Preparation method of back membrane capable of improving conversion efficiency of single-faced PERC cell

The invention relates to a preparation method of a back membrane capable of improving conversion efficiency of a single-faced PERC cell. The method includes the steps of preparing an aluminum oxide membrane, preparing a silicon oxide membrane on the back face, preparing a silicon oxynitride membrane on the back face and preparing a double-layer silicon nitride membrane on the back face. A siliconwafer back membrane structure obtained by an existing production process generally is only provided with an aluminum oxide layer and a silicon nitride layer, while the method provided by the inventionadds the high-density silicon oxynitride membrane and silicon oxide membrane on the back membrane. The silicon oxynitride membrane with the high refraction index can well increase reflection of long-waveband sunlight by the back face of the cell, so long wave light enters a silicon wafer body again, absorption of the long wave light is increased, and therefore open-circuit voltage and current ofthe cell are increased so a