影响多晶硅太阳电池转换效率的关键原因研究

The thermal field of the multicrystalline silicon ingot furnace and the growth process are both simulated to further investigate the relation the crystal growth velocity,solid-liquid interface shape with the conversion efficiency of the multicrystalline silicon solar cell. The crystal growth CGSim simulation software is used to simulate the forefront evolution process of silicon crystallization and the melt flow characteristics, to analyze the dislocation density,impurities distribution. The high quality of silicon ingot can be got by adjust the heating zone, while avoiding the possibility of overheating or excessive temperature region, so that the multicrystalline silicon can grow along the isothermal convex solidification line, and the minority carrier lifetime of silicon wafer will be improved, the dislocation density of the edge of silicon ingots reduce. The conversion efficiency of the multicrystalline silicon solar cell combining with the technology of light-doping forming shallow P-N junction will reach to 18.0%-18.4%.

本项目将多晶硅铸锭炉热场模拟与晶体生长模拟进行有机结合，围绕长晶过程中长晶速度、固-液界面形状重要参数，仿真多晶硅结晶前沿演变过程，评估多晶硅中柱状晶所占比例、晶粒大小及分布均匀性对多晶硅太阳电池光电转换效率的影响，找到少子寿命、晶粒尺寸大小及位错密度等与电池效率之间对应关系，并以之来确定晶锭质量的方法。注重热场设计、晶体生长和杂质输运之间相互关系，保证多晶硅在微凸凝固等温线上定向生长，通过不断改进长晶和退火温度梯度变化，优化高效多晶硅长晶和退火工艺，减少长晶过程中位错繁殖速度及边缘锭和四角锭中斜角晶、枝蔓晶比例，提高硅锭及硅片少子寿命和分布的均匀性，结合轻掺杂浅结高效光伏电池工艺，使高效多晶硅太阳电池光电转换效率达到18.0%-18.4%水平。

从整个生产环节开始，研究并改造多晶硅铸锭炉热场，研究晶体定向生长规律，通过引入同质和异质籽晶进行引导定向生长和采集晶体生长速度，控制晶体生长速度；围绕多晶硅结晶前沿演变以及熔体流动特性，创造性研究出复熔技术，有效地控制结晶前沿晶体生长多样性，减少枝蔓晶和斜角晶，生产出较高质量的多晶硅硅片。采用分析硅片的晶粒尺寸大小和晶粒数，在评估晶体的晶粒分布均匀性及方面编写了基于VC++和matlab图像分析软件，有利于生产高效率硅片，经过各大电池厂家试用，获得较好的反馈。