title: Hierarchically structured titania films prepared by polymer/colloidal templating.
abstract: Hierarchically structured titania films for application in hybrid solar cells are prepared by combining microsphere templating and sol-gel chemistry with an amphiphilic diblock copolymer as a structure-directing agent. The films have a functional structure on three size scales: (1) on the micrometer scale a holelike structure for reduction of light reflection, (2) on an intermediate scale macropores for surface roughening and improved infiltration of a hole transport material, and (3) on a nanometer scale a mesoporous structure for charge generation. Poly(dimethyl siloxane)-block-methyl methacrylate poly(ethylene oxide) (PDMS-b-MA(PEO)) is used as a structure-directing agent for the preparation of the mesopore structure, and poly(methyl methacrylate) (PMMA) microspheres act as a template for the micrometer-scale structure. The structure on all levels is modified by the method of polymer extraction as well as by the addition of PMMA particles to the sol-gel solution. Calcination results in structures with increased size and a higher degree of order than extraction with acetic acid. With addition of PMMA a microstructure is created and the size of the mesopores is reduced. Already moderate microstructuring results in a strong decrease in film reflectivity; a minimum reflectivity value of less than 0.1 is obtained by acetic acid treatment and subsequent calcination.
authors.affiliation: Physik-Department E13, Technische Universitat Munchen, James-Franck-Strasse 1, 85747 Garching, Germany.
authors.forename: Gunar
authors.initials: G
authors.lastname: Kaune
authors.forename: Mine
authors.initials: M
authors.lastname: Memesa
authors.forename: Robert
authors.initials: R
authors.lastname: Meier
authors.forename: Matthias A
authors.initials: MA
authors.lastname: Ruderer
authors.forename: Alexander
authors.initials: A
authors.lastname: Diethert
authors.forename: Stephan V
authors.initials: SV
authors.lastname: Roth
authors.forename: Maria
authors.initials: M
authors.lastname: D'Acunzi
authors.forename: Jochen S
authors.initials: JS
authors.lastname: Gutmann
authors.forename: Peter
authors.initials: P
authors.lastname: Müller-Buschbaum