Low-temperature oxygen plasma treatment of TiO2 film for enhanced performance of dye-sensitized solar cells

The effects of low-temperature O2 plasma treatment of a TiO2 film are studied with the objective of improving the performance of dye-sensitized solar cells (DSSCs). X-ray photoelectron spectra (XPS) reveal that the ratio of titanium dioxide to titanium sub-oxides is increased in the O2 plasma-treated TiO2 film, compared with that of the untreated TiO2 film. This increase suggests that the oxygen vacancies in the film are effectively reduced. The near-edge X-ray absorption fine structure (NEXAFS) spectra results agree with the XPS result. It is proposed that there is a correlation between the shifts of the peaks in the NEXAFS spectra and the adsorption of N719 dye on the TiO2 particles. A DSSC having an O2 plasma-treated, 4 μm thick TiO2 film electrode renders a short-circuit photocurrent of 7.59 mA cm−2, compared with 6.53 mA cm−2 for a reference cell with an untreated TiO2 electrode of the same thickness. As a result of these changes, the solar-to-electricity conversion efficiency of the O2 plasma-treated cell is found to be 4.0% as compared with 3.5% for the untreated cell. This improvement in the performance is rationalized on the basis of increased N719 dye adsorption on to the TiO2, due to the reduction in the number of oxygen vacancies caused by the oxygen plasma treatment.