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Luis Sanchez1 Miguel Guada1 Angel Moreton1 Sofia Rodriguez Conde1 Oscar Martinez1 Miguel Gonzalez1 Juan Jimenez1

1, University of Valladolid, Valladolid, , Spain

The photovoltaic market is currently dominated by multicystalline silicon (mc-Si) based solar cells with around 70% of total production. Upgrade metallurgical-grade (UMG) Si material, using metallurgical processes for purification of standard-quality silicon metal, suffer from a high dopant level which limits its application. However, UMG Si is demonstrating astonishing progress and hold the promises of lower cost than traditional Siemens proceess, being categorized as an emerging technology. In order to improve the quality of the UMG Si material, it is essential to have a deeper knowledge of the type of defects and their detrimental effects on the photovoltaic conversion. There are several techniques that allow to characterize the electrical activity in solar cells. On the one hand, full-wafer characterization techniques like electroluminescence and photoluminescence imaging (ELi/PLi) provide a fast inspection of the defects at the expense of high spatial resolution. On the other hand, high spatial characterization of solar cells can be achieved using the light-beam induced current (LBIC), but measurements can take many hours. Here we present the study of the electrical activity in UMG mc-Si solar cells using homemade ELi/PLi and LBIC systems.. Several solar cells with well established efficiencies (from 15 to 18 %) have been characterized. The ELi/PLi allow for a fast inspection of the solar cells. The images show dark lines that mainly correspond to grain boundaries and intragrain defects. The histogram level of the images correlates fairly well with the efficiency. In order to obtain a deeper knowledge of the kind of defects and their detrimental effect, high resolution LBIC maps are recorded on selected cell regions, revealing detailed information about intragrain defects, presenting low electrical activity along the core of the defects and high captures rates around them.

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