A Low Temperature Route toward Hierarchically Structured Titania Films for Thin Hybrid Solar Cells

The requirement of high-temperature calcination for titanium dioxide in (solid-state) dye-sensitized solar cells (DSSCs) implies challenges with respect to reduced energy consumption and the potential for flexible photovoltaic devices. Moreover, the use of dye molecules increases production costs and leads to problems related with dye bleaching. Therefore, fabrication of dye-free hybrid solar cells at low temperature is a promising alternative for current DSSC technology. In this work the authors fabricate hierarchically structured titania thin films by combining a polystyrene-block-polyethylene oxide template assisted sol-gel synthesis with nano-imprint lithography at low temperatures. The achieved films are filled with poly(3-hexylthiophene) to form the active layer of hybrid solar cells. The surface morphology is probed via scanning electron microscopy and atomic force microscopy, and the bulk film morphology is examined with grazing incidence X-ray scattering. Good light absorption by the active layer is proven by UV-vis spectroscopy. An enhancement in light absorption is observed and ascribed to light scattering in mesoporous titania films with imprinted superstructures. Accordingly a better photovoltaic performance is found for nano-imprinted solar cells at various angles of light incidence.