Diagnosing breakdown mechanisms in monocrystalline silicon solar cells via electroluminescence imaging

[Display omitted] •Breakdown phenomena were observed in monocrystalline Si solar cell by EL imaging.•Defect-induced breakdown was diagnosed by combining distributed circuit modeling.•Luminescence mechanism of avalanche breakdown was figured out by Si band structure.•Early breakdown was found to be consistent with the Zener effect.•This work provides achievable methods for analyzing solar cell breakdown mechanisms. The local breakdown behavior may be harmful to solar cells and could possibly permanently damage the cell. Therefore, understanding the breakdown mechanisms in commercially competitive photovoltaic devices such as monocrystalline silicon (Si) solar cells is of great importance. Here, by using the reverse-biased electroluminescence (ReBEL) imaging technique, we observed three types of breakdown phenomena in monocrystalline Si solar cells: defect-induced breakdown, avalanche breakdown, and early breakdown. We have applied a variety of methods to diagnose each breakdown mechanism. The positions of defect-induced breakdown were first determined by combining EL and ReBEL imaging. An innovation method, the distributed circuit modeling was further introduced to trace the formation of different defect-induced breakdown sites. It is firstly applied this approach in the analysis of the breakdown mechanism. Then, avalanche breakdown was demonstrated by the temperature coefficient. The origin of its emission spectra was analyzed by the Si energy band structure combined with Baraff theory. Moreover, the characteristic of early breakdown was found to be consistent with the Zener effect, which may be caused by the metal stains such as aluminum (Al) during the manufacturing process.