Numerical Simulation Of Crystal Growth Of Multi-crystalline Silicon Based On CA-LBM Coupling Method

The ingot multi-crystalline silicon has been widely used in the manufacture of solar cells with the advantages of high photoelectric conversion rate and relatively low production cost.The numerical simulation technique can simulate the crystal growth process and guide the process experiment.In this paper,the cellular automata and lattice Bolzmann method(CA-LBM)coupling model was established,and the crystal growth process of ingot multi-crystalline silicon,temperature field as well as flow field during the growth of crystal were simulated.The effects of different nucleation methods,capture modes and initial solution temperature on the crystal were analyzed.In the CA-LBM coupling model,the CA calculates the nucleation,growth,capture and transformation of the crystal,and the LBM calculates the temperature field required for growth as well as the flow field in the solution.They share a set of grids and are coupled to each other by the action of the temperature field.The temperature field and the flow field are coupled with each other by discrete velocity and external force source.The model is compiled into a C ++ program to simulate the calculation and the results are verified with the literature,which proves the feasibility and correctness of the model.In the ingot multi-crystalline silicon directional solidification process,the heat spread from top to bottom,it is not balanced so that the density of the solution is not balanced,resulting in the natural convection generated in the solution.The crystals are nucleated at the bottom and gradually grow up with the competitive phenomenon,and the eight-neighbor capture model is more representative of the competition phenomenon in the crystal growth process than the four-neighbor capture model.Compared with the random nucleation model,the crystal is more uniform with the bottom of the induced nucleation model.Under the forced convection condition,four flow vortices appear in the solution.The initial solution temperature has a great influence on the crystal growth.When the initial temperature is low,the latent heat of crystallization released by crystal growth will diffuse in both directions of crystal and solution,and the crystal growth rate is large,the crystal competition is intense.There is a zigzag facet at the solid-liquid interface,and the lower the temperature the greater the height of the sawtooth.When the initial melt temperature is high,the crystallization latent heat only diffuses into the crystal,and the main phenomena include small crystal growth rate,weak competition growth,flat solid-liquid interface during directional solidification of silicon.