A Study Of Acidic Texturization Of Multi-Crystalline Silicon And Surface Modification Of Diamond Wire Sawn Multi-Crystalline Silicon Wafers By Pre-Treatment

Surface chemical etching is widely used in solar cells to reduce light reflection.In the existing texturization technologies for multi-crystalline silicon?mc-Si?solar cells,the conventional HF/HNO₃/H₂O wet acid etching method is the most widely used one because of its advantages of low cost and stable effect.However,it encountered obstacles when it was used in diamond wire sawn?DWS?mc-Si wafers.The light reflectivity of the DWS wafers is high after texturized by this method,and the obvious saw marks generated by the DWS process can be seen clearly.As a new technology for slicing Si wafer,the DWS process has the advantages of high cutting efficiency,low Si loss,energy saving,environmental protection and low processing cost compared with the conventional slurry wire saw?SWS?technology.In order to promote the industrialization of the DWS process,it is necessary to develop a new low-cost texturization technology matching the DWS mc-Si wafers,so as to keep the mc-Si wafers'market advantages of low cost and high efficiency.In this paper,the etching reaction of mc-Si wafers in HF/HNO₃/H₂O acid solution is systematically studied.Based on this,the pretreatment technologies for the DWS mc-Si wafers are developed by physical or mechanical methods to improve its surface state,so as to achieve the reaction conditions of wet acid texturization process and to prepare better texture structure.The main research contents are as follows.1)The etching process of mc-Si wafers was studied.The effects of solution ratio,etching reaction time,mass transfer rate and surface state of silicon wafers on the texture formation in HF/HNO₃/H₂O system were analyzed and discussed.The experimental results show that the controllability of acid etching reaction process and the etching texture are affected by different etching solution ratios.The texture size of silicon wafer surface increases first and then decreases with time during etching reaction process.It is necessary to precisely control the etching reaction time to form suitable pits in depth.The solution viscosity factors will also affect the reaction speed.The mass transfer process of reactant and products will affect the corrosion rate of silicon and etch pit morphology.The surface area with more surface damage defect structure of silicon wafers have higher reactivity and are more prone to etching reactions to form pit structures.2)The surface of DWS mc-Si wafer is densely scratched and unevenly damaged.Its smooth area is densely amorphous silicon structure with acid corrosion resistance.These surface characteristics of DWS mc-Si wafer make it difficult to etch the ideal texture in HF/HNO₃/H₂O wet acid etching system.3)The pretreatment by ultrasonic vibration method can produce damage structure distribution on the surface of DWS mc-Si wafers similar to that of SWS mc-Si wafers.The pre-treated DWS mc-Si wafers were etched in conventional acid etching solution,and their textures are similar to that of SWS mc-Si wafers.The light reflectivity?600nm?of pre-treated silicon wafers is about 3%lower than that of untreated silicon wafers.4)The pretreatment by high temperature phase transformation method can completely transform the amorphous phase in the smooth surface of DWS mc-Si wafers into crystalline phase.After phase transformation,it is easier to react with HF/HNO₃/H₂O etching solution,and there are significant differences in etching depth,texture morphology and light reflectivity between the pre-treated DWS mc-Si wafers and the untreated ones.The average efficiency of the solar cell based on the pre-treated DWS mc-Si wafers can reach 18.62%,which is close to 18.70%of the SWS mc-Si wafers,and it is about 0.15%higher than the 18.47%of the untreated DWS mc-Si wafers.This method is expected to provide a possible technical path for acid etching of DWS mc-Si wafers.