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High quality, low cost crystals for more efficient solar cells

A research team from Japan, led by Takashi Sekiguchi of the Nano-Electronic Materials Unit, International Centre for Materials Nanoarchitectonics and Koichi Kakimoto, a professor at the Research Institute for Applied Mechanics, Kyushu University, has developed a method to grow high-quality mono silicon at low cost.

The research resulted in a casting method the researchers have called the single-seed cast method. They say it has improved the quality of crystals created compared to conventional casting methods, which could potentially lead to the development of more efficient silicon solar cells.

The current conversion efficiency of mainstream silicon-type solar cells has reached 20%; it is required in future development to increase conversion efficiency to add higher value to the cell products. However, it is said that this goal is not achievable using conventionally cast polycrystalline silicon. In addition, there is demand for the development of a silicon material to replace polycrystalline silicon and single-crystal silicon for semiconductors, as the price of dislocation-free single crystal silicon is not adequately competitive.

The researchers claim that their single-seed cast method has succeeded in growing a high-quality single-crystal silicon (mono silicon) ingot with low impurity. In this casting method, silicon is melted in a crucible, and a single crystal is grown from a small seed crystal. This method is said to be 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%. This is close to the efficiency of dislocation-free single-crystal silicon (Czochralski (Cz) silicon) wafers for semiconductors, which were evaluated concurrently and scored and efficiency of 18.9%. 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.

The researchers say that their technology is compatible with, and can be integrated into existing production lines and can feasibly grow an ingot as large as 50cm3.

Author
Tom Austin-Morgan

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