Improvement of thin film polycrystalline silicon solar cells is in the center of interest both at the Department of Silicon Photovoltaics of the Helmholtz-Zentrum Berlin (HZB), see http://www.helmholtz-berlin.de/forschung/enma/si-pv/. HZB uses a traditional method of hydrogen plasma. Water vapour is tested at the Institute of Physics as a cheaper alternative. During the cooperation, Peter Pikna from FZU has revealed unexpected positive effect of hydrogen pressure on solid-phase crystallized thin film of polycrystalline silicon solar cells. The figure illustrates variations of plasma distribution during the hydrogenation, which are related to the passivation effect. Microscopic measurements of the samples are being done at FZÚ.