Mono-silicon crystal growth technique lowers solar sell costs

January 19, 2016 // By Paul Buckley
A Japanese research team has developed a new method to grow high-quality mono silicon for solar cells at lower costs.

The researchers, which are led by Takashi Sekiguchi, a leader of the Nano Device Characterization Group, Nano-Electronic Materials Unit, International Center for
Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), and Koichi Kakimoto, a professor at the Research Institute for Applied Mechanics, Kyushu University, have invented a new casting method called a single-seed cast method which is claimed to improve the quality of crystals created compared to conventional casting methods and lead to the development of more efficient silicon solar cells.

As the current conversion efficiency of mainstream silicon-type solar cells has already reached 20%, it is required in future development to increase conversion
efficiency even more to add higher value to the cell products. However, the goal is not achievable using conventionally cast polycrystalline silicon. In addition,

there is demand for the development of a new silicon material to replace polycrystalline silicon and single-crystal silicon for semiconductors, because dislocation-free single crystal silicon for semiconductors is not adequately competitive pricewise.

To address this issue, the research team developed a single-seed cast method, a new silicon casting method using a seed crystal, and succeeded in growing a high-
quality single-crystal silicon (mono silicon) ingot with low impurity. In the new casting method, silicon is melted in a crucible, and a single crystal is grown from a
small seed crystal. This method is less expensive than the method to create single crystal silicon for semiconductors due to reduced raw material use and manufacturing costs. Moreover, the conversion efficiency of a solar cell prototype created using the crystal grown by this method was as high as 18.7%. The efficiency was close to the efficiency of dislocation-free single-crystal silicon (Czochralski (Cz) silicon) wafers for semiconductors (18.9%), which were evaluated concurrently. In future studies, the conversion efficiency of mono silicon may exceed that of Cz silicon by further reducing crystal defects and the impact of impurities.