Thomas Pernau

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 (mu-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-Sigma coincidence site lattice (CSL) boundaries and non-CSL boundaries, while largely avoiding precipitation at Sigma3 boundaries, and to a lesser extent, Sigma9. The electrical impacts of this behavior differ, depending on surrounding intragranular quality. A discussion of mc-Si grain boundary engineering ensues