Low-Temperature Fabrication of Mesoporous Titania Thin Films
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MRS Advances © 2017 Materials Research Society DOI: 10.1557/adv.2017.406
Low-Temperature Fabrication of Mesoporous Titania Thin Films Lin Song1, Volker Körstgens1, David Magerl1, Bo Su1, Thomas Fröschl2, Nicola Hüsing2, Sigrid Bernstorff3 and Peter Müller-Buschbaum1 1
Technische Universität München, Physik-Department, Lehrstuhl für Funktionelle Materialien, James-Franck-Str. 1, 85748 Garching, Germany. 2 Materialchemie, Chemie und Physik der Materialien, Universität Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria. 3 Elettra - Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163,5 in AREA Science Park Basovizza, 34149 Trieste, Italy. ABSTRACT Mesoporous titania films are prepared via the polymer-template assisted sol-gel synthesis at low temperatures, using the titania precursor ethylene glycol-modified titanate (EGMT) and the diblock copolymer polystyrene-block-polyethyleneoxide (PS-b-PEO). UV-irradiation is chosen as a low temperature technique to remove the polymer template and thereby to obtain titania sponge-like nanostructures at processing temperatures below 100 °C. After different UV irradiation times, ranging for 0 h to 24 h, the surface and inner morphologies of the titania films are studied with scanning electron microscopy (SEM) and grazing incidence small-angle x-ray scattering (GISAXS), respectively. The evolution of the band gap energies is investigated using ultraviolet/visible (UV/Vis) spectroscopy. The findings reveal that 12 h UV-treatment is sufficient to remove the polymer template from the titania/PS-b-PEO composite films with a thickness of 80 nm, and the determined bad gap energies indicate an incomplete crystallization of the titania nanostructures. INTRODUCTION Nanostructured titania thin films have received great attention in different fields of applications such as photovoltaics, photocatalysis, and gas sensing [1-8]. The main advantages are related to their chemical and optical stability, non-toxicity, low cost and controllable morphology [9-14]. For example, titania, especially its anatase polymorph, has been widely used in the field of dyesensitized solar cell (DSSCs) [15-19]. For such solar cell applications, a high surface area is favorable for the film morphology, which has a great influence on the light absorbance and the recombination probabilities of the photo-generated electrons and holes [20-23]. Therefore, sponge-like titania nanostructures appear particularly promising because of their morphology featuring a high surface-to-volume ratio and an interconnected network [24-26]. The high surface-to-volume ratio enables a high dye loading and thereby high sunlight absorption. The interconnected network structure is beneficial for charge transport, since regions with defects causing a higher resistance can be bypassed by the charge carriers. In literature, a high power conversion efficiency (PCE) of 12.3 % was reported in DSSCs which used mesoporous titania films as photoanodes [2]. Also when replacing the liquid electrolyte with a solid hole conductor
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