We investigate the light-induced degradation of a-Si:H/mu c-Si:H tandem solar cells by applying the Power-Matching-Method (PMM). The PMM allows for a characterization of a cell under various matching conditions by systematically varying the spectral distribution of the illumination. The top cell's thickness was varied from 100 nm to 500 nm for cells with and without SiOx intermediate reflector layer (IRL). The method provides a powerful means of comparing the degradation of differently matched tandem cells. We conclude that the IRL does not significantly affect the stability of our sub cells. The method reveals that only the top-cell degrades significantly under illumination. In addition, the study shows that the PMM is useful for outdoor performance estimations of tandem solar cells or modules. (C) 2015 Elsevier B.V. All rights reserved.