Twinning in multicrystalline silicon for solar cells

• Evolution of twins in multicrystalline silicon was studied on as cut wafers.
• Twins are classified as ribbon twins, polygon twins or needle twins.
• Twins appear to nucleate in grain boundary junctions or at macroscopic facets on grain boundaries.
• Grain boundary type was studied by electron backscatter diffraction (EBSD) and pole figure analysis.
• Minimization of grain boundary energy is suggested as the mechanism responsible for the observed twinning events.

Twinning in multicrystalline silicon was studied by observing the surface of as-cut wafers and by EBSD. By tracing twin structures downwards to their first point of origin, the conditions at the point of generation were identified. Twins covering the whole width of a grain predominantly originates at junctions between three grain boundaries. Twins also originate at straight grain boundary segments of alternating direction, indicative of faceted grain boundaries. The phenomena are proposed to occur because they reduce grain boundary energy, which is substantiated by pole figure analysis. In addition to the CSL relationship, the orientation of the grain boundary in low energy configurations turned out to be essential.