Research on the Blackening of EL Images on the Cutting Surfaces of Semi-Module PERC Solar Cells
I. Research Background
In the production of photovoltaic (PV) modules, the blackening or dark spots observed in the electroluminescence (EL) images of PERC (Passivated Emitter and Rear Cell) monocrystalline silicon solar cells is a common quality issue. This phenomenon not only affects the photovoltaic conversion efficiency of the cells but can also lead to a decline in the reliability of the modules. Therefore, studying the causes of EL image blackening and finding solutions is of great significance.
II. Causes of EL Image Blackening
Contamination in the Texturing Machine's Drying Tank
Research indicates that contamination of the drying tank in the texturing machine by NaOH (sodium hydroxide) is one of the main causes of blackening in the EL images of PERC monocrystalline silicon solar cells. During the production process, NaOH may be introduced into the drying tank via steam or liquid, thereby contaminating the surface of the cells.
Abnormalities in the Rear Passivation Layer
The rear passivation layer of PERC cells is highly sensitive to the surface condition of the silicon wafer. If there are abnormalities or contamination between the passivation layer and the silicon wafer, dark spots or black areas may appear in the EL images.
Metallic Impurity Contamination
The formation of dark spots in EL images may also be related to metallic impurity contamination. These impurities can affect the minority carrier lifetime of the cells, manifesting as dark spots in the EL images.
Other Factors
Other factors that may lead to EL image blackening include crystal impurities in the cells, surface precipitation, dust or fingerprints in the testing environment, etc.
III. Solutions
Optimization of Production Processes
Adjust the parameters of the robotic arms to reduce the carryover of alkaline liquids into the drying tank.
Optimize the exhaust system inside the texturing machine to minimize the volatilization of NaOH steam.
Regularly maintain and clean the drying tank.
Improvement of Passivation Processes
Ensure process stability during the deposition of aluminum oxide passivation layers to avoid unevenness in the film formation.
Enhancement of Testing Environment Cleanliness
Maintain a clean testing environment during EL testing to reduce the impact of external factors on the test results.
Implementation of Grayscale Classification
Establish a grayscale classification for cells with lower efficiency and a higher propensity for dark spots to reduce the production of substandard modules.
IV. Research Conclusions
Through research on the blackening of EL images on the cutting surfaces of PERC photovoltaic modules, it has been found that the main causes include contamination of the drying tank in the texturing machine by NaOH, abnormalities in the rear passivation layer, and metallic impurity contamination. By optimizing production processes, improving passivation techniques, and enhancing the cleanliness of the testing environment, the occurrence of EL image blackening can be effectively reduced. This, in turn, improves the yield and reliability of photovoltaic modules.
