Visualizing the performance loss of solar cells by IR thermography — an evaluation study on CIGS with artificially induced defects

Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one im- portant tool to detect these defects on photovoltaic modules. Qualitative interpretation of IR images has been carried out successfully, but quantitative interpretation has been hampered by the lack of “calibration” defects. The aims of this study are to (i) establish methods to induce well-defined electric defects in thin-film solar cells serving as “calibration” defects and to (ii) assess the accuracy of IR imaging methods by using these artificially induced defects. This approach paves the way for improving quality control methods based on imaging in photovoltaic. We created ohmic defects (“shunts”) by using a focused ion beam and weak diodes (“interface shunts”) by applying a femto-second laser at rather low power on copper indium gallium selenide cells. The defects can be induced precisely and reproducibly, and the severity of the defects on the electrical performance can be well adjusted by focused ion beam/laser parameters. The successive assess- ment of the IR measurement (ILIT-Voc) revealed that this method can predict the losses in Pmpp (maximal power extract- able) with a mean error of below 10%.