Electroluminescence imaging of PV devices: single-time-effect statistics and removal

The statistics and removal of occurring specific image artefacts (i.e. single-time-effects [STE]) during qualitative analysis of EL imaging is discussed. STE are caused by single nuclear particles such as heavy ions, along with neutrons and protons with energies above 10 MeV. When charged particles cross the sensitive region of the CCD matrix, they cause effects of ionization and lead to spots only visible once after signal readout. Depending on whether STE occur in the EL image with sample excitation or in the background image without, they are visible in the corrected EL image as bright or dark spots. These can be confused conceivably with cell defects. Within this work the intensity offset due to STE as well as their occurrence over time is evaluated for multiple EL images. For the examined setup it is shown that the disruptive influence of STE is visible for measured cell voltages under 0.65 V. For this case a robust STE removal method is proposed using an additional EL image taken in series.