Wet Imprinting of Channel‐Type Superstructures in Nanostructured Titania Thin Films at Low Temperatures for Hybrid Solar Cells

Hierarchically structured titania films, exhibiting interconnected foam‐like nanostructures and large‐scale channel‐type superstructures, were achieved in an energy‐saving way at low temperatures by a polymer template‐assisted sol–gel synthesis in combination with a wet‐imprinting process. The surface morphology was probed with scanning electron microscopy and atomic force microscopy, whereas the inner morphology was characterized with grazing incidence small‐angle X‐ray scattering measurements. Compared to the initial hybrid films, the titania films showed reduced structure sizes caused by removal of the polymer template. UV/Vis measurements showed an additional light‐scattering effect at various angles of light incidence in the hierarchically structured titania films, which resulted in higher light absorption in the wet‐imprinted active layer. To give proof of viability, the titania films were evaluated as photoanodes for dye‐free hybrid solar cells. The dye‐free layout allowed for low‐cost fabrication, avoided problems related to dye bleaching, and was a more environmentally friendly alternative to using dyes. Under different angles of light incidence, the enhancement in the short‐circuit current density was in good agreement with the improvement in light absorption in the superstructured active layer, demonstrating a positive impact of the superstructures on the photovoltaic performance of hybrid solar cells.