New LbL-TiO2/ZnO Compact Films to Improve Performance of Dye-Sensitized Solar Cells

The preparation of nanostructured thin films consisted of TiO2/ZnO bilayers (BL) and their application in dye-sensitized solar cells (DSCs) are reported. The film was prepared by the Layer-by-Layer (LbL) technique using, respectively, acid and basic sols of TiO2 and ZnO nanoparticles. The particles in the sols were characterized by dynamic light scattering (DLS) and the compact morphology of the LbL films were probed by scanning electronic (SEM) and atomic force (AFM) microscopies. The photoelectrochemical parameters of DSCs with 0, 15 and 20 BL were assessed by current-voltage (JxV) curves, incident photon-to-current efficiency (IPCE), electron lifetime and electrochemical impedance spectroscopy (EIS). These results revealed a significant improvement (up to 67%) on the DSC conversion efficiency promoted by LbL film underlayers, with enhancements ascribed to an efficient blocking effect preventing the FTO/I-3(-) charge recombination and improved contact between the mesoporous-TiO2 and the conducting substrate (FTO).