Novel vapor texturing method for EFG silicon solar cell applications

This paper presents an acidic texturing and a novel vapor texturing method for Edge-defined Film-fed Growth (EFG) multi-crystalline silicon (mc-Si) wafers. P-type EFG mc-Si wafers with resistivity 0.5–2 Ω cm and thickness of 300±70 μm were textured with acidic solution using HF:HNO3:CH3COOH. The reflectance decreased as the acid etching proceeded and then saturated when the etching depth reached 10 μm. The isotropic etching of acid texturing resulted in minimum reflectance of 13%. For vapor texturing, the vapor particles were generated by adding silicon to HF:HNO3 acidic solution. Initially silicon was oxidized with HNO3 vapor particles. The nano-pore sized SiF62−SiF62− ion formed over the EFG mc-Si wafer acted as a barrier on the Si surface. The HF vapor particles then dissolved the formed SiO2 effectively by passing through the nano-pores of SiF62−SiF62− ion and etched the EFG mc-Si wafer. The anisotropic etching of vapor textured wafers resulted in an etching depth of about 2.78 μm with reflectance of 5%. The EFG mc-Si solar cell fabricated with acid texturing had VOC of 592 mV, JSC of 27.71 mA/cm2 and efficiency of 12.85% while the cell with novel vapor texturing showed VOC of 597 mV, JSC of 29.61 mA/cm2 and efficiency of 13.54%.

► We carried the novel vapor texturing of EFG mc-Si with HF:HNO3 acid etching solution. ► Vapor texturing of EFG mc-Si wafers gives reduced reflectance than acid textured wafers. ► Acid textured wafers resulted in micrometer level texturing whereas vapor textured wafers resulted in nano-scale texturing. ► Vapor etching mechanism was discussed theoretically and analyzed by their reflectance. ► Solar cell fabricated with vapor textured wafers resulted in best efficiency.