A Study Of High Performance Multi-crystalline Silicon Cast Made By Nucleation From Silicon Powders

Multicrystalline silicon wafers are mainly grown by directional solidification,which is one of the most important substrates for solar cell materials because of its low cost and high yield.The traditional multicrystalline silicon ingot is nucleated on the silicon nitride coating on the bottom of the quartz crucible,with large grains and high dislocation density.The use of polysilicon as a seed-inducing polysilicon ingot growth since 2011 has also been referred to as high-performance multicrystalline silicon,which is a significant advance in the photovoltaic industry.Different from the traditional growth method of large-grained polycrystalline silicon ingots,the seed crystal-induced multicrystalline silicon ingots have fine and uniform grain size,more uniform grain orientation distribution,a high proportion of random grain boundaries and lower dislocation density,and the cell conversion efficiency have a Significantly increase and narrower distribution.At present,the main manufacturers of multcrystalline isilicon wafers have turned to the use of seed crystals to assist in the growth of polycrystalline silicon ingots.Fluidized bed granular silicon or Siemens polycrystalline silicon are the most commonly used seed crystals for seed crystal selection.The seed crystals located at the bottom of the crucible provide many Epitaxially grown nucleation sites,the silicon melt is easily seeded from the seed crystal at a certain degree of undercooling.However,the polysilicon seeding induction technology also has the disadvantages that cannot be ignored.First,it needs precise thermal field control at the bottom of the crucible to retain part of the seed crystals.Therefore,the melting time of this method is longer than the traditional one,resulting in a decrease in productivity.Second,the flow The large specific surface area of the Fluidized bed granular silicon or Siemens polysilicon seed crystal easily causes impurity contamination.Therefore,polycrystalline silicon seeded polycrystalline silicon ingots exhibit more low minority carrier lifetime regions at the bottom.In this study,different silicon powder nucleating agents were prepared for the growth of High-performance multicrystalline silicon ingots.It was found that the use of 5-30 μm silicon powder nucleating agents facilitates the formation of small grain nucleuses,and the minority ingot lifetime of silicon ingots is better.The low lifetime length at the bottom of the ingot is significantly shorter than that of the seed-assisted High-performance multicrystalline silicon ingot,which increases the output rate of the silicon ingot by more than 3%,and reduces the ingot time and the energy consumption of the ingot to a certain extent,thereby reducing the cost of the ingot.At the same time,the efficiency of the solar cells prepared by the High-performance multicrystalline silicon wafers grown by this method is equivalent to that of seed-assisted High-performance multicrystalline silicon wafers.In addition to the nucleation at the bottom of the crucible,this topic also studied the use of silicon powder to prepare a functional coating on the crucible sidewall.The coating can be nucleated into small grains on the side wall of the silicon ingot to significantly reduce the silicon brick in the edge region of the silicon ingot.The width of the red edge decreased from 36 mm to 9 mm.The width of the black edge of the PL test on the silicon wafer was significantly reduced,and the crystal defects were also reduced to a certain extent.The carbon and oxygen content was less different from that of the seed-assisted silicon ingot and the prepared solar cell efficiency increased by 0.05%.