalides was varied, the short-circuit current (Jsc) increased with an increase in the chain length. However, the open-circuit voltage (Voc) and fill factor (ff) slightly decreased. The increase in Jsc was brought about by the decrease in the interfacial resistances between the gel electrolyte and the counter electrode. In addition, the increase in the Jsc was explained by increases in the apparent diffusion coefficient of I−/I3− when the chain length increased. Decreases in Voc and ff were explained by back-electron transfers from TiO2 to iodine in the electrolytes. Voc of the cells solidified by alkyldiiodide was lower than that solidified by alkyldichloride or alkyldibromide. It was explained by negatively shifted redox potential of I−/I3−, compared with those for Cl−/Cl2 or Br−/Br2.