Naoaki Nakanishi

High Efficiency Silver-Free Heterojunction Silicon Solar Cell

In this work, we present the results of the replacement of silver screen printing on heterojunction crystalline silicon (c-Si) solar cells with a copper metallization scheme that has the potential to reduce the manufacturing cost while improving their performance. We report for the first time silver-free heterojunction c-Si solar cells on 6-in. wafers. The conversion efficiency reached is a record 22.1% for c-Si technology for this wafer size (Voc = 729 mV, Jsc = 38.3 mA/cm2, FF= 79.1%). The total power generated is more than 5 W for 1-sun illumination, which is a world record. Heat-damp reliability tests show comparable performance for mini-modules fabricated with copper metalized as for conventional silver screen printed heterojunction c-Si solar cells.

High-efficiency heterojunction crystalline Si solar cell and optical splitting structure fabricated by applying thin-film Si technology

Thin-film Si technology for solar cells has been developed for over 40 years. Improvements in the conversion efficiency and industrialization of thin-film Si solar cells have been realized through continuous research and development of the thin-film Si technology. The thin-film Si technology covers a wide range of fields such as fundamental understanding of the nature of thin-film Si, cell/module production, simulation, and reliability technologies. These technologies are also significant for solar cells other than the thin-film Si solar cells. Utilizing the highly developed thin-film Si solar cell technology, we have achieved ~24% efficiency heterojunction crystalline Si solar cells using 6-in. wafers and >26% efficiency solar cells with an optical splitting structure. These results indicate that further improvement of thin-film Si technology and its synergy with crystalline Si solar cell technology will enable further improvement of solar cells with efficiencies above 26%.