Wettability and infiltration of molten Si on SiO2 substrate containing porous Si3N4 coating: Influence of α-Si3N4 coating and β-Si3N4 coating

Photovoltaic (PV) multicrystalline silicon (Si) is currently grown in SiO2 crucible with porous alpha-Si3N4 coating, which serves as interfacial releasing agent to avoid sticking. Compared with alpha-Si3N4, beta-Si3N4 should be another potential coating material, due to the same chemical composition and better structural stability. To verify this conception, it's of great importance to ascertain the wetting behavior and infiltration of Si/beta-Si3N4/SiO2 ternary system. In this study, the sessile drop technology and micro-structural analysis method were used to investigate interfacial wetting behavior and infiltration of Si drop on different coatings, which are alpha-Si3N4 coating, beta-Si3N4 coating and silica modified beta-Si3N4 (beta-Si3N4@SiO2) coating. The results show that wettability transformation (from non-wetting to wetting) commonly occurs for all coatings, as well as infiltration. The beta-Si3N4 coating displays much shorter non-wetting duration and severer infiltration than alpha-Si3N4 coating. Compared with beta-Si3N4 coating, the beta-Si3N4@SiO2 coating exhibits significantly extended non-wetting duration and considerably delayed infiltration. These differences about wettability and infiltration are strongly associated with O content in all coatings and de-oxidation. This work clarify the wettability/infiltration differences between alpha-Si3N4 coating and beta-Si3N4 coating in Si/Si3N4/SiO2 ternary system, and could be used to develop novel beta-Si3N4 coating with low cost for PV multicrystalline Si manufacture.