Nanocrystalline and ordered mesoporous Titania thin films on Indium tin oxide glass

IANINA L. VIOLI; M. DOLORES PÉREZ; M. CECILIA FUERTES; GALO J. A. A. SOLER-ILLIA

University of California, Santa Barbara

Workshop; Workshop on Emerging Materials for Thin Film Solar Cells; 2011

International Center of Material Research

Mesoporous Titania Thin Films (MTTF) with crystalline framework, high surface area and tunable pore size have received significant attention due to the many relevant applications such as photocatalysis, energy storage and conversion, electrochromism and sensors. In particular, MTTF applied to photovoltaic systems are envisioned as a great promise for the development of next generation, highly efficient, low-cost solar cells. The development of highly crystalline titania that presents controlled and accessible porosity is highly desirable for solar applications. Crystallization into the anatase phase is important to ensure high electron transport and low charge trap concentration. Also, an elevated porosity of the titania network results in enhanced interfacial area that is highly relevant for bulk heterojunction solar cells. Such properties of the titania films are highly dependent on several parameters like post-synthesis thermal treatments and the nature of the substrate. In particular, the development of these nanocrystalline ordered MTTF onto a transparent conducting electrode like ITO is an important subject of study. In this work, ordered MTTF were prepared by sol-gel method onto ITO, and the effect of thermal treatment on the crystallinity of the oxide was studied. Treatment at 550ºC yielded high crystalline walls (analyzed by Grazing Incidence X-Ray diffraction) with significant pore accessibility of the mesoporous structure (studied by Environmental Ellipsometric Porosimetry). Additionally, the effect of inserting a dense (non-porous) thin titania layer at the MTTF-ITO interface was studied. Crystallization of the top mesoporous layer appears not to be affected by thermal treatments on the underlying dense layer; however, the accessible pore volume results to be increased in the 550ºC-treated mesoporous layer by the presence of the dense titania. This porous anatase film with enhanced pore accessibility results in a composite material that represents the first step towards the development of all solid-state hybrid solar cells.