The anti-recombination property and the surface area of TiO2 influence the efficiency of dye-sensitized solar cells (DSSCs). The effects of various over-layers and O-2 plasma treatment on TiO2 electrodes have been investigated. Over-layers were coated by dip coating in a solution of saturated Ba(NO3)(2), Mg(NO3)(2) and N2O6Sr, which reduced the recombination of electrons from the photo excited state of Ru dye. O-2 plasma treatment was applied to improve both the contact ability with the dye and the electron takeover capability by reducing oxygen vacancies on both the TiO2 and the over-layer surface. The photo conversion efficiency of DSSC was improved by both over-layer coating and O-2 plasma treatment. In particular, dipping in saturated Ba(NO3)(2) solution and O-2 plasma treatment (BP), the photo conversion efficiency was greatly improved from 5.27% to 6.76%. The reason was that the over-layers and O-2 plasma treatment decreased electron recombination. The energy barrier of the modified over-layers blocks the electron transfer from TiO2 to the electrolyte, and consequently increases electron density by extending the electron lifetime. O-2 plasma treatment also increased the Ru dye absorption. (c) 2010 Elsevier B.V. All rights reserved.