Integrated imaging in three dimensions: Providing a new lens on grain boundaries, particles, and their correlations in polycrystalline silicon

Most technologically-relevant materials exhibit a microstructural heterogeneity over multiple length scales, and it is this heterogeneity that ultimately determines their performance. For example, the efficiency of polycrystalline silicon (poly-Si) photovoltaic cells is critically dependent on the nature of the grain boundaries and foreign metal impurities in the bulk. Here, we probe the characteristics and distributions of these defects in three dimensions by using a novel, integrated, and non-destructive imaging platform. In particular, recent advances in laboratory-based diffraction contrast tomography (LabDCT) enable us to measure grain centroid, volume, orientation, and shape. From this crystallographic information, we extract the five-parameter grain boundary distributions in poly-Si. By using a combination of LabDCT, attenuation-based tomography, and electron microscopy, we determine that the location of the impurity particles is non-random in the bulk and strongly dependent on grain boundary character. The correlative analysis not only demonstrates the degree of interaction between foreign metal impurities and structural defects in poly-Si, but also highlights the viability of burgeoning tomographic methods such as LabDCT. It is anticipated that our integrated approach can be extended to other complex microstructures with minimal sample-specific tuning. (c) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.