Cracking and Recognition Method of Solar Cells
Author: Source: Datetime: 2016-10-11 14:23:52
Due to the crystal structure of its own characteristics, crystalline silicon cells for solar powered portable generator are very prone to rupture. Crystalline silicon components of the production process is long, many links are likely to cause battery cell crack (according to Xi'an Jiaotong University Yang Hong teacher information, only the battery production stage there are about 200 kinds of reasons). The essential cause of crack initiation can be summarized as mechanical stress or thermal stress on the silicon wafer.
In recent years, crystalline silicon component manufacturers in order to reduce costs, crystalline silicon cells have been growing thinner direction, thus reducing the battery to prevent mechanical damage. In 2011, the German ISFH published their findings: according to the shape of the battery cell cracked, can be divided into five categories: tree-like cracks, integrated crack, oblique crack, parallel to the main grid line, perpendicular to the gate line and throughout the Cell sheet cracks.
Effect of Crack on Component Performance
Different cracked, the impact on the cell chip function is not the same. According to the structure of crystalline silicon cells, as shown above, the current generated by the battery to rely on "the surface of the main gate line and perpendicular to the main grid line fine line" collection and export. When the crack causes the fine grid line to break, the fine grid line can not transfer the collected current to the main grid line, which will cause some or all of the cells to fail. For the above reasons, the most significant influence on the function of the cell sheet is the crack that is parallel to the main grid (class 4). According to the results of the study, 50% of the slices came from the crack parallel to the main grid lines.
The efficiency loss of the 45 ° tilt crack is 1/4 of the loss of the main grid line. Cracks perpendicular to the main grid (Class 5) do not affect the fine-grained lines with little impact, resulting in a cell failure area of almost zero. Compared to the crystalline silicon cell surface of the gate line, the overall surface of the thin film lifepo4 battery pack cover a layer of transparent conductive film, so this is a thin film components without cracking one of the reasons. The results show that a single cell in the component failure area of 8% or less, the power of the component has little effect, components of the oblique stripes on the components of power stability has no effect. Therefore, when the cell in the module appears cracked, may produce efficiency loss, but do not talk about hidden crack discoloration.
The core of the cell is the PN junction of the semiconductor, which is in a state of dynamic equilibrium with no other excitation (such as light, voltage, temperature). The number of electrons and holes is relatively stable. If the voltage is applied, the internal electric field in the semiconductor will be weakened and the electrons in the N region will be pushed to the P region and recombined with the hole in the P region (also known as the hole in the P region is pushed to the N region, Region of the electronic composite), after the compound in the form of light auxiliary shot out, that electroluminescence.
When the positive bias is applied, the crystalline solar power batteries will emit light, wavelength 1100nm or so, belonging to the infrared band, the naked eye can not be observed. Therefore, in the EL test, the need to use the CCD camera to assist in capturing these photons, and then processed by the computer to display the form of the image. The higher the number of electrons and holes recombined, the more photons emitted, and the more bright EL images measured; if there are regions of the EL image, Dark, indicating that the number of electrons and holes produced less, on behalf of the existence of defect composite center; if some areas are completely dark, on behalf of the place where there is no electron and hole recombination, or is the light is Other obstacles block the signal can not be detected.
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