Physical and Optical Properties of Microscale Meshes of Ti3O5 Nano- and Microfibers Prepared via Annealing of C-Doped TiO2 Thin Films Aiming at Solar Cell and Photocatalysis Applications

Abstract

Dye-sensitized nanocrystalline solar cells (DSSC) or photoeletrochemical solar cells were firstly described by Gratzel and O’Reagan in the early 1990s (Sauvage et. al., 2010) and they have reached the global photovoltaic market since 2007. Later on, the investments in nanotechnology enabled the rapid development of DSSC cells with nanostructured thin films. According to a review performed by Hong Lin et. al. (Lin et. al., 2009) the numbers of papers focusing on the development of the DSSC cells increased in last decade, being mainly originated in countries such as Japan, China, South Korea, Swiss and USA, where there is an enlarged integration of nanotechnology, electrochemical and polymers research and finantial supported projects like National Photovoltaic Program by Department of Energy (DOE) and NEDO’s New Sunshine from USA and Japan, respectively. Some research groups of the institutions (Kim et. Al., 2010),which have recently obtained efficiencies around 10%, are EPFL (11.2% in 2005) and AIST (10% in 2006). They have used the N719 colorant in devices with area 0.16cm2 and 0.25cm2. On the other hand, Sharp, Tokyo University and Sumitomo Osaka Cell have used the black dye colorant in devices with areas of approximately 0.22cm2, providing the efficiencies of about 11.1%, 10.2% and 10% in the years 2006, 2006 and 2007, respectively. In 2006, Tokyo University has also reached the efficiency of 10.5% in devices with 0.25cm2 area, but using -diketonide colorant. Initially, the DSSC (Sauvage et. al., 2010) were based on a nanocrystalline semiconductor (pristine titanium dioxide) coated with a monolayer of charge-transfer dye, with a broad absorption band (generally, polypyridyl complexes of ruthenium and osmium), to sensitize the film. The principle of operation of these devices can be divided into: a) the photo-current generation that occurs when the incident photons absorbs in the dye, generates electronhole pairs and injects electrons into the conduction band of the semiconductor (Ru2+ -> Ru3+ + e-), and b) the carrier transport that occurs because of the migration of these electrons through the nanostructured semiconductor to the anode (Kim et. al., 2010). Thus, since this device requires an electrode with a conduction band with a lower level than the dye one, the