International audienceWe summarize our research studies on the synthesis of silicon and germanium nanocrystals and their application to the growth of a variety of thin films, spanning the range from fully disordered amorphous up to fully ordered crystalline. All these films are deposited in a standard radio-frequency glow discharge system at low temperature (~200 °C). We show how the plasma synthesis of silicon nanocrystals, initially a side effect of powder formation, has become over the years an exciting field of research which has opened the way to new opportunities in the field of materials deposition and their application to optoelectronic devices. Our results suggest that epitaxy requires the melting/amorphization of the nanocrystals upon impact on the substrate, the subsequent epitaxial growth being favored on (100) c-Si substrates. As a consequence, the control of the impact energy is a critical aspect of the growth which will require new strategies such as the use of tailored voltage waveforms

We report on light-induced electrical and macroscopic changes in hydrogenated polymorphous silicon (pm-Si:H) PIN solar cells. To explain the particular light-soaking behavior of such cells -namely an increase of the open circuit voltage (Voc) and a rapid drop of the short circuit current density (Jsc) -we correlate these effects to changes in hydrogen incorporation and structural properties in the layers of the cells. Numerous techniques such as current-voltage characteristics, infrared spectroscopy, hydrogen exodiffusion, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry are used to study the light-induced changes from microscopic to macroscopic scales (up to tens of microns). Such comprehensive use of complementary techniques lead us to suggest that light-soaking produces the diffusion of molecular hydrogen, hydrogen accumulation at p-layer/substrate interface and localized delamination of the interface. Based on these results we propose that light-induced degradation of PIN solar cells has to be addressed from not only as a material issue, but also a device point of view. In particular we bring experimental evidence that localized delamination at the interface between the p-layer and SnO2 substrate by light-induced hydrogen motion causes the rapid drop of Jsc.