Daisuke Adachi

Impact of carrier recombination on fill factor for large area heterojunction crystalline silicon solar cell with 25.1% efficiency

We have achieved a certified 25.1% conversion efficiency in a large area (151.9 cm2) heterojunction (HJ) crystalline Si (c-Si) solar cell with amorphous Si (a-Si) passivation layer. This efficiency is a world record in a both-side-contacted c-Si solar cell. Our high efficiency HJ c-Si solar cells are investigated from the standpoint of the effective minority carrier lifetime (τe), and the impact of τe on fill factor (FF) is discussed. The τe measurements of our high efficiency HJ c-Si solar cells reveal that τe at an injection level corresponding to an operation point of maximum power is dominated by the carrier recombination at the a-Si/c-Si interface. By optimization of the process conditions, the carrier recombination at the a-Si/c-Si interface is reduced, which leads to an improvement of the FF by an absolute value of 2.7%, and a conversion efficiency of 25.1% has been achieved. These results indicate that the reduction of carrier recombination centers at the a-Si/c-Si interface should be one of the m...

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%.

6 inch High efficiency back contact crystalline Si solar cell applying heterojunction and thinfilm technology

We have developed a 6 inch heterojunction interdigitated back contact (HJBC) solar crystalline Si cell by applying our heterojunction technology and thinfilm technology. To form rear junction and front side passivation, we applied our heterojunction technology that allows efficiency of 24.5% with top/rear contact heterojunction solar cell. To secure this high quality passivation during the HJBC solar cell fabrication process, we have developed deposition technology of insulator layer originally used in thinfilm silicon solar cells. Furthermore, new structure has been designed to drastically suppress the rear electrode resistance. By adapting all these technologies, our HJBC solar cell has reached conversion efficiency of 24.91% independently confirmed at AIST (VOC=737 mV, ISC=10.07 A, FF=80.2 %, PMAX=5.95 W) under 1 sun illumination by total area measurement (239.0 cm2).