【作者】 刘艳娇；

【导师】 谭毅；

【作者基本信息】 大连理工大学 ， 材料学， 2010， 硕士

【摘要】 太阳电池用晶体硅除了对纯度的要求之外,电学性能也十分重要。杂质和缺陷在晶体硅中会影响其电学性能的稳定性和器件参数的一致性。单晶硅没有晶界的影响,电性能相对稳定,转换效率普遍比多晶硅高,但高成本又制约其应用。多晶硅虽然成本较低,但材料中的各种缺陷,如晶界、位错、微缺陷,以及高浓度的杂质,是影响其电池转换效率的重要因素。到目前为止,电子级晶体硅材料中杂质和缺陷的研究比较深入,但4N-6N的硅材料中杂质和缺陷对电学性能的影响尚不明确。因此,研究此纯度范围单晶硅和多晶硅中缺陷、杂质的分布规律以及其对电性能的影响具有重大意义。本文利用四探针电阻率测试仪、WT-2000型少子寿命测试仪对纯度为4N的直拉单晶硅和定向凝固多晶硅的电学性能进行评价；通过电感耦合等离子发射光谱仪(ICP-MS)、金相显微镜、扫描电镜(SEM)、电子探针(EPMA)等实验手段,评价了单晶硅和多晶硅锭的杂质分布和缺陷形态。分析纯度为4N的晶体硅中缺陷和杂质对电学性能的影响,并通过热处理的方式探寻改善电性能的方法。主要得出以下结论：(1)直拉单晶硅中,硅片Ⅰ的杂质含量低,缺陷少,少子寿命较高,为0.674μs。硅片Ⅱ的杂质含量最高,缺陷也大量出现,少子寿命的平均值仅为0.386μs左右。硅片Ⅲ处于两者之间。单晶硅电阻率在0.05Ω·cm左右。(2)多晶硅定向凝固提纯后纯度达到4N,少子寿命平均值为1.286μs：电阻率介于0.2-0.4Ω·cm之间。少子寿命及电阻率的分布与晶界、夹杂、杂质的分布具有相关性。(3)为了提高晶体硅的电学性能,进行热处理实验,结论如下：(a)200℃和450℃低温热处理后,多晶硅少子寿命和电阻率都有所提高。(b)800℃热处理4小时之后,单晶硅和多晶硅的少子寿命均达到最大值。由于高密度晶界和位错的存在,多晶硅的少子寿命提高幅度比单晶硅大。单晶硅电阻率并无变化,而多晶硅电阻率在800℃4h达到1.09Ω·cm。(c)使用多步热处理方法处理晶体硅,选用1150℃作为氧的外扩散温度,800℃作为氧形核温度,1050℃作为氧沉淀长大的温度。研究不同的氧形核时间(2h,4h,6h,8h)对于晶体硅少子寿命的影响。其中对于单晶硅,经过8h的形核时间少子寿命提高的效果最好,处理后达到1.692μs。而多晶硅的形核时间16h最好,热处理后少子寿命达到2.614μs。多步热处理对单晶硅电阻率没有作用,而使多晶硅电阻率提高到1.61Ω·cm。更多还原

【Abstract】 Except for the impurity demand, the electrical property is one of the most important parameters for solar cell. As well known, the impurities and defects will affect the stability of electrical properties and the parameter of device. Silicon solar cells are divided into three types: single crystalline silicon solar cells, multi-crystalline silicon solar cells and amorphous silicon solar cells. Without the influence of grain boundary, the electrical properties of single crystalline silicon solar cells are much steady and the conversion efficiency is higher than multi-crystalline silicon solar cells. But high cost limits its application. For the multi-crystalline silicon films, although the cost is lower, it has a variety of defects, such as grain boundaries (GB), dislocation, micro-defects and impurities in materials (especially the transition-metal impurities); these are all the important factors impacting on the conversion efficiency of multi-crystalline solar cell Due to the diversity types of impurities and defects, the multi-crystalline silicon is lack of systematic research.So far, impurities and defects in electronic grade silicon material have been clear studied, influence of impurities and defects on the electrical properties in relatively low purity (4N-6N) of the silicon material is not clear. Therefore, study on defects and impurities in crystal silicon, and their influence on the electrical properties has great significance.In this paper, using the four point resistivity test system and WT-2000μ-PCD lifetime test machine to character the electrical properties of the single crystal silicon and the multicrystalline silicon. On the other hand, we evaluated the distribution of impurities and morphology of defects in crystalline silicon ingot by inductively coupled plasma emission spectrometry (ICP-MS), optical microscope, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and other experimental methods. In the fifth chapter of the paper, we discussed the influence of heat treatment on the electrical properties.The conclusions as followed:(1) In single crystalline silicon, impurities and defects have a significant influence on the distribution of minority carrier lifetime. In the top part, less impurities and defects make the lifetime higher than other parts, about 0.674μs; the lifetime of middle part is lowest, about 0.368μs.the resistivity is too low to be used, about 0.05Ω·cm (2) The lifetime of the multi-crystalline silicon is 1.286μs,the resistivity is between 0.2 and 0.4Ω·cm. The electrical prosperity is relevant to grain boundaries, inclusions, impurities.(3) Results of heat treatment: (a) After the heat treatment of 200℃and 450℃, minority carrier lifetime and resistivity increased, uniformity is observed. (b) For the 800℃heat treatment of multi-crystalline and single crystalline silicon, the lifetime reach the highest when the time is 2h, because of the existence of high density of grain boundary and dislocation, the lifetime of multi-crystalline has larger margin of increase than single crystalline silicon (c) After the heat treatment 1150℃2h+800℃8h+1050℃8h,the single crystal has the highest lifetime, indicate that the best nucleated time is 8h;for the multi-crystalline silicon, the time is 16h.更多还原