Lock-In Thermography and Related Topics in Photovoltaic Research

Abstract

In this contribution the basic principles of DLIT (dark lock-in thermography) are introduced and typical application examples are shown. These results are compared with that of other solar cell characterization techniques like electroluminescence (EL) and photoluminescence (PL) imaging, which are also very popular in Germany. It will be shown that these techniques are largely complementary to each other. Luminescence techniques are most sensitive for the detection of local recombination centers in the bulk and of series resistance problems of the cells, whereas DLIT is most effective for investigating all problems being connected with the dark current of the cells. A new DLIT technique is introduced which allows a separate imaging of the so-called diffusion current and the recombination current. These two contributions of the dark current are based on different physical mechanisms (recombination in the bulk and in the depletion region, respectively), and their spatial distributions differ significantly. Such investigations are impossible by applying luminescence-based imaging techniques.