Antoine Autruffe

High-Performance and Traditional Multicrystalline Silicon: Comparing Gettering Responses and Lifetime-Limiting Defects

In recent years, high-performance multicrystalline silicon (HPMC-Si) has emerged as an attractive alternative to traditional ingot-based multicrystalline silicon (mc-Si), with a similar cost structure but improved cell performance. Herein, we evaluate the gettering response of traditional mc-Si and HPMC-Si. Microanalytical techniques demonstrate that HPMC-Si and mc-Si share similar lifetime-limiting defect types but have different relative concentrations and distributions. HPMC-Si shows a substantial lifetime improvement after P-gettering compared with mc-Si, chiefly because of lower area fraction of dislocation-rich clusters. In both materials, the dislocation clusters and grain boundaries were associated with relatively higher interstitial iron point-defect concentrations after diffusion, which is suggestive of dissolving metal-impurity precipitates. The relatively fewer dislocation clusters in HPMC-Si are shown to exhibit similar characteristics to those found in mc-Si. Given similar governing principles, a proxy to determine relative recombination activity of dislocation clusters developed for mc-Si is successfully transferred to HPMC-Si. The lifetime in the remainder of HPMC-Si material is found to be limited by grain-boundary recombination. To reduce the recombination activity of grain boundaries in HPMC-Si, coordinated impurity control during growth, gettering, and passivation must be developed.

High performance multicrystalline silicon: Grain structure and iron precipitation

A study of the spatial occurrence of iron precipitation in a high performance multicrystalline silicon (HPMC-Si) sample is presented. The separated effects of grain-boundaries, sparse intra-granular dislocations, and dislocation clusters are investigated by combining the Fei imaging method with glow discharge mass spectroscopy, electron backscatter diffraction, and two iron precipitation models. While the area-averaged precipitation at grain boundaries is relatively minor, almost the whole iron precipitation occurs within the grains, despite the very low intra-granular dislocation density. The fraction of non-precipitated iron in the studied HPMC-Si material was found to be one to two orders of magnitude higher than that reported previously for standard materials.

Identification of Grain Boundary Segregation Mechanisms during Silicon Bi-Crystal Solidification

Small angle grain boundaries have been grown in a small Bridgman furnace, using seeded growth method, at three different pulling rates i.e. 3 μm/s, 13 μm/s and 40 μm/s. In order to assess segregation mechanisms of impurities towards the central grain boundary, melt has been polluted by 50ppma of either copper or indium. Secondary ion mass spectrometry (SIMS) local analyses have been performed to investigate the impact of solid state diffusion and limited rejection of solute at the grain boundary for each growth rate. The results are discussed in connection with an atomistic model built on Vienna Ab-initio Simulation Package (VASP).