太阳电池用晶体硅中金属杂质与缺陷的相互作用研究

发布时间：2018-01-28 12:30

本文关键词： 多晶硅太阳电池金属杂质晶界位错磷吸杂氢钝化　出处：《浙江大学》2014年博士论文　论文类型：学位论文

【摘要】：光伏发电是近年来发展最快的可再生能源技术之一,而晶体硅太阳电池占据了全球光伏市场90%以上的份额。硅材料尤其是多晶硅材料内的金属杂质和缺陷对于硅片质量及太阳电池的性能影响较大,是学术界和产业界关注的重点和热点问题之一。因此,研究硅中金属杂质与缺陷具有重要的理论意义和实际应用背景,也是适应硅太阳电池低成本、高效率的发展趋势的必然要求。本文在综述前人研究成果的基础上,利用少子寿命测试仪、电流-电压／电容-电压测试仪、光学显微镜等技术,结合铸造多晶硅生产实际中的问题,系统地研究了金属杂质与位错的相互作用、金属杂质与晶界的相互作用及金属杂质对于对硅片和太阳电池电学性能的影响,取得了如下主要的创新成果： (1)研究了铸造多晶硅边缘区域(红边区)低少数载流子寿命的起因及对太阳电池性能的影响。实验发现：来自坩埚与坩埚涂层中间隙铁杂质的扩散是导致边缘区域硅晶体少子寿命降低的主要原因；通过磷扩散吸杂,可以有效减少边缘区域的间隙铁浓度,从而提高该区域的有效载流子寿命；经历太阳电池制备工艺后,含边缘区域的太阳电池片的性能可以得到大幅度改善,仅仅比普通电池片效率略低。 (2)研究了金属杂质对硅中晶界电学性能的影响。阐述了Fe、Cu、Ni、Cr、 Co、Mn几种金属沾污对于(110)/(100)大角晶界的电学性能参数的影响规律。发现：在几种金属沾污后,晶界的能级分布均向深能级范围移动,晶界态密度有不同程度的提高,载流子捕获截面也有所增大,其中Fe杂质对于晶界态密度的影响最大；随着金属沾污含量的增大,导致晶界的能级分布更深、晶界态密度增大；Cu/Ni在共沾污时晶界的缺陷能级分布比Cu与Ni单种金属沾污导致的晶界能级位置更深,晶界态密度略有增大。实验还指出：通过特定条件的热处理,可以降低金属沾污晶界的态密度及载流子捕获截面；通过低温退火调控晶界上金属沉淀的尺寸及密度分布,进而可以调控晶界的电学性能、改善金属沾污晶界的多晶硅器件性能；通过氢钝化,晶界引入的能级分布在更窄的范围,空穴捕获截面也降低了两个数量级左右,晶界态密度略有降低。 (3)研究了位错对晶体硅电池性能的影响。结合普通铸造多晶硅、高效铸造多晶硅以及铸造单晶硅,得到了位错分布对于硅片质量及太阳电池的性能影响。实验发现：高效多晶硅由于具有更低的位错密度,更均匀的晶粒分布,表现出均匀的少子寿命分布,电池效率高于普通多晶硅电池；铸造准单晶硅材料硅锭中间的单晶区域不含有晶界,位错密度较低,硅片性能最好、电池效率最高；而铸造准单晶硅边缘含有多晶和大量的位错聚集体,缺陷密度极高,对少子寿命影响很大、电池效率也最低。实验还说明：位错密度与位错分布的均匀性对于硅材料的质量以及太阳电池的性能有着显著地影响,位错密度越高、位错的聚集体越多,电池的效率越低。 (4)研究了硅中金属杂质的磷扩散吸杂效应。实验发现：对于n型硅晶界上的金杂质沾污,磷扩散吸杂可以有效吸杂出晶界处的杂质,但吸杂效率受沾污程度影响；在低浓度沾污下,一步磷吸杂可以有效吸杂出晶界上的金杂质；而在严重沾污下,两步变温磷吸杂更为有效。实验证明：在普通工艺磷扩散样品中,表面死层中会存在SiP沉淀,显著增强载流子的复合及电池性能；增加后续退火以及改变扩磷工艺参数两种方法可以通过消除SiP沉淀有效改善太阳电池的性能。
[Abstract]:Photovoltaic power generation is one of the renewable energy technology rapid development in recent years, while the crystalline silicon solar cells occupy more than 90% share of the global PV market. Especially the influence of polysilicon silicon material in the metal impurities and defects in silicon solar cell performance and quality greatly, is one of the most important and hot issues of concern in academia and industry. Therefore, study on silicon metal impurities and defects has important theoretical significance and practical application background, but also to the silicon solar cell with low cost, high efficiency of the inevitable requirement of the development trend.
Based on the review of previous research results, using the minoritycarrier lifetime tester, current voltage and capacitance voltage tester, optical microscope, combined with the actual production of polysilicon casting problems in the systematic study of the interaction of metal impurities and dislocations, metal impurity and grain boundary interactions and metal impurities the effect of silicon wafer and solar battery electrical performance, achieved the following major innovations:
(1) on the multicrystalline silicon edge region (red border) effect of low minority carrier lifetime and the cause of solar cell performance. The experimental results showed that: the diffusion of iron impurities from the crucible and the crucible coating gap is the main reason leading edge region of the silicon crystal lifetime decreased; the phosphorus diffusion gettering can effectively. To reduce the gap of iron concentration in edge areas, so as to improve the effective carrier lifetime in the region; through the preparation of solar cells, the performance of solar cell slice with edge areas can be improved greatly, only than the ordinary battery efficiency is slightly lower.
(2) to study the effect of metal impurities on the electrical properties of grain boundaries in silicon are expounded. The Fe, Cu, Ni, Cr, Co, Mn for several metal contamination (110) / (100) effects of electrical performance parameters of grain boundary. Found in several kinds of metal contamination, the energy level distribution of grain boundary moving to the deep level range, the grain boundary density have different degrees of increase, the carrier capture cross section is increased, the Fe effect of impurity on the grain boundary density maximum; with the increase of the content of metal contamination, resulting in deeper level distribution of grain, grain density increased; grain boundary level deeper defect level distribution of Cu/Ni in the total contamination at the grain boundary the ratio of Cu and Ni single metal contamination caused by the grain boundary density increased slightly. The experiment also pointed out that: heat treatment by specific conditions, can reduce the density of States and the carrier of metal contamination of grain boundary trapping cross section by low temperature annealing; The size distribution and density of grain boundary precipitation of metal fire control, which can control the electrical properties of grain boundaries, improve the performance of polycrystalline silicon device metal contamination of grain boundaries; through hydrogen passivation, the energy distribution in the grain boundary into a narrower, hole capture cross section was reduced by two orders of magnitude, the grain boundary state density decreased slightly.
(3) studied the effect of dislocation on the performance of crystalline silicon solar cells. The combination of common casting polycrystalline silicon, polysilicon and monocrystalline silicon casting, casting, the dislocation distribution influence on the quality and performance of the silicon solar cell. It was found that the high dislocation density due to polysilicon is lower, the grain distribution is more uniform, showing the minoritycarrier lifetime uniform distribution, the battery efficiency is higher than that of common polysilicon battery; casting single crystal silicon ingot middle region quasi monocrystalline material does not contain grain, lower dislocation density, silicon performance best, battery efficiency is the highest; the casting of quasi monocrystalline polycrystalline and edge contains a large number of dislocation aggregates, defect density is very high, a great impact on the lifetime of the battery. Efficiency is the lowest. The experiment also shows that there is a significant influence of the uniformity of the performance and the dislocation density of the dislocation distribution for quality silicon materials and solar cells The higher the dislocation density, the more the dislocation aggregates, the lower the efficiency of the battery.
(4) the effect of metal impurities in silicon phosphorus diffusion gettering effect. It is found that the gold impurity contamination of N type silicon on grain boundary, phosphorus diffusion gettering can effectively gettering impurities at the grain boundaries, but the gettering efficiency of contaminated degree of influence; in the low concentration of contamination, a step of phosphorus gettering the gold impurity effectively gettering out on grain boundary; in serious contamination, two step temperature of phosphorus gettering is more effective. The experiment proves that in the process of ordinary phosphorus diffusion in the sample, the surface of the dead layer will exist in the SiP precipitation, significantly enhance the performance of the composite and battery carrier; two methods increase and subsequent annealing change the process parameters can be eliminated through the expansion of phosphorus precipitation can effectively improve the performance of SiP solar cells.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM914.4

【相似文献】