Atomic layer deposition of anatase TiO2 on porous electrodes for dye-sensitized solar cells

Abstract

Thin TiO2 films were grown by atomic layer deposition on planar and porous substrates and characterized by Raman spectroscopy, x-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry. The growth conditions of anatase TiO2 are investigated, motivated by the application in dye-sensitized solar cells, where best results are achieved with electrodes based on anatase TiO2. To enforce an anatase TiO2 growth on substrates stimulating rutile growth, a symmetry breaking ultra thin buffer layer of five cycles Al2O3 was introduced. With this buffer layer anatase TiO2 deposition was demonstrated on planar rutile TiO2 substrates. However, it was found that the necessity of the buffer layer depends on the substrate structure. On porous TiO2 electrodes containing a mixture of anatase and rutile TiO2 domains, a direct anatase TiO2 growth was possible even without a buffer layer.