microstructure Development of multicrystal silicon ingot for solar battery by the control of twinning

为了提高定向凝固太阳电池的光电转换效率和生产率，研究了多晶硅的柱状组织生长机理和缠绕对组织形成的影响。利用布里奇曼式熔化炉在Ar气氛中以0.075~9.6 mm/min的速度和20K/cm的温度梯度，在内径20 mm、高度100 mm的石英坩埚中凝固了太阳能电池级高纯硅晶体。在Ar气氛中，观察到平行于热流方向的柱状组织。在较低的凝固速度下，可以得到较大尺寸的晶粒。孪晶界沿热流方向平行生长，晶面取向关系为Sigma 3。因此，用&lt；111&gt；和&lt；101&gt；和孪晶引入的&lt；211&gt；晶体的晶种测量了生长的过冷度。&lt；111&gt；的过冷度较大，为2.5~5.5K，而&lt；101&gt；的过冷度较小。然而，引入孪晶的&lt；211&gt；样品的过冷度最低，为0.5~3.5K。由于分子动力学模拟还表明，引入孪晶的&lt；211&gt；晶体的凝固速度较快，孪晶界的凹角处形成扭结位置，有利于多面体的生长和晶粒尺寸的长大，硅晶体沿&lt；211&gt；到&lt；101&gt；的取向生长到炉底。随着过冷度的增加和初凝区较快的凝固速度(0.6~2.4 mm/min)的增大，晶粒度增大。然而，为了继续保持如此大的增益尺寸，有必要将速度降低到0.12~0.3 mm/min，直到中末期凝固阶段。

The mechanisms of columnar structure growth of the multicrystal silicon and influence of twining on the microstructure formation are investigated to the development of the photoelectric transformation efficiency and the productivity of solar battery cell fabricated by the unidirectional solidification technique.The solar battery-grade high-purity silicon crystals has been solidified in quartz crucibles, whose inside diameter is 20 mm and the height is 100 mm, at the velocity of 0.075 to 9.6 mm/s and a temperature gradient of 20K/cm by using the Bridgman type furnace at the Ar atmosphere.The columnar structures are observed parallel to the heat flow direction in a velocity about 1.2 mm/min, and the larger size grains are obtained at the lower solidification speed. Twin boundaries, which have the crystal orientation relationship of sigma 3, grow parallel to the heat flow direction. Therefore, the undercoolings for the growth were measured by using seeds of <111> and <101> and twin introduced <211> crystals. The <111> specimens has larger undercooling of 2.5〜5.5K and <101> has smaller. However, twin introduced <211> specimens has lowest undercooling of 0.5〜3.5K. Since it is also revealed that the solidification velocity of twin introduced <211> crystal is higher by the molecular dynamics simulation, the reentrant corner of twin boundary becomes kink site and can give an advantage to the faceted growth and the development of grain size.The silicon crystal grows to the orientation between <211> to <101> along to the crucible bottom. And the grain size was enlarged by increasing the undercooling as well as the faster solidification velocity of 0.6 to 2.4mm/min in the initial solidification region. However, in order to continue such large gain size, it is necessary to reduce the velocity to 0.12 to 0.3mm/min until middle and final solidification stage.