ZnO sphere made of aggregated nanoparticles with a mean diameter of 19 nm have been prepared by the forced thermohydrolysis in polyol medium technique which is a versatile synthesis method for the preparation of metal oxide particles with controlled properties. The sphere were polydisperse and sub-micrometric in size. Porous layers have been prepared using these building blocks. They showed a large specific surface area and were highly light scattering in the visible wavelength region. We have investigated the performances of D149-dyesensitized solar cells (DSSCs) based on these layers. The annealing temperature as well as the layer thickness has been optimized. Finally the best cells reached an overall conversion efficiency of about 4.7% for layers with a thickness ranging between 27 and 35 μm and annealed at 400°C.
Core-shell ZnO/γ-Fe2O3 nanoparticles were prepared via a simple method using forced hydrolysis of acetate metallic salts in a polyol medium. Two types of morphologies can be easily obtained: (i) quasi-spherical ZnO core 20 nm in diameter coated with a continuous shell with 3 nm in length, (ii) rod-like ZnO decorated with γ-Fe2O3 nanoparticles. The ZnO nanorods are 80 nm in diameter and 400 nm in length. The maghemite (γ-Fe2O3) nanoparticles with 5 nm in diameter are strongly bonded to ZnO, well separated from each other and form a monolayer on the surface of ZnO nanorods. In both systems, coating ZnO by γ-Fe2O3 inhibits the surface defects and thus enhances the UV luminescence. The two systems present a superparamagnetic behavior with blocking temperature depending on the morphology: the decorated ZnO nanorods present a blocking temperature around 6 K whereas this temperature is significantly higher (300 K) for spherical core-shell nanoparticles.