Defect identification of solar cells with electroluminescence

Solar cell materials can have defects that are not visible by the naked eye. Defects such as small cracks can with time grow larger and negatively affect the performance of the cell and in worst case the entire module or module string. With electroluminescence defects can be identified early on and their development can be followed throughout.

A mono- (left) and multicrystalline cell (right) during electroluminescence photographed in both the visible and near infrared spectrums where defects become identifiable.

Defects of different kind

Cracks, faulty busbars or soldering, and internal resistances can develop in the solar cells during manufacturing, transport, installation or by weather and wind. These defects are rarely visible with the naked eye and are often only identified when they noticeably limit the entire installation's performance.

Electroluminescence makes it possible to detect otherwise invisible defects

With electroluminescence the normal process of a solar cell is reversed, instead om converting light to electricity one converts electricity to light. This process will generate light in the functional parts of the solar cell, meaning that cracks and other defects will remain dark. The emitted light is in the near infrared spectrum and requires special cameras to be obeserved. Many such cameras are susceptible to a wide light spectrum, meaning that visible light often can interfere with the light emitted from the solar cell. A camera with an InGaAs-sensor operates effectively in the spectrum for most types of solar cells, is less sensitive to interferance from visible light and has a low exposuretime, meaning that you also can film with good results, unlike many other sensor types.

Increased understanding across the whole lifecycle

By continually monitoring solar cell modules with electroluminescence it is easier to identify likely causes and risks of cell damage, this knowledge makes it easier to proactively create opportunities for solar installations to remain productive throughout their lifecycle.