EL
Electroluminescence (EL) is the result of radiative recombination of electrons and holes while applying forward bias current on a solar cell. The light emission from each point of a solar cell is proportional to the voltage. Like with LBIC, badly performing areas with enhanced recombination appear as dark patterns on the EL image. In contrast to LBIC, the EL image is typically taken at a larger current similar to standard working conditions of the solar cell (a few Amperes). This means that the local series resistance more strongly influences the image. Areas of larger series resistances lead to a gradient in the signal. Finger interruptions and metallization issues lead to darker areas.
In this EL system, we are using a conventional digital camera to capture the image, where the short-pass filter of the camera was removed so that the relevant wavelengths can be detected by the CMOS sensor. The power supply can provide a maximum current of 10 A. The capture area can be a whole solar cell using standard optics. We also use a macro objective leading to a spatial resolution of about 4 碌m.
听
听
Examples of electroluminescence images taken with our system on a multicrystalline silicon solar cell are shown below.
