Novel low cost chemical texturing for very large area industrial multi-crystalline silicon solar cells

Multi-crystalline silicon surface etching without grain-boundary delineation is a challenging task for the fabrication of high efficiency solar cells. The use of sodium hydroxide-sodium hypochlorite (NaOH-NaOCl) solution for texturing a multi-crystalline silicon wafer surface in a solar cell fabrication line is reported in this paper. The optimized etching solution of NaOH-NaOCl does not have any effect on multi-crystalline silicon grain boundaries and it also has excellent isotropic etch characteristics, which ultimately helps to achieve higher values of performance parameters, especially the open circuit voltage (V-oc) and fill factor (FF), than those in the case of conventional silicon texturing. Easy control over the reaction of the NaOH-NaOCl solution is also one of the major advantages due to which sophistication in controlling the temperature of the etching bath is not required for the industrial batch process. The FTIR analysis of the silicon surface after etching with the current approach shows the formation of Si-Cl bonds, which improves the quality of the diffused junction due to chlorine gettering during diffusion. We are the first to report 14-14.5% efficiency of very large area (150 mm x 150 mm) multi-crystalline silicon solar cells using a NaOH-NaOCl texturing approach in an industrial production line with a yield greater than 95%.