Investigations on the influence of surfactant in morphology and optical properties of zinc oxide nanopowders for dye-sensitized solar cells applications

We studied the influence of the synthesis route on the morphology and optical properties of zinc oxide (ZnO), with applications in dye-sensitized solar cells (DSSCs). For this purpose, we obtained surfactant capped ZnO nanopowders, in the presence of non-ionic surfactants with different structures, and demonstrated their behavior as semiconductors in DSSCs. The ZnO nanopowders and films (obtained from nanopowders using the doctor blading method) were analyzed by transmission electron microscopy (TEM), high resolution TEM (HRTEM), and selected area electron diffraction (SAED). The optical properties were examined by UV, visible spectroscopy, and the band gap energies were calculated using the Tauc equation. The values obtained for DSSCs efficiencies were in good agreement with the characteristics of ZnO, both powders and films, and can be correlated with the synthesis route. The highest efficiency (1.19%) was achieved using ZnO nanopowder capped with Triton X-100, having a mean diameter of ～19 nm. We find that the use of capped ZnO nanoparticles is favorable for DSSCs, possibly because of the good porosity of the film and better dye adsorption. Moreover, the efficiency of the cells is influenced by the surfactant structure, due to the particle morphology.