High-quality industrial n-type silicon wafers with an efficiency of over 23% for Si heterojunction solar cells

Abstract

n-type CZ-Si wafers featuring longer minority carrier lifetime and higher tolerance of certain metal contamination can offer one of the best Si-based solar cells. In this study, Si heterojuction (SHJ) solar cells which was fabricated with different wafers in the top, middle and tail positions of the ingot, exhibited a stable high efficiency of>22% in spite of the various profiles of the resistivity and lifetime, which demonstrated the high material utilization of n-type ingot. In addition, for effectively converting the sunlight into electrical power, the pyramid size, pyramid density and roughness of surface of the Cz-Si wafer were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). Furthermore, the dependence of SHJ solar cell open-circuit voltage on the surface topography was discussed, which indicated that the uniformity of surface pyramid helps to improve the open-circuit voltage and conversion efficiency. Moreover, the simulation revealed that the highest efficiency of the SHJ solar cell could be achieved by the wafer with a thickness of 100 µm. Fortunately, over 23% of the conversion efficiency of the SHJ solar cell with a wafer thickness of 100 µm was obtained based on the systematic optimization of cell fabrication process in the pilot production line. Evidently, the large availability of both n-type ingot and thinner wafer strongly supported the lower cost fabrication of high efficiency SHJ solar cell.

Keywords

n-type Cz-Si / thinner wafer / surface texture / high efficiency / SHJ solar cell

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Acknowledgments

This work was supported in part by the National High Technology Research and Development Program of China (863 Program, Grant No. 2011AA050501), the Main Program of Knowledge Innovation of Chinese Academy of Sciences (Grant No. KGCX2-YW-399þ11), the International S&T Cooperation Program of China (Grant No. 2015DFA60570), and the Key Project of Zhangjiang National Innovation Demonstration Zone Special Development Fund (Grant No. ZJ2015-ZD- 001). The n-type silicon wafers in this study were partly supported by Xi’an Longi Silicon Materials Corp.

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2016 Higher Education Press and Springer-Verlag Berlin Heidelberg