Silicon electrodeposition in molten fluorides

Silicon nucleation process was investigated in molten NaF–KF (40–60 mol%) on silver electrodes in the 820–950 °C temperature range in order to optimize silicon coating operating conditions. Chronoamperometric measurements evidenced that silicon electrodeposition process involved an instantaneous nucleation with diffusion-controlled nuclei growth whatever temperature and Si(IV) ions concentration in the mixture. The overpotential and temperature influence on nucleation sites number was also studied.Silicon deposits were obtained using the same temperature range as nucleation study, for different current densities on substrates: Ni, Ag, Cgraphite and Cvitreous. A sensitive influence of the cathodic substrate on the deposit adherence and roughness was observed and discussed.

► Silicon nucleation study in fluoride salts concludes to an instantaneous nucleation controlled by the Si(IV) ions diffusion.
► Nucleation sites number is favoured by both temperature and over voltage increase.
► Silicon electrodeposition on graphite carbon leads to a dense and well adherent deposit, with a purity higher than 99.9%.