Although crystalline silicon (c-Si) technology has the dominant share in the PV market, its cost must be reduced significantly in order to accelerate the deployment of PV systems.
The team conducts comprehensive research using a semi-production line from ingot slicing to module fabrication and testing.
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Thin wafer fabrication technology
The team is developing a slicing technology for thinner wafers with a thickness of about 0.10 mm (from the present cell thickness of 0.18 mm to 0.08‒0.10 mm).
The team is also investigating the relationship between cracks and wafer strength to develop thin and tough wafers and to improve the yield during cell processes such as wafer cleaning.
Silicon ingot (left) and appearance after slicing (right)
(wafer thickness: 0.12mm)
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Development of new cell fabrication techniques
New cell production processes using the ion implantation technique have been developed in addition to the conventional thermal diffusion process. The effective use of ion implantation can reduce the number of cell processes during back-contact cell fabrication.
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Improvement in module reliability and development of a new evaluation method
A new nondestructive module evaluation method through voltage mapping using the absolute electroluminescence (EL) method has been developed. A forward bias is applied to the solar cell and individual cell voltages can be evaluated based on the luminescence intensity of the cells.
Voltage mapping using the absolute electroluminescence method
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Next-generation multi-junction solar cell“smart stack technology”
The “smart stack technology” using metal nanoparticle arrays has been developed, making the interconnection of various solar cells with different materials and bandgaps possible for the first time. This provides flexibility in material choice and device design because the mismatch in lattice constants, thermal expansion coefficients, etc. can be disregarded with this technique.
Smart stack technology
A GaAs/InP-based four-junction solar cell has achieved conversion efficiency as high as 31.6%, and a GaAs/CIGS-based three-junction solar cell has achieved conversion efficiency as high as 24.2% (joint research with the Research Center for Photovoltaics at AIST Tsukuba Center). We are working to improve and establish this technology for mass production.
The use of thin crystalline silicon as a bottom cell provides high efficiency and low-cost multi-junction cells. The team is developing crystalline silicon based smart stack cells that go beyond the theoretical efficiency limit of single-junction crystalline silicon solar cells (29%). A demonstration GaAs/Si three-junction cell with conversion efficiency of 24.7% has been successfully fabricated.
GaAs/Si-based three-junction smart stack cell