Characterizing different defects in multicrystalline silicon solar cells via modern imaging methods

Defects in multicrystalline silicon solar cells such as impurities, gain boundaries, dislocations and metallic impurities have great influence to the final conversion efficiency of devices. Moreover, different kinds of defects and defects at different depth layers in multicrystalline silicon solar cell play different roles to the final performance of devices. This paper proposes a fast technique via electroluminescence imaging method to distinguish different types and depths defects. Different types of defects have various influences to the distribution of extra minority carriers which would result in the distinctions in the final luminescence spectrum and intensity. Therefore, we can recognize these defects via a group of EL images in a few seconds. Also, we found that defects at different depths show a closely relationship with electrical breakdown which would lead to the differences on the final electroluminescence properties. The EL images under different forward-biased and reversed-biased voltages give a clear separation of defects near the front surface, around p-n junction and in bulk material. Light beam induced current (LBIC) imaging is used to verify the methods we proposed. These modern imaging methods could become popular methods in photovoltaic testing field, and we hope our research could give some help in the study of silicon based devices.