Impact of Catalytic Additive on Spray Deposited and Nanoporous Titania Thin Films Observed via in Situ X-ray Scattering: Implications for Enhanced Photovoltaics

With the aim of obtaining nanostructured titania thin films for the potential use in hybrid or dye sensitized solar cells, the amphiphilic diblock copolymer polystyrene-b-poly(ethylene oxide) is employed as a structure directing template in combination with sol-gel chemistry. For easy upscaling, spraying is used as a deposition technique. In situ grazing incidence small-angle X-ray scattering (GISAXS) measurements are performed during spraying and show that most titania structures are already formed within the solution prior to deposition. However, structural rearrangement is enabled during the deposition period when small amounts of hydrochloric acid (HCl) are used as a catalytic additive to the spray solution. This behavior is ascribed to an altering of the reaction dynamics and phase separation in the presence of HCl, which significantly improves the templating effect of the employed diblock copolymer. With HCl as an additive the final nanoscale morphologies exhibit smaller pore sizes and strongly enhanced order as compared to thin films sprayed from solutions that do not contain HCl as quantified with atomic force microscopy, scanning electron microscopy, and GISAXS.