A German study has shown that a commercially available camera can accurately measure the efficiency of solar cells after minor modifications and calibration based on an appropriate physical model. The approach could offer a lower-cost alternative to the specialized industrial cameras typically used in laboratories to evaluate the performance of solar cells and panels, which are among the leading sources of clean energy.
Researchers from the University of Stuttgart and Forschungszentrum Jülich modified a commercial camera to capture electroluminescence images of solar cells. Electroluminescence is a technique used to assess the quality and performance of solar cells. The findings were published Tuesday in The Journal of Applied Physics.
Electroluminescence is the light emitted by a solar cell when an electric current passes through it, as a result of charge carriers recombining within the cell material. Analyzing this light can provide information about the cell’s quality and performance.
The researchers focused on measuring external electroluminescent quantum efficiency, a value directly related to the voltage of a solar cell and an indicator of its performance. In general, higher electroluminescent efficiency is associated with better cell performance. The property is usually measured using expensive specialized industrial cameras that require precise calibration to convert captured light signals into quantitative data.
The study showed, however, that a relatively inexpensive consumer camera can also perform quantitative measurements, provided its physical response is properly characterized and the camera is appropriately calibrated.
The researchers used a camera that was relatively well suited to this type of imaging because it lacked the internal infrared-cut filter found in most commercial cameras. Cameras without this filter are also used for infrared photography and night-sky imaging.
Optical Filter
The team placed a long-pass optical filter in front of the camera lens to reduce visible background light. This enabled the camera to capture the solar cells’ electroluminescence in the infrared range and allowed researchers to analyze the intensity of the recorded light.
The researchers said electroluminescence images contain quantitative information beyond simply showing brighter or darker areas. By combining an appropriate physical model of the camera with proper calibration, it is possible to determine the absolute external electroluminescent quantum efficiency.
According to the study, this data can reveal the local quality of a solar cell or module and identify differences in performance between various areas, rather than merely producing an image that shows bright and dark regions without providing quantitative measurements.
The researchers said the method could make electroluminescence measurements more accessible and affordable. However, using a commercial camera does not mean that any ordinary camera can perform the measurements without preparation. Reliable quantitative results require a camera with suitable characteristics, optical modification, an accurate physical model, and appropriate calibration.
In the next phase, the team plans to use the calibrated camera to measure the electroluminescent quantum efficiency and open-circuit voltages of additional solar cells and modules that have not previously been characterized.
The researchers also believe that the same model could be applied to photoluminescence measurements and potentially to measurements conducted in daylight. This could further expand the use of commercial cameras in the characterization of solar cells and modules.
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