Coincident site lattice bi-crystals growth—Impurity segregation towards grain boundaries

Lattice distortion induced site dependent carbon gettering at twin boundaries in silicon

“…C, O, N, etc. ), most of which have detrimental effect on the solar cell efficiency [4,5,[7][8][9]. C, usually inherited from crucible and furnace during casting process, is an inevitable impurity in mc-Si.…”

X-ray Based in Situ Investigation of Silicon Growth Mechanism Dynamics—Application to Grain and Defect Formation

“…However, cm-Si efficiencies are still limited due to the presence of structural defects such as parasitic grain nucleation on the walls of the crucible [4,7], twin formation and more importantly, dislocations. The latter can be either arranged in cellular patterns, in the entire cm-Si ingot and are known as background dislocations [8] or generated on the top of the seeds [9,10], at their junctions on precipitates [10] and propagate vertically along the growth direction [9,[11][12][13][14][15][16] generating the formation of sub-grain boundaries. HP mc-Si technique is based on a very different approach aiming at obtaining small-size and uniform grains at the initial stage of solidification with random angle and coherent grain boundaries [6,17].…”

Effect of grain boundary grooves at the crystal/melt interface on impurity accumulation during the unidirectional growth of multicrystalline silicon

“…Therefore, a fundamental understanding of impurity accumulation during crystallization from the melt is required to control the impurity distribution in the ingot. To date, it has been shown that metallic impurities accumulate at grain boundaries, and the impurity concentration depends on the grain boundary characteristics, as defined by the coincidence site lattice (CSL) indices (Σ parameters) of mc-Si wafers [1][2][3]9]. The concentration of metallic impurities was high at high-Σ grain boundaries and at random grain boundaries not defined by Σ parameters, but low at the Σ3 twin boundary.…”

“…Therefore, impurity accumulation and precipitation phenomena at the grain boundaries were discussed on the basis of atomic diffusivity in the solid phase. However, in the casting process, metallic impurities might accumulate at grain boundaries at the crystal/ melt interface during unidirectional growth because grain boundary grooves are formed at the crystal/melt interface [9,[11][12][13]. In a previous study, we found indications that groove formation at the crystal/melt interface was one cause of impurity accumulation at grain boundaries; however, sufficient supporting evidence was unavailable because we observed a crystal/melt interface of pure Si, which did not include impurity elements [13].…”

“…In the casting of multicrystalline Si (mc-Si) ingots for solar cells, metallic impurities, oxygen, and carbon are incorporated into the ingot from the crucible, which is usually coated with Si 3 N 4 powder, and from the atmosphere [1][2][3][4][5][6][7][8][9]. If low-grade raw materials, also called metallurgical silicon or solar-grade silicon, are used for the growth, a variety of metallic impurities will be present in the melt.…”