In this study, the three-dimensional (3D) nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by electron tomography. Morphologies suggested by previous experimental evidence were, for the first time, observed directly with a nanometer resolution and studied in detail. After annealing treatment, either at elevated temperature or during slow solvent evaporation, genuine 3D nanoscale networks are formed with high crystalline order and favorable concentration gradients of both P3HT and PCBM through the thickness of the photoactive layer. These favorable morphological changes account for a considerable increase of the power conversion efficiency in corresponding solar cell devices.

To get an efficient organic solar cell, as much light as possible should be absorbed by the photoactive layer; as a consequence, thick layers should be preferable. However, it is often observed that much thinner photoactive layers result in more efficient devices than the corresponding thicker layers absorbing more light. Besides light absorption, other aspects such as efficient exciton dissociation, charge transportation, and charge collection are of crucial importance, and all of them are strongly influenced by the volume morphology of the photoactive layer. In this study of bulk-heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM), we show that the resulting P3HT/ PCBM morphology is strongly determined by the layer thickness because the kinetics of solvent evaporation and crystallization is different in films of different thickness. For the preparation conditions chosen in this study, an optimum morphological organization of the photoactive layer characterized by high crystallinity of P3HT, viz. numerous crystalline P3HT nanowires forming a genuine three-dimensional network, and enrichment of crystalline P3HT closer to the hole collecting electrode can only be achieved for relatively thin (100 nm) P3HT/PCBM layers. Corresponding devices absorb only a limited fraction of all available photons but have the highest efficiency.

We have investigated the morphology of heterostructured GaP-GaAs nanowires grown by metal-organic vapor-phase epitaxy as a function of growth temperature and V/III precursor ratio. The study of heterostructured nanowires with transmission electron microscopy tomography allowed the three-dimensional morphology to be resolved, and discrimination between the effect of axial (core) and radial (shell) growth on the morphology. A temperature- and precursor-dependent structure diagram for the GaP nanowire core morphology and the evolution of the different types of side facets during GaAs and GaP shell growth were constituted.

Conductive multiwall carbon nanotube/polystyrene (MWCNT/PS) composites are prepared based on latex technology. MWCNTs are first dispersed in aqueous solution of sodium dodecyl sulfate (SDS) driven by sonication and then mixed with different amounts of PS latex. From these mixtures MWCNT/PS composites were prepared by freeze-drying and compression molding. The dispersion of MWCNTs in aqueous SDS solution and in the PS matrix is monitored by UV-vis, transmission electron microscopy, electron tomography and scanning electron microscopy. When applying adequate preparation conditions, MWCNTs are well dispersed and homogeneously incorporated in the PS matrix. The percolation threshold for conduction is about 1.5 wt% of MWCNTs in the composites, and a maximum conductivity of about 1 S m À1 can be achieved. The approach presented can be adapted to other MWCNT/polymer latex systems.

Nickel-based metallic foams are commonly used in electrochemical energy storage devices (rechargeable batteries) as both current collectors and active mass support. These materials attract attention as tunable electrode materials because they are available in a range of chemical compositions, pore structures, pore sizes, and densities. This contribution presents structural, chemical, and electrochemical characterization of Ni-based metallic foams. Several materials and surface science techniques (transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), focused ion beam (FIB), and X-ray photoelectron spectroscopy (XPS)) and electrochemical methods (cyclic voltammetry (CV)) are used to examine the micro-, meso-, and nanoscopic structural characteristics, surface morphology, and surface-chemical composition of these materials. XPS combined with Ar-ion etching is employed to analyze the surface and near-surface chemical composition of the foams. The specific and electrochemically active surface areas (As, Aecsa) are determined using CV. Though the foams exhibit structural robustness typical of bulk materials, they have large As, in the range of 200-600 cm(2) g(-1). In addition, they are dual-porosity materials and possess both macro- and mesopores.