By using an EL detector to detect battery cells, we studied two abnormal battery cells that exhibit severe reverse linear leakage in electrical performance, namely "black wire" battery cells and point burn through battery cells. By comparing and observing the microstructure of the surface and cleavage section of the abnormal location, we found that the essential reason for the occurrence of these two reverse leakage phenomena is due to the presence of dislocations or other crystal defects in the silicon wafer structure at their location. This reverse leakage phenomenon caused by crystal defects can cause local overheating of the battery during operation, posing a huge risk to the photovoltaic power generation system.

Randomly selected 10 "black wire" battery cells for electrical performance testing, and tested the current of the "black wire" cells as a function of reverse load voltage,. It can be seen that the current of these "black wire" samples shows a linear relationship with the reverse load voltage, indicating a relatively serious linear leakage, indicating the presence of emitter or body region inversion, impurities, or some defects penetrating the battery in this type of sample.

Dislocations and other defect structures in silicon crystals can lead to incomplete crystal structure and become attachment points for harmful metals and impurities, which can easily accumulate in the defect areas of the crystal. After the subsequent preparation into a battery, especially if the metal impurities are deep level impurities, it will lead to a decrease in the reverse breakdown voltage of the junction, an increase in leakage loss, resulting in a large PN junction leakage current, and even directly causing the PN junction to narrow. In addition, this structure will become a very serious carrier recombination center, generating leakage current during the movement of carriers towards the recombination center. Due to the strong recombination effect of the structure on charge carriers and the local failure of the PN junction, the power generation capacity of this region is extremely weak. If solar cells are simplified into countless micro cells connected, the areas with crystal defects become loads in the entire system due to their negligible power generation capacity. The currents generated by other micro cells supply power to them, causing leakage. At the same time, the high resistance of the crystal defect areas releases a large amount of heat, causing local overheating. When this type of "black wire" is connected to a photovoltaic power generation system, the weak power generation capacity in the area will cause it to be in a reverse bias state in the system. When the reverse bias voltage is large enough, it will cause avalanche breakdown, resulting in a large amount of local heat release and the formation of "hot spots". Meanwhile, prolonged localized high temperatures can lead to the failure of the entire battery cell, ultimately causing component damage and even posing a risk of fire in cases of poor heat dissipation.

The images we obtained through EL testing can clearly show the presence of hot spots, which can pose a huge risk to photovoltaic power generation systems. The EL detector can easily detect internal problems of various solar cells and help solve photovoltaic problems.

LAILX is committed to the research and production of photovoltaic testing equipment, including EL testing series, portable EL detectors, string EL detectors, drone EL testers, IV power testing series, portable IV testers, power quality analyzers, and other related photovoltaic power station testing equipment and photovoltaic production line laboratory testing equipment.