Modification of TiO₂ Electrode with Organic Silane Interposed Layer for High-Performance of Dye-Sensitized Solar Cells

Back electron transfer from the TiO₂ electrode surface to the electrolyte is the main reason behind the low-open circuit potential (<i>V</i>_oc) and the low-fill factor (FF) of the dye-sensitized solar cells (DSSCs). Modifications to the TiO₂ electrode, fabricated using {010}-faceted TiO₂ nanoparticles with six different kinds of silane, are reported to decrease the back electron transfer on the TiO₂ surface. The effect of alkyl chain length of hydrocarbon silanes and fluorocarbon silanes on adsorption parameters of surface coverage and adsorption constant, interfacial resistance, and photovoltaic performances were investigated. Adsorption isotherms, impedance analysis, and photovoltaic measurements were used as the investigation techniques. The reduction of back electron transfer depended on the TiO₂ surface coverage by silane, alkyl chain length, and the molecular structure of the silane. Even though <i>V</i>_oc and FF were improved, significant reduction in short-circuit photocurrent density (<i>J</i>_sc) was observed after silanization because of desorption of dye during silanization. A new approach, sequential adsorption process of silane and dye, was introduced to enhance <i>V</i>_oc and FF without lowering <i>J</i>_sc. Heptadecafluorodecyl trimethoxy-silane showed the highest coverage on the surface of the TiO₂ and had the highest effect on the performance improvement of the DSSC, where <i>V</i>_oc, FF, and efficiency (η) were improved by 22, 8.0, and 22%, respectively