【作者】 张伟娜；

【导师】 谭毅；

【作者基本信息】 大连理工大学 ， 材料学， 2008， 硕士

【摘要】 太阳能电池中使用的硅材料，不论其在工作时处于何种晶体类型，其原材料都是高纯多晶硅，纯度在6N(99.9999％)以上。目前普遍认为采用冶金法，使用廉价的工业硅制备太阳能级多晶硅是大幅度降低太阳能电池成本的途径之一。本文中的冶金多晶硅即由冶金法制备的多晶硅材料。太阳能电池中使用的多晶硅除了对纯度有一定要求之外，电阻率的高低也是最重要的性能参数之～，一般情况下，其数值应在0.5-6Ω·cm之间，而且对于其均匀程度也有要求。由于杂质分布不匀，电阻率也不均匀。电阻率均匀性包括纵向电阻率均匀度、断面电阻率均匀度和微区电阻率均匀度，它直接影响器件参数的一致性和成品率。电阻率是多晶硅材料最重要的参数之一，本文利用四探针电阻率测试仪、金相显微镜、扫描电镜(SEM)、电感耦合等离子发射光谱仪(ICP)、能谱分析(EDS)、X射线衍射仪(XRD)等设备，从密度、晶粒尺寸、组织形态、化学成分、高温扩散金属杂质(铁、钴、镍、铜、锰、铝、锌)到多晶硅晶内及晶界析出物等方面对冶金法制备的多晶硅的电学性能进行了研究。研究结果表明：(1)不同熔炼方式导致多晶硅的密度不同，高密度的多晶硅材料禁带较窄，故电阻率较小。(2)3-4N纯度的多晶硅的电阻率对于不同的组织状态十分敏感，电阻率随晶粒度增加而减小，且沿柱状晶方向电阻率较大；2N和6N多晶硅电阻率对于组织状态并不是十分敏感。(3)金属杂质按照对多晶硅电阻率的影响可分为三类：一类以铁、钴、镍为代表，此类杂质含量超过固溶度以后形成析出相，在多晶硅高温快速冷却至室温时在表面析出，并吸附其他金属杂质在表面一起析出，杂质析出后对电阻率的影响较小；一类以铜和锰为代表，此类杂质在多晶硅中多以沉淀相存在，即使高温快速冷却也不易在多晶硅表面析出，而是留在晶体内部，对电阻率的影响较大；第三类是以铝和锌为代表，此类杂质不会形成沉淀物新相，对电阻率的影响非常复杂。更多还原

【Abstract】 Solar energy is one of the earth’s most abundant renewable resources.The demand for silicon solar cells has recently increased significantly. While the production capacity of silicon solar modules, cells and wafers has been expanded to meet this demand, that of solar silicon feedstock has not grown at the same pace. Solar energy will shortly be in great demand since it is inexhaustible and cleaner than any conventional energy resources. Using relatively inexpensive metallurgical grade silicon (MG-Si) as a starting material for making solar grade silicon (SoG-Si) is believed to be one of the ways to make solar cells less expensive. Impurities in MG-Si will shorten the lifetime of excited carriers in silicon solar cell and disturb electric generation. Hence, the removal of impurities from silicon is a significant issue in silicon solar cell fabrication. Also, the electrical resistivity is one of the most important parameters for multicrystalline silicon. Using the four point resistivity test system, metallographic microscope, scanning electron microscope (SEM), inductively-coupled plasma spectrometer (ICP), energy spectrum analysis (EDS), X-Ray diffraction instrument (XRD) etc., study the influence of density, organization and impurity for the electrical properties of the multicrystalline silicon, this prepared using the metallurgic method are studied. To discuss the pertinency of the impurity elimination process, evaluation of electrical properties of multicrystalline metallurgy silicon with different components such as the magnitude and uniformity of resistivity has been performed.In this paper, some aspect such as the density, grain size, microstructure, chemical constitution, precipitation in the grain boundary etc. are described. It has been found that the electrical resistivity is in direct ratio to the density. And the electrical resistivity is in direct ratio to the grain size when the microstructure is an equi-axis crystal. When it is a columnar crystal, the electrical resistivity that is parallel to the columnar crystal is higher than the electrical resistivity that is vertical to the crystal. In the low-purity multicrystalline silicon, the metal impurity takes the formation of segregation in the grain boundary, the phase of metal silicides, making the electrical resistivity of the multicrystalline silicon lower. But the resistivity of multicrystalline silicon whose purity grade is under 2N or hyper 6N is not variant with different tectologies. There are three kinds of metal impurities in multicrystalline metallurgic silicon. One of them comes into being silisides and then separate out as precipitated phase, such as Fe、Co and Ni. One of them also comes into being silicides, but will not separate out of silicon, such as Cu and Mn. And the influence of the indwelling silicides to the resistivity is larger. The third impurity can’t come into being silicides, such as Al. And the influence of the third impurity to resistivity of multicrystalline silicon is very complex.更多还原