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Study of Defects and Impurities in Multicrystalline Silicon for Solar Cells

Author: WuShanShan
Tutor: WangLei；YangDeRen
School: Zhejiang University
Course: Materials Physics and Chemistry
Keywords: Casting polysilicon Minority carrier lifetime Fe-B pair Dislocation Battery technology
CLC: TM914.41
Type: Master's thesis
Year: 2011
Downloads: 399
Quote: 0
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Abstract


Casting polysilicon beyond monocrystalline become the most important raw materials of the solar cell because of its having a higher performance and lower cost. Czochralski silicon casting polysilicon contain more impurities and defects, these impurities and defects will significantly reduce silicon minority carrier lifetime. Particularly near the ingot edge of the crucible, the influence of contamination and crystal growth of the crucible thermal field, the crystal quality is poor, low minority carrier lifetime with cutaway side skin, persists. This makes the corners of the ingot application has been limited, reducing the effective utilization of polycrystalline silicon ingot. Polysilicon ingots edge area therefore need to understand the formation of low minority carrier lifetime with the reasons for such low minority carrier lifetime with whether the impact of the final solar cell efficiency obtained by gettering and other technology tools to enhance the value of life, as well as the area of ??low minority carrier lifetime a series of questions. This series of questions and clarify polysilicon corner silicon industrialization has important significance. Firstly, using microwave photoconductivity decay instrument (micro-PCD), inductively coupled plasma mass spectrometry (ICP-MS), Fourier transform infrared spectrometer (FTIR), and optical microscopy (OM) testing methods, different regions of the polysilicon film Characterization of the system. On this basis, focusing on the reasons for the formation of the the ingot edge of the zone of low minority carrier lifetime. Experimental results show that: by the influence of the low minority carrier lifetime region corners average minority carrier lifetime of the silicon is low compared to the intermediate silicon wafer; interstitial oxygen in a low minority carrier lifetime region, alternate position carbon and the remaining concentration of metal impurities and other high lifetime region The concentration of similar, but the content of the Fe-B was significantly higher than in other regions; dislocation density in the low minority carrier lifetime region is significantly lower than its adjacent zone. Therefore, the high concentration of Fe-B pair is the main reason for the low minority carrier lifetime region is formed, and the low dislocation density in the low minority carrier lifetime region is promoted Fe mostly in the form of the Fe-B pair is present in a low minority carrier lifetime region. On this basis, by a conventional battery manufacturing process, the paper made had corner sheet solar cell and the intermediate sheet solar cell. The IV tests showed little difference between the two types of batteries battery performance parameters, the efficiency of about 16% are. And light-induced current (LBIC) test after the battery manufacturing process corners silicon minority carrier diffusion length distribution tends to be uniform, the area of ??the original low minority carrier lifetime disappeared. To further study to enhance the performance of key corners silicon process the papers by P gettering simulated solar cell technology, H passivation and A1 gettering three processes, the three main process area of ??low minority carrier lifetime . The results show: the phosphorus gettering and hydrogen passivation can significantly improve the quality of silicon tends to be uniform, and the quality of materials. In contrast, rapid thermal processing (RTP) expanded Al sample improvement is not obvious. The results show that, with the presence of low minority carrier lifetime of the impact will not have the use of the corner piece. Excellent battery manufacturing process corners silicon can still be used to make efficient batteries. The results of this study can eliminate the concerns of the use of the industry for the corners of silicon wafer, greatly increasing the utilization of the cast polycrystalline silicon ingot, thereby further reducing the production cost of casting polysilicon material.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Photocell > Solar cells > Silicon solar cell
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