A strategy to stabilise the local structure of Ti4+ and Zn2+ species against aging in TiO2/aluminium-doped ZnO bi-layers for applications in hybrid solar cells

We explore a strategy to counteract aging issues in TiO2/aluminium-doped ZnO bi-layers used in hybrid solar cells photo-anodes, mainly related to Zn diffusion in the TiO2 matrix. Different Ti4+ and Zn2+ local structures within the anatase grains and along the film thickness were found as a function of post-deposition annealing treatments in the range between 200 degrees C and 500 degrees C by synchrotron radiation extended x-ray absorption fine structure analyses. In particular, in the 500 degrees C-treated sample, diffusion of zinc species along the TiO2 grain-boundaries has been observed with aging (3 years). In contrast, a mild thermal budget at 200 degrees C favours a proper atomic arrangement of the zinc-containing anatase lattice which reduces Zn diffusion, thus guaranteeing a good stability with aging. (C) 2014 AIP Publishing LLC.