Hierarchical rutile TiO2 aggregates: A high photonic strength material for optical and optoelectronic devices

Hierarchical monodisperse and poly-disperse rutile TiO2 aggregates featuring excellent light scattering properties were synthesized by a simple hydrolysis route at low temperature using sucrose as the structure directing agent. Various characterization techniques revealed that sucrose played a key role in controlling the shape and size distribution of hierarchical aggregates. The aggregates are formed by nano-sized crystallites and, therefore, are able to offer both a large specific surface area and strong light scattering behaviour. Films composed of monodisperse 465 nm rutile spheres coupled to a layer of commercial P25 anatase nanoparticles manifested a large photonic strength through the combination of a high haze ratio and a large back scattering-to-forward scattering ratio. The hierarchical rutile TiO2 aggregates when employed as the sole working electrode in DSSCs, achieved a 5.16% power conversion efficiency which is higher than that of commercial P25 (5.04%) with same thickness. In addition, the overall conversion efficiency of 7.26% was achieved when hierarchical aggregates were used as the light scattering overlayer of photoanode. The significant enhancement in overall conversion efficiency was attributed to the large photon absorption by increasing path length of photons due to the multiple scattering by hierarchical aggregates. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.