Physico-Chemical nanomaterials science

Electrodeposition of Nanostructured Silicon Coatings onto Different Materials from Halide and Halide-Oxide Melts
Yasko O.M.1, Shakhnin D.B.1, Kublanovsky V.S.2, Malyshev V.V.1,2
1 University “Ukraine”. 23 Lvivska St., Kyiv-03115, Ukraine. 
E-mail: o.yasko@meta.ua
2 Vernadsky Institute of General and Inorganic Chemistry of the NAS of Ukraine. 32/34 Palladina Ave., Kyiv-03142, Ukraine.

The aim of the present study is adherent nanostructured silicon coatings electrodeposition onto different materials and investigation of their morphology depending on the electrodeposition conditions.
For dense silicon coating deposition, K2SiF6 concentration in molten electrolyte was maintained within 8-14 mol. % range. Electrodeposition was carried out at a constant potential -0.75±0.05 V vs. Pt or Ag reference electrode. Current density was varied within 10-100 mA/cm2 range. Under these conditions, uniform dense silicon deposits were obtained.
Morphology of deposits was studied by methods of optical and scanning electron microscopy. Silicon coating with wedge-shaped grains up to 1 mm thick was obtained by electrolysis during 5-6 h. Electrodeposited silicon was easily separable from the graphite substrate. The deposit cross-section shows nodular or dendritic growth up to a few millimeters at the surface of main adherent layer of silicon coating. The grain size was about 250 nm. Larger grains (up to 750 nm) were formed by the electrolysis during more than 5-6 h.
Analysis of impurities was made using electron microprobes and emission spectroscopy method. X-ray phase analysis showed the presence of only polycrystalline silicon in the deposit. In addition, electronic microprobe studies and X-rays scattering energy analysis revealed no impurities. However, levels of Li, Cr, Ni, Fe, Cu, Ag, Mn, Pb, Al impurities up to 0.02% were detected by emission spectroscopy method. The most common impurities are Cu, Fe, Ni and Ag, but the overall level of their concentrations would not impact significantly on the performance of solar cells. Deposits purity level was generally over 99.99%.
Results of measurements by four-probe method showed disagreement of specific resistivity values at different places of electrodeposited silicon. At room temperature, measured resistance of silicon electrodeposited from this system was always greater than 1 Ohm·cm.