Interactions Between Metals and Different Grain Boundary Types and Their Impact on Multicrystalline Silicon Device Performance

The mechanical and electrical properties of polycrystalline solids, such as metals, ceramics, and photovoltaic-grade multicrystalline silicon (mc-Si), are strongly regulated by the interactions between impurities and grain boundaries. In this broader context, we combine synchrotron-based X-ray fluorescence microscopy (λ-XRF), SEM-based electron back-scatter diffraction (EBSD), and conventional techniques to correlate metal precipitation behavior with grain boundary character (type), electrical activity, and microstructure in commercial multicrystalline silicon (mc-Si) materials. It is directly observed that metals tend to form precipitates selectively at higher-Σ coincidence site lattice (CSL) boundaries and non-CSL boundaries, while largely avoiding precipitation at Σ3 boundaries, and to a lesser extent, Σ9. The electrical impacts of this behavior differ, depending on surrounding intragranular quality. A discussion of mc-Si grain boundary engineering ensues.