Layer-by-layer self assembly deposition and characterization of TiO2 nanoparticles by using a short chain polycation

Using low molecular weight polyethylenimine (PEI), transparent thin films of TiO2 nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO2 and PEI after each dip cycle. The adsorption of both TiO2 and PEI showed a saturation dip time of 10 min. The effect of dip time on the growth mode and surface morphology was investigated by scanning electron microscopy (SEM) and non-contact atomic force microscopy (AFM). It was found that growth proceeds in the form of laterally broad islands in case of short dip times, and taller but laterally smaller islands in case of longer dip times. A model was proposed which describes the role of dip time on the lateral growth of TiO2 islands. Low molecular weight PEI resulted in around 25% less adsorption of PEI and TiO2 in comparison with high molecular weight PEI, but because of lower remaining ash, could be promising for dye-sensitized solar cell photoelectrode applications, in which removal of polyelectrolyte after the formation of thin film enhances the electrical properties and therefore the efficiency of solar cell.