TiO2 compact layers prepared by low temperature colloidal synthesis and deposition for high performance dye-sensitized solar cells

Compact layers are used in dye-sensitized solar cells (DSSCs) to passivate transparent conducting oxides (TCOs). TCO passivation increases DSSC performance by reducing electrical loss from recombination at the TCO-electrolyte interface and by improving electrical contact between the TCO and TiO2 photoelectrode. A novel process for synthesis of 4.5 nm colloidal TiO2 compact layer particles via acid hydrolysis of titanium isopropoxide was developed. DSSCs fabricated with the colloidal TiO2 compact layer, with no compact layer, and those with an RF-sputtered compact layer were evaluated. Relative to a DSSC with no compact layer, the colloidal compact layer improved the short-circuit current density, fill factor, and solar energy conversion efficiency by 17.6%, 4.4%, and 25.3%, respectively. Relative to the sputtered compact layer, the colloidal compact layer improved the short-circuit current density and solar energy conversion efficiency by 5.5% and 5.3%, respectively, with no significant change in the fill factor. The improved DSSC characteristics were attributed to increased shunt resistance due to decreased electrolyte reduction at the TCO-electrolyte interface and decreased series resistance due to improved electrical contact between the TCO and the TiO2 photoelectrode.