Rapid fabrication of inverse opal TiO2 for application in dye-sensitized solar cell

Abstract

Herein a rapid fabrication method of inverse opal (IO) TiO2 is presented. By using doctorblade technique, an ordered IO TiO2 can be obtained from a slurry of monodispersed polystyrene (PS) colloids and titanium precursor, followed by calcination of PS spheres. This method saves a lot of valuable time and effort compared to the convectional self-assembly technique of PS spheres which takes up 2 days just to obtain opal-like templating film on a substrate. This simple and time-saving method could be very useful in the application in large

scale production of dye-sensitized solar cells (DSSCs). In this report, DSSCs were fabricated with bilayer of mesoporous nanocrystalline TiO2 (nc-TiO2) and IO TiO2 on fluorinated tin oxide (FTO) glass using the rapid fabrication method. A quantitative comparison of the power conversion efficiency (PCE), incident photon-to-current conversion efficiency (IPCE)and short circuit current densities (JSC) was performed on the bilayer DSSCs and reference

DSSCs with only one layer of nc-TiO2. An improvement in PCE was seen in bilayer cells

compared to reference cells of the same thickness. The enhancement in IPCE across the

visible spectrum suggests light scattering in the IO TiO2 layer was the beneficial factor. In addition, there was also an increase in JSC. The optimum thickness of the bilayer film was found to be around 15.5 um, where the additional of the IO TiO2 layer lead to increased PCE from 2.8% to 3.5%. The explanation of why the efficiency curve goes through a maximum is

that with increasing thickness, the presence of more TiO2 particles contribute to the

photogeneration of conduction band electrons, thus efficiency increases. However, as the film becomes too thick, the existence of too many grain boundaries or trap states causes even more electron-hole recombination, lowering the photovoltaic performance of the solar cell.