Low‐Temperature Route to Crystalline Titania Network Structures in Thin Films

Abstract

A low temperature route to crystalline titania nanostructures in thin films is presented. The synthesis is performed by the combination of sol-gel processes, using a novel precursor for this kind of application, an ethylene glycol-modified titanate (EGMT), and the structure templating by micro-phase separation of a di-block copolymer. Different temperatures around 100 °C are investigated. The nanostructure morphology is examined with scanning electron microscopy, whereas the crystal structure and thin film compositions are examined by scattering methods. Optoelectronic measurements reveal the band-gap energies and sub-band states of the titania films. An optimum titania thin film is created at temperatures not higher than 90 °C, regarding sponge-like morphology with pore sizes of 25-30 nm, porosity of up to 71% near the sample surface, and crystallinity of titania in the rutile phase. The low temperature during synthesis is of high importance for photovoltaic applications and renders the resulting titania films interesting for future energy solutions.

Low temperature crystallisation of mesoporous TiO2

“…by the transfer of pre-sintered porous films 21 or the prefabrication of µm-sized mesostructured crystalline building blocks 22 . The use of titanate-based precursors has recently been presented as a viable route to crystalline TiO 2 networks at low temperatures 23 . Other means of crystallisation that are not temperature-induced include the oriented attachment of nanocrystals 24 or solution-based growth of TiO 2 under non-equilibrium conditions with exposed high-energy {001} facets 25,26 .…”

Low‐Temperature Sol‐Gel Synthesis of Nanostructured Polymer/Titania Hybrid Films based on Custom‐Made Poly(3‐Alkoxy Thiophene)

“…The UV/Vis characterization reveals an absorption behavior similar to that of P3HT in the visible region, which is favorable with respect to photoelectronic applications. [34] Atomic Force Microscopy (AFM): The topography of the hybrid films was recorded by AFM (JEOL JSPM 5200) in the tapping mode. The crystallinity was confirmed by GIWAXS measurements which revealed that both the titania and the P3EOT component are crystalline in the hybrid film, promising hole and electron conductivity, respectively.…”

“…[28] Different approaches towards low-temperature synthesis of titania have been described in the literature. [34] Poly(3-alkoxy thiophene) is derived from poly(3-hexyl thiophene) (P3HT)-which is a commonly used polymer for optoelectronical applications [35][36][37] -where the hexyl side chains are substituted by poly(ethylene oxide) side chains (see the Experimental Section for details). Other methods based on titanium tetrachloride lead to nanoparticles in solutions, [31][32][33] but not to nanostructured thin films.…”

Hybrid Photovoltaics – from Fundamentals towards Application

“…Rawolle et al showed that the precursor ethylene glycol modified titanate (EGMT) could be used instead of the frequently applied precursors TTIP. [197] With EGMT the crystal phase of titania was deliberately tunable from anatase to rutile by changes of the pH value. [198] Annealing at 90 °C was sufficient to get mesoporous titania films where well-developed crystallites of rutile phase resided in the pore walls of the network structure.…”