Electronic properties of adjoined TiO2 nanocrystals

The discussion of particle attachment effects is indispensable for deeper insights into electronic conduction across grain boundaries and thus essential to photovoltaics. We investigated the condensation of isolated TiO$_{2}$-nanocrystals [1] induced via the application of a simple hydration-dehydration cycle. The resulting particle network shows a mesoporous structure as well as significant changes in the optical absorption properties as investigated by UV-diffuse reflectance spectroscopy. In addition, polarizable conduction band electrons are only observed in the network which consists of adjoined TiO$_{2}$-nanocrystals [2]. Since photo-assisted tunneling between localized states in the oxide particle network represents an important conduction mechanism in dye-sensitised solar cells, UV induced charge separation processes were studied on nanocrystal aggregates using EPR and IR spectroscopy. Corresponding results will be discussed in the light of associated structural data. [1] Berger et al. Chem. Phys. Chem. 2005 6 2104-2112 [2] Elser et al. J. Phys. Chem. B 2006, 110, 7605