On the impact of twinning on the formation of the grain structure of multi-crystalline silicon for photovoltaic applications during directional solidification

Abstract

International audienceGrain orientation and competition during growth has been analyzed in directionally solidified multi-crystalline silicon samples. In situ and real-time characterization of the evolution of the grain structure during growth has been performed using synchrotron X-ray imaging techniques (radiography and topography). In addition, Electron Backscattered Diffraction has been used to reveal the crystalline orientations of the grains and the twin relationships. New grains formed during growth have two main origins: random nucleation and twinning. It is demonstrated that the solidified samples are dominated by ∑3 twin boundaries showing that twinning on {111} facets is the dominant phenomenon. Moreover, thanks to the in situ characterization of the growth, it is shown that twins nucleate on {111} facets located at the sides of the sample and at grain boundary grooves. The occurrence of multiple ∑3 twins during growth prevents the initial grains from developing all along the sample, and twin boundaries with higher order coincidence site lattices can form at the encounter of two grains in twin position. The grain competition phenomenon following nucleation and twinning acts as a grain selection mechanism leading to the final grain structure

In situ investigation of the structural defect generation and evolution during the directional solidification of 〈110〉 seeded growth Si

“…Two elongated grains grow on each sides (Fig. 2) while no grain competition occurs between them, as already observed previously [28]. It is believed that this is due to the fact that those grains have the same crystallographic orientation 〈110〉 along the growth direction (x) (Fig.…”

“…The dynamic information obtained from the in situ imaging proves that higher order twin grain boundaries, S9 〈110〉 are formed at the encounter of two grains that previously nucleated with a S3 〈111〉 relation on the same grain. S27a 〈110〉 grain boundaries are formed between two grains that are in a S3 〈111〉 twin relation with other grains [28]. All the horizontal and diagonal twin boundaries initiating at the edge of the sample are a S3 〈111〉 type.…”

In Situ Imaging of Dislocation Expansion in FZ‐Si Seeds During Temperature Ramp Heating Process

“…A detailed description of the whole equipment and the previously obtained results can be found in refs. .…”

{1 1 1} facet growth laws and grain competition during silicon crystallization

“…A more detailed description of the whole equipment, of the imaging techniques, of the image processing and of the previously obtained results can be found elsewhere [7,11].…”

“…It is essential to study the groove dynamics as it is directly linked to the grain competition [10] because of its interdependence with the grain boundary orientation relatively to the solidified direction [11].…”