Comparison of the recombination velocity at grain boundaries gained by lock-in thermography and light beam induced current measurements

Abstract

The surface recombination velocity at grain boundaries can be evaluated by means of Dark Lock-in Thermography (DLIT) or Light Beam Induced Current measurements (LBIC). In this contribution for a first time we apply both methods to the same grain boundaries and compare the results to each other. In spite of the quite similar models, which are the basis of both evaluations, there are quite strong differences in the required interpretation of both approaches. A detailed discussion presents the main issues in comparing recombination parameters of grain boundaries obtained from the different measurements and exposes that the used model represents the LBIC-based method better, but the DLIT-based evaluation proposes a better estimation of the influence of the GB on the solar cell performance. This is possible since DLIT provides a direct measurement of the dark current density caused by the recombination at the grain boundary, whereas the LBIC-based method is mainly sensitive to the recombination in the bulk. For this reason both methods may give similar results under strict limitations, but in some cases the DLIT method cannot be used to calculate a surface recombination velocity at the GB as it is defined in the underlying model.