232
O. Yasko et al.
the cost of solar cells. Unfortunately, most of these substrates are characterized by
silicide formation at 1023 K. Therefore, graphite is more promising material because
of its lower reactivity.
The further development of methods for silicon electrodeposition onto different
materials was made in fluoride [1, 3] and chloride–fluoride [4, 6] melts.
The purpose of the present study is the electrodeposition of high-purity silicon
onto graphite substrate as adherent coating and the investigation of the deposits
morphology dependence on the conditions of electrodeposition.
2 Materials and Methods
Instruments, chemicals, and main experimental conditions used during this work
were similar to those used [5]. Rod cathode was made of PGM-7 graphite. Previous
studies have shown that the optimal concentration of K2SiF6 is 8–14 mol% in binary
eutectic KF-LiF mixture (765 K). Electrodeposition was carried out at 1023 K in a
graphite crucible, which was also used as the anode.
Morphology of deposits was studied by methods of optical and scanning electron microscopy. Analysis of impurities was made using electron microprobes and
emission spectroscopy methods.
List of abbreviations
CNRS the National Center for Scientific Research of the French Ministry of
Education and Research
3 Results and Discussion
Electrodeposition
For dense silicon coating deposition, concentration of K 2 SiF 6 was maintained within
limits of 8–14 mol% at a constant potential. Electrodeposition was carried out at
potential −0.75 ± 0.05 V versus Pt or Ag reference electrode. Current strength
was varied within limits of 10–100 mA/cm
2 . During the deposition, uniform dense
deposits of silicon were obtained.
Morphology
Silicon coating with grains of wedge shape up to 1 mm thick was obtained by
electrolysis during 5–6 h. Electrodeposited silicon was easily separable from the
graphite substrate. The cross section of deposits (Fig. 1) indicates 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 (Fig. 2). Larger grains (up to 750 nm) were formed
by the electrolysis for more than 5–6 h.
O. Yasko et al.
the cost of solar cells. Unfortunately, most of these substrates are characterized by
silicide formation at 1023 K. Therefore, graphite is more promising material because
of its lower reactivity.
The further development of methods for silicon electrodeposition onto different
materials was made in fluoride [1, 3] and chloride–fluoride [4, 6] melts.
The purpose of the present study is the electrodeposition of high-purity silicon
onto graphite substrate as adherent coating and the investigation of the deposits
morphology dependence on the conditions of electrodeposition.
2 Materials and Methods
Instruments, chemicals, and main experimental conditions used during this work
were similar to those used [5]. Rod cathode was made of PGM-7 graphite. Previous
studies have shown that the optimal concentration of K2SiF6 is 8–14 mol% in binary
eutectic KF-LiF mixture (765 K). Electrodeposition was carried out at 1023 K in a
graphite crucible, which was also used as the anode.
Morphology of deposits was studied by methods of optical and scanning electron microscopy. Analysis of impurities was made using electron microprobes and
emission spectroscopy methods.
List of abbreviations
CNRS the National Center for Scientific Research of the French Ministry of
Education and Research
3 Results and Discussion
Electrodeposition
For dense silicon coating deposition, concentration of K 2 SiF 6 was maintained within
limits of 8–14 mol% at a constant potential. Electrodeposition was carried out at
potential −0.75 ± 0.05 V versus Pt or Ag reference electrode. Current strength
was varied within limits of 10–100 mA/cm
2 . During the deposition, uniform dense
deposits of silicon were obtained.
Morphology
Silicon coating with grains of wedge shape up to 1 mm thick was obtained by
electrolysis during 5–6 h. Electrodeposited silicon was easily separable from the
graphite substrate. The cross section of deposits (Fig. 1) indicates 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 (Fig. 2). Larger grains (up to 750 nm) were formed
by the electrolysis for more than 5–6 h.