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Neutron Activation Analyses (NAA) Investigation of Transition-Metal Impurities Contents in Solar-Grade Silicon Feedstock for Directional Solidification of Photovoltaic HEM Silicon Ingot
Y. Chettat, L. Hamidatou, M. Salhi, H. Slamene, A. Lami, A. Benmounah
HEM, Transition Metals, Growth, Silicon Ingot, Solar Grade Silicon Feedstock, Multicrystalline Silicon Wafer
Wafer-Based Silicon Solar Cells and Materials Technology
Subtopic: Silicon Feedstock, Crystallisation and Wafering
Event: 32nd European Photovoltaic Solar Energy Conference and Exhibition
Session: 2DV.3.3
996 - 1000
ISBN: 3-936338-41-8
Paper DOI: 10.4229/EUPVSEC20162016-2DV.3.3
0,00 EUR
Document(s): paper, poster


The degradation of multicrystalline silicon (mc-Si) Lifetime is mainly caused by defects such as: precipitates, inclusions, dislocations and transition-metals impurities simply known by traps or lifetime killers. The main source of theses contaminants are diffusion from solar silica crucible, silicon nitride coating and solar grade silicon feedstock starting material. Some impurities such Ta, W, V, Nb and Fe are very dangerous and can degrade the efficiency of the silicon solar cell at very low concentrations. Therefore, a strict control of the silicon feedstock material specifications via using very high sensitive analytical technique for traces and ultra-traces analyses is more than necessary. In this work we have used an advanced high sensitivity and multi elementary analytical technique such Neutron Activation Analyses (NAA) which require no chemicals treatment for sample preparation in attempt to determine exactly which transition-metal impurities and with which concentrations they are present in three different batch samples of solar grade silicon feedstock supplied by Silicon Recycling Services (SRS) supplier, and three other different standards mc-Si wafers from the edge of the silicon ingot obtained by HEM crystallization of thereof solar grade silicon feedstock. We have used also a lifetime tester type Sinton WCT-120 in mode QSSPC to investigate the electrical quality of the heart of the silicon ingot. The obtained results show that silicon feedstock material and mc-Si ingot (wafers) are heavily contaminated by transition and alkaline metals impurities. The main dominates metallic impurities found in the silicon feedstock material are : Mo, Nd, Zr, W, Cr, Fe, Co, Zn, Au, Sc, Ce, La, Th, Rb, and Ba, Ca, Na, K with concentrations exceeding thousand-folds theirsholds concentrations in silicon feedstock material, and the dominates metallic impurities found in mc-Si wafers are: W, Fe, Cr, Co, Ag, Sc, Ce, La, Hf with concentrations exceeding hundred-folds their-sholds in mc-Si type P for photovoltaic application, and that the lifetime seems to be remarkably degraded with only 4,8 μs max in the heart of the ingot. This degradation is mainly caused by the intense transition metal-contamination of silicon feedstock material.