Luminescence techniques, both electroluminescence (EL) and photoluminescence (PL), are becoming powerful tools for inspecting solar cells and photovoltaic modules, 1-7 based on the reciprocity relation between photovoltaic quantum efficiency and luminescence emission. 8,9 EL consists of luminescence emission by solar cells under forward bias, 10 thereby spatially resolving defects that affect the performance and/or durability of the modules, such as cracks, heterogeneous cell activity, failed soldering, grid defects, and dark areas in cells associated with dislocation clusters. 11-18 In contrast, PL consists of luminescence emission under excitation with light. 19-28 The difficulty involved in obtaining a uniform large-area light excitation source over the module surface has prevented it from being applied to module inspection. This problem was circumvented by using the sun as the excitation source, without having to resort to an artificial light source, for example, a laser. 19,29 PL emission depends on the quality of the material, its defects, for example, dislocations, precipitates, and cracks,

Upgraded metallurgical-grade silicon (UMG Si) solar cells with different ranges of efficiencies were characterized through electroluminescence imaging (ELi) and light-beam induced current (LBIC) measurements. The results showed a good correlation between the EL intensity and the efficiency of the solar cells. ELi images gave a bright contrast at the defects, grain boundaries and intragrain defects, and dark contrast inside the grain bodies. Metallic impurities are much more present in some cells due to the directional solidification of the Si ingot. Local short-circuit current mapping with LBIC measurements revealed a bright zone in the neighborhoods of the defects due to the depletion of impurities. Internal quantum efficiencies (IQE) and effective diffusion lengths (Leff) were calculated using different excitation wavelengths. High resolution LBIC measurements revealed micrometric clusters of impurities around intragrain defects.

Today's photovoltaic market is dominated by multicrystalline silicon (mc-Si) based solar cells with around 70% of worldwide production. In order to improve the quality of the Si material, a proper characterization of the electrical activity in mc-Si solar cells is essential. A full-wafer characterization technique such as photoluminescence imaging (PLi) provides a fast inspection of the wafer defects, though at the expense of the spatial resolution. On the other hand, a study of the defects at a microscopic scale can be achieved through the light-beam induced current technique. The combination of these macroscopic and microscopic resolution techniques allows a detailed study of the electrical activity of defects in mc-Si solar cells. In this work, upgraded metallurgicalgrade Si solar cells are studied using these two techniques.

Upgraded metallurgical-grade silicon (UMG Si) solar cells with different ranges of efficiencies are characterized by light-beam induced current (LBIC) measurements. The interaction between grain boundaries (GBs) and metallic impurities is studied for cells fabricated on wafers at different solidification heights of the ingot. One observes a tight relation between the electrical activity of the grain boundaries and the position of the wafer in the ingot, which is related to the impurity contamination. The presence of a high amount of metallic impurities activates the electrical activity of the grain boundaries. The main features of the LBIC images are discussed in relation to the presence of the metallic impurities.