多晶硅中的氧碳行为及其对太阳电池转换效率的影响

认识及控制多晶硅中杂质行为对于实现低成本、高效率多晶硅太阳电池有着重要的意义.利用红外光谱技术研究了定向凝固多晶硅锭中不同部位材料热处理前后的氧浓度、碳浓度变化,结合少子寿命、光电转换效率、内量子效率等电池性能,探索不同含量的氧、碳杂质对电池性能影响的物理机制.提出一种考虑碳影响的氧沉淀生长模型,并模拟了热处理后氧沉淀的尺寸分布和数量.研究发现,碳除了使利用硅锭顶部材料制备得到的电池转换效率降低外,还是决定氧沉淀作用的重要因素.由于碳含量多造成中部材料氧沉淀的尺寸大、数量多,引起缺陷,增加复合,而碳在底部 关键词： 氧 碳 太阳电池 转换效率

Oxygen and carbon behaviors in multi-crystalline silicon and their effect on solar cell conversion efficiency

Understanding and controlling the impurity behavior are important for low-cost and high-efficiency of multi-crystalline silicon solar cells. We employ the infrared spectroscopy to study the change of oxygen and carbon concentrations after thermal treatment in different parts of multi-crystalline silicon ingots grown by directional solidification technology. In correlation with the solar cell performances such as the minority carrier lifetime, photoelectric conversion efficiency and internal quantum efficiency, we investigate the physical mechanism of the effects of various concentrations of oxygen and carbon on cell performance. We propose an oxygen precipitation growth model considering the influence of carbon to simulate the size distribution and concentration of oxygen precipitation after the thermal treatment. It is found that carbon not only deteriorates the efficiency of the cells made from the silicon from the top part of the ingot, but also plays an important role in the effect of oxygen precipitation: enhancing the size and the quantity of oxygen precipitation in the silicon from the middle part of the ingot, which induces the defect and increases the recombination; while resulting in the small size and low quantity of oxygen precipitation in the silicon from the bottom part due to the low carbon content, thereby improving the cell efficiency through gettering impurities. We further demonstrate the complex behaviors of oxygen and carbon by a two-step thermal treatment technique, from which we point out that the two-step thermal treatment is applicable only to the improvement of the efficiency of solar cells from the bottom part of multi-crystalline silicon ingots.