Surface modification of TiO 2 electrode by various over-layer coatings and O 2 plasma treatment for dye sensitized solar cells

Abstract

The anti-recombination property and the surface area of TiO 2 influence the efficiency of dye-sensitized solar cells (DSSCs). The effects of various over-layers and O 2 plasma treatment on TiO 2 electrodes have been investigated. Over-layers were coated by dip coating in a solution of saturated Ba(NO 3) 2, Mg(NO 3) 2 and N 2O 6Sr, 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 TiO 2 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(NO 3) 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 TiO 2 to the electrolyte, and consequently increases electron density by extending the electron lifetime. O 2 plasma treatment also increased the Ru dye absorption.